A Study of the Determination of Potash Chiefly Concerned with the

Publication Date: May 1917. Cite this:Ind. Eng. Chem. 1917, 9, 5, 504-513. Note: In lieu of an abstract, this is the article's first page. Click to in...
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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY

and t h e cupric hydroxide is transferred t o a IOO cc. Erlenmeyer flask, and by means of a stirring rod t h e paper in the flask is unfolded so t h a t t h e residue is on top, and so t h a t it can be rubbed with a rod. Five cc. of 0.1 N HC1 are then p u t into t h e graduated flask in which t h e complexes were originally made, so t h a t t h e residue clinging t o t h e sides of the flask is dissolved. This solution is then added t o the filter paper in t h e flask and boiled gently. Another portion ( 5 cc.) of 0.1 N HC1 is used in exactly t h e same way. Finally t h e graduated flask is washed with 6 t o I O cc. of water a n d this added t o t h e complexes in t h e Erlenmeyer flask. After t h e residue is dissolved t h e volume of t h e solution in t h e flask is made up t o about 2 0 cc. and 2 g. of powdered potassium bicarbonate are then added as follows: a little (0.2-0.3 g.) of the bicarbonate is first added with a spatula and t h e solution shaken. This precipitates t h e insoluble complexes and t h e excess of cupric hydroxide or carbonate again. After standing one t o two minutes t h e remainder of the bicarbonate is added. On shaking two t o three minutes t h e excess of cupric hydroxide or carbonate is completely dissolved and insoluble complexes are then filtered through paper (S. & S. No. 590, 7 cm. in diameter) and washed with a little water. On returning t h e filter paper t o t h e Erlenmeyer (also washed), adding I O cc. I O per cent acetic acid’ and heating until t h e copper of t h e complexes is dissolved, t h e solution can be titrated iodometrically. As a table of precipitabilities in t h e original paper shows, a correction for solubility in KHCOa is necessary. This technic gives good results with most of t h e insoluble complexes, b u t with leucine t h e technic described in a former paper2 is preferable; this technic required t h e washing of t h e first residue with small amounts of I O per cent KHCOs until t h e filtrates gave no appreciable tests for copper: then t h e insoluble complexes were dissolved in I O per cent acetic acid a n d titrated. It may be possible, by using a n amino acid like glycine which gives a soluble complex, t o replace this bicarbonate solution a n d reduce t h e solubility corrections appreciably. As may be seen from t h e table, I t o 2 mg. of lgucine and CYStine may be determined as soluble complexes. SUMMARY

T h e following improvements in t h e copper method for estimating amino acids are described: I-A simple method for dehydrating and weighing cupric sulfate suitable for making standard copper solutions. 11-A stock suspension of cupric hydroxide, which is very sensitive in its reaction with amino acids, and keeps for months. 111-A method for making and keeping saturated solutions of potassium iodide, containing starch and acetic acid. DIVISION OF LABORATORIES A N D RESEARCH NEWY O R K STATE D E P A R T M ~ OF N THEALTH ALBANY 1 The cystine complex dissolves only slowly in acetic acid. matters a few cc. of N/10 HCl may be added. 1 J. Biol. Chem., 18 (1912). 4.

To expedite

Vol. 9 , No. 5

A STUDY OF THE DETERMINATION OF POTASH CHIEFLY CONCERNED WITH THE LINDOGLADDING METHOD By P. I,. HIBBARD Received December 1, 1916

This study was undertaken for t h e purpose of obtaining a more thorough and exact knowledge of t h e principles involved in t h e determination of potash according t o the Lindol-Gladding2 Method as practiced by t h e Association of Official Agricultural Chemists*29’a0* Although no part of t h e original plan for the study of potash determination, some work was done on the Perchlorate Method a n d is here reported for t h e sake of completeness. As opportunity offered, t h e work has from time t o time extended over many months. The writer feels t h a t results obtained are of sufficient value t o warrant this presentation. T H E LINDO-GLADDIKG

METHOD I N B R I E F

Ten grams of t h e material are boiled in a 500 cc. flask with 300 cc. water for 30 min. T o t h e hot solution ammonia and ammonium oxalate are added in excess t o remove Fe, Ca, Pod, etc. The solution is cooled, volume made t o 500 cc., filtered, a n d a n aliquot of 50 cc. evaporated in a platinum dish. During evaporation, excess of H & 0 4 is added, then t h e residue is slowly heated, finally t o full red, so t h a t t h e residue is white. The salts are dissolved in water, a little HC1 added, and a n excess of HzPtCl8 solution; t h e mixture is evaporated t o paste. The residue is washed free of soluble platinum with 80 per cent alcohol, then sodium a n d magnesium salts, etc., are removed by washing with 2 0 per cent NH4Cl solution and this is removed by t h e 80 per cent alcohol. The precipit a t e is dried and weighed as KzPtCla. MAKING SOLUTION O F MATERIAL TO B E T E S T E D

The volume of water used in making solution is not important with many substances, provided it remains within 50 per cent of t h e official requirement. Ten grams of a n ordinary fertilizer boiled with I 50, 300 and 450 cc. gave 4.78 t o 4.83 per cent K2O as a n average of four determinations on each solution, t h e variation on each being as great as those between t h e different solutions. When t h e substance contains much soluble phosphoric acid or other material which gives a heavy precipitate with ammonia, t h e greater t h e dilution t h e more accurate the result in general, because of t h e occlusion of potash by gelatinous precipitates. If t h e volume in which precipitation takes place is larger there is a smaller proportion of t h e potash in t h e precipitate. By making t h e dilution I in 1000 instead of t h e usual I O in 500, correct results were obtained as shown under “Soluble Phosphates” below. Vigor of boiling causes no perceptible variation in result. Portions heated on a Steam bath, boiled gently over a low flame, or boiled vigorously, gave results within t h e usual limits of error. Time of boiling: Five, ten, thirty or sixty min. boiling gave nearly identical results.

*

Numbers refer t o corresponding numbers in “Bibliography.” PP. 496 and 7.

T H E JO U R N A L 0 F I N D U S T RI A L A iV D E Y G I E E R I S G CH E M I S T R Y

May, 1917

A m m o i t i a u s e d t o m a k e the s o l u t i o n a l k a l i n e a f t e r One, five a n d twenty-five cc. gave results boiling: within t h e usual limits of error; sufficient to make alkaline is enough. I n order t o remove P20Sas much as possible, ammonia i n i t s t b e a d d e d b e f o r e ammoizium o x a l a t e . If t h e oxalate is added first i t removes t h e calcium, which is needed t o form a n insoluble precipitate with t h e P 2 0 5 ,thus leaving t h e latter in t h e filtrate as ammonium phosphate, which is, during ignition, converted into insoluble metaphosphate tending t o cause errors which may be large.3 T h e quantity o f a n t m o i t i u m o x a l a t e u s e d should be t h e least t h a t will suffice. I n many cases excess will do no harm, b u t when soluble P2O5 is present, any oxalate over t h e amount necessary t o combine with t h e calcium tends t o make more P205 go into t h e solution as ammonium phosphate, CaXH4P04 (XH~)Z(COO)~ = Ca(C00)* (NH4)2HP01 NH8 A mixture of acid phosphate and kainit treated b y t h e Official Method, b u t varying t h e amounts of ammonium oxalate, gave t h e results shown in Table I. This is not intended t o indicate which result is nearest correct, b u t only to illustrate t h e effect of ammonium oxalate. I n general. t h e higher results seem due t o soluble Pz05. When t h e substance contains much acid phosphate there is no calcium remaining in solution after making alkaline with ammonia, hence i t is not necessary t o a d d ammonium oxalate, which should be avoided as indicated above. VARIOUS IMPURITIES-sodium s a l t s have very little effect in moderate amounts except during t h e final ignition when they cause t h e residue t o be more readily fusible. M a g r c e s i z i i n a n d calcium aid somewhat in burning by keeping t h e residue more porous a n d less likely t o fuse. The chief effect of all these is seen in t h e purification of KzPtC16 ( q . v . ) Calcium is removed by ammonium oxalate without loss of potash. I n case there is considerable organic matter in the solution some calcium and iron may remain after treatment with ammonia a n d ammonium oxalate. S o d i u m a n d n t a g n e s i u m together in moderate amounts have little effect, except in later processes. Irolt is chiefly removed b y ammonia. I n t h e presence of soluble carbohydrates a n d proteids a n d some other forms of organic matter, some iron is held in solution in presence of ammonia and remains t o be separated from t h e K2PtC16. The precipitate with ammonia occludes some potassium. T o secure accurate results i t must be treated like t h e phosphate precipitate.

+

EFFECT

+

+

OF SOLUBLE PHOSPHATES

Materials in which potash is t o be determined frequently contain w a t e r - s o l u b l e fihosfihates. I n t h e Lindo-Gladding N e t h o d these are supposed t o be removed b y ammonia. Ammonium oxalate is t h e n added t o remove calcium. I n such cases P205is usually present in t h e filtrate in proportion t o t h e amount of ammonium oxalate used. This fact was

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published by De Roode7 in 1895. But if calcium or barium is added in excess before ammonia, no P 2 0 5 is found in t h e filtrate. Sufficient CaO alone completely precipitates P205during boiling, without any ammonia. Attempts t o remove P205 completely b y boiling with excess of C a C 0 3 or B a C 0 3 failed. Excess of CaClz or x'IgC12 added before the ammonia completely remove P?05;CaC12 is preferable, as it is easily removed b y ammonium oxalate. But since excess of oxalate causes P 2 0 5t o go into solution as ammonium phosphate, t h e phosphate precipitate must be removed before adding ammonium oxalate t o precipitate calcium. Ten grams of a mixture of equal parts of acid phosphate and kainit y e r e treated as usual for a potash determination and varying amounts of ammonium oxalate added. I n the filtrates P20j and K 2 0 were determined with t h e following results: TABLE I-EFFECT OF

.431MONICM O X A L A T E

Grams Oxalate A d d e d . . .. . . . . . . . . . . . 0.0 0.5 2.0 Grams PzOh Found... . . . . . . . . . . . . . . . 0.0004 0.0032 0.0117 Per cent K20 Found . 4.54 4 53 4.62

5.0 0.0228 4.iO

The higher results for K 2 0 are partly due t o P 2 0 5 not removed from t h e KzPtCls, as will be shown later; hence i t should be removed before adding ammonium oxalate. But as t h e presence of P205in t h e filtrate after adding ammonium oxalate is due t o insufficient calcium t o form Ca3P208i t seems unnecessary t o add ammonium oxalate t o remove calcium which has already been completely removed b y excess of Pz05 when made alkaline with ammonia. Hence in proceeding by t h e Lindo-Gladding Method, if t h e material contains much acid phosphate, omit adding ammonium oxalate. Even t h e n t h e filtrate will usually contain some P20j, t o prevent which excess of calcium is added before adding ammonia. This increases t h e volume of t h e precipitate. Occlusion of potassium by this heavy gelatinous precipitate18 is19 t h e largest source of error, chemically, in t h e Lindo-Gladding Method. I t may amount t o from I t o I O per cent of t h e amount of potassium present. h mixture of I O g. acid phosphate and I g. K?S04gave 5.40 per cent K20 by t h e regular method instead of j . 7 2 per cent! t h e amount actually present, a deficiency of nearly 6 per cent. The error due t o occlusion is partly offset by t h e opposite error of diminished volume on account of t h e bulky precipitate. These errors are commonly known, a n d published, b u t no one seems t o h a r e devised a satisfactory plan for overcoming them. The alternate official modification of t h e Lindo-Gladding Method, which consists in washing t h e material on a filter t o extract t h e potash, instead of boiling it with water, is helpful, b u t only partly overcomes the difficulty. The higher results obtained by this method may be attributed t o t h e smaller volume of t h e precipitate and t o t h e increased dilution. I n order t o overcome t h e loss due t o occlusion, t h e only feasible methods seem t o be re-solution and reprecipitation, .or greatly increased d i l ~ t i o n . ' ~ RE-PRECIPITATIOX

METHOD

Boil I O g. of t h e material with zoo cc. of water, adding I t o z g. CaC12 t o supply enough Ca t o form

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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

CaSPzOa with all the P z O present. ~ After boiling a few minutes, make alkaline with ammonia and filter a t once. A 9 cm. filter in a Io-cm. Buchner funnel with suction is most convenient. Suck as nearly dry as possible, wash a little, then wash t h e precipitate off t h e filter, back into t h e beaker, t o a volume of I O O t o 1 5 0 CC., add a little HC1 t o dissolve t h e gelatinous precipitate, but not enough t o act on t h e insoluble matter. Heat t o boiling and again make alkaline with ammonia. If enough CaClz was added in t h e first precipitation no more is needed here. Filter as a t first. I n most cases this is enough, but t o sqcure all t h e potash one or two more re-precipitations will be necessary. The filtrates are combined, if desirable, concentrated t o about 400 cc., in a 500 cc. flask, and while hot, sufficient ( I t o 3 g.) ammonium oxalate is added t o precipitate all t h e calcium in solution. Some excess of ammonium oxalate here does no harm. Cool, make up t o 500 cc., filter and t a k e a 50 cc. aliquot for t h e potash determination as usual. T h e precipitate of calcium oxalate seems t o cause very little error. LARGE DILUTION METHOD

Place 1.111 g. material in a liter flask, add 800 t o goo cc. of water a n d sufficient CaClz t o combine with t h e PlOa, boil 30 minutes, make alkaline with ammonia, cool, make volume t o 1000 cc. and filter. T o t h e filtaate a d d dry ammonium oxalate t o precipitate all calcium. Shake a few times for a n hour or so t o complete the precipitation of t h e calcium. Filter on a dry filter. Take 900 cc. of t h e filtrate ( = I g. substance) and proceed with t h e potash determination. This method is less time-consuming for t h e actual manipulations, b u t requires much longer for t h e evaporation a n d affords no opportunity for a duplicate determination on the same solution. I n most instances i t is likely t h e re-precipitation method will be found preferable. I n case t h e solution is difficult t o filter, t h e dilution method may be preferable. R ~ S U MA S~ T O SOLUBLE PHOSPHATES

I n potash determination, soluble PZOSis t h e cause of three errors: (I) Occlusion of potash b y the heavy precipitate, tending t o low results; ( 2 ) volume decreased b y the precipitate, tending t o high results; (3) f o r m a t i o n of a n insoluble substance in the later part of the determilzation, causing high results. Besides these t h e soluble phosphate has a bad effect on t h e platinum dishes during ignition. These errors may or may not balance exactly so as t o give a correct result. If accuracy is desired, some method, such as above outlined, must replace t h e usual unmodified Lindo-Gladding method. Soluble proteids a n d carbohydrafes frequently occur in materials in which potassium is t o be determined. Hence their effects were studied. Soluble proteids make t h e solution more difficult t o filter and t h e residue more difficult t o burn, b u t the result is not much affected. When a few milligrams of gelatin were added t o pure KC1, t h e result obtained for Potash was t h e same as for pure KCl. M a n y organic substances tend t o prevent complete precipitation of iron a n d calcium b y ammonia and

Vol. 9 , No. 5

ammonium oxalate. When such are present, more or less iron and calcium will be found in the mixture of salts after the ignition. An infusion of alfalfa h a y was mixed with iron a n d calcium solutions and treated with ammonia and ammonium oxalate. The filtrate still contained some iron a n d calcium. Infusions of ordinary tankage and b a t guano fertilizer act in t h e same way. Extracts of bone meal, tankage, garbage tankage and bat guano were made a n d potash determined in them. Then t o t h e same amount of t h e solutions was added a known amount of KC1 and potash determined. The results tended t o be low, but with proper care in burning were very good. Soluble silica is often present in potash solutions. During t h e ignition i t becomes insoluble and later must be filtered out before evaporating t h e solution with platinum. If carefully done this causes no loss. However it has been found better t o a d d a few drops of hydrofluoric acid t o t h e potash solution during evaporation. This entirely removes silica a n d is itself removed during t h e ignition so t h a t it is not necessary t o filter after taking up the salts in water. Presence of hydrofluoric acid in t h e solution in which KtPtCle is formed is not permissible, as it causes very erratic results. If desired t o remove silica b y hydrofluoric acid after t h e ignition it is necessary t o replace hydrofluoric acid by several evaporations with hydrochloric acid before evaporating t h e solution with platinum. S t a n d i n g before j l t r a t i o n : It has been said by someone that in some cases, particularly in presence of soluble phosphates, more nearly correct results were obtained if t h e solution after boiling a n d addition of ammonia and ammonium oxalate is made up t o volume a n d let stand several hours before filtration. The presumption is t h a t diffusion of t h e potash occluded in t h e heavy precipitate occurs, thereby increasing t h e amount of potassium in solution. Several portions of a fertilizer containing considerable acid phosphate were treated by t h e Official Method a n d t h e solutions allowed t o stand for periods of one-half hour, 18 hours and 7 days before filtering. Variations were too small t o be conclusive, b u t tended t o show lower results for t h e longer standing before filtration. The alternate Official Method of washing the potash out of the material placed on a filter instead of extracting by boiling has been found preferable in many cases, if not all. The advantages of this method seem t o be due chiefly t o t h e less amount of foreign matter introduced into t h e solution. I n t h e boiling method there is considerable humus matter brought into solution after addition of ammonia. This is avoided in t h e washing method. I n t h e presence of acid phosphate t h e advantage of this method is probably due t o the larger volume in which precipitation takes place. The referees of t h e Association of Official Agricultural Chemists have found t h a t t h e washing method tends t o give higher a n d more nearly correct results. I n connection with my study the figures given in Table I1 were obtained.

May, I 9 1 7

T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y

TABLEII-COMPAR~SON OF BOILINGAND WASHING METHODS PER CENT KIO IN SOLUTION MADE B Y No. Boiling Washing CHARACTER OF SAMPLE 7 . 4 6 7.52 4960 Tankage and KzSO4.. . . . . . . . . . . . . . . . 2.62 2.56 Bat Guano.. ....................... 5359 1.34 1.36 Garbage Tankage.. . . . . . . . . . . . . . . . . . 5988 4.78 4.91 Mixed Complete Fertilizer. . . . . . . . . . . 5361 5.50 5119 Tankage and KzS01.. . . . . . . . . . . . . . . . 5771 4.78 'Tankage and KzSO4. . . . . . . . . . . . . . . . . 5666 4.83 5.34 Mixture containing Acid Phosphate.. 5.37 5544 4.90 4.68 Mixture of Acid Phosphate and Kainit.

. ..

The washing method is perhaps more laborious t h a n t h e boiling method in making t h e solution, b u t this is offset by greater ease of t h e subsequent operations. T h e Official Method prescribes t h a t 2 . 5 g. of t h e material placed on a 12.5 cm. filter shall be washed with successive small portions of boiling water till t h e filtrate amounts t o about 2 0 0 cc.; 2 cc. concentrated HC1 are added a n d the mixture is heated t o boiling; ammonia a n d ammonium oxalate are then added, after which t h e procedure is as usual, using a n aliquot of 50 ,cc. ( = 0 . 5 g. original substance). I n many cases i t is desirable t o use a n aliquot representing I g. of t h e substance. If t h e above instructions are followed this requires t h a t I O O cc. be evaporated, which is not so convenient as a 50-cc. aliquot. If a more efficient method of washing is used t h e double dilution may be avoided. An ordinary carbon filter t u b e of 30 mm. diameter fitted with a plug of absorbent cotton is very satisfactory. Using this with suction, I O g. of material may be completely extracted by zoo cc. of boiling water. Repeated tests have shown t h a t potash remaining after this amount of mashing is insignificant, i. e . , less t h a n I mg. Filter paper on a filter cone, used with suction, gave 5 mg. potash in t h e third IOO cc. of washing. Filter paper without suction is still less efficient. Ten grams of a material containing about 5 per cent potash were washed with I O cc. portions of boiling water on a 1 1 cm. filter. I n each successive IOO cc. of extract, potash was determined. I n t h e first I O O cc. were found 4.88 per cent; in t h e second, 0.16 per cent; in t h e third, 0.05 per cent; in t h e fourth, 0.04 per cent; in t h e fifth, 0.01 per cent. A folded or fluted filter is still less efficient t h a n t h e smooth filter, b u t is more rapid. Because t h e whole volume of water used with t h e filter tube passes through t h e substance, instead of partly through t h e sides as with a n ordinary filter, t h e tube is much t o be preferred for this extraction. FILTRATION OF THE POTASH SOLUTION

After the solution has been prepared and made up t o proper volume it must be filtered t o separate t h e insoluble matter. Three variable factors concerned in this operation may have some effect on t h e result: ( I ) evaporation, ( 2 ) turbidity of filtrate, (3) adsorption by the filter. The time factor is most important. If the solution filters very slowly there may be a n appreciable concentration unless evaporation is prevented. Two ordinary fertilizer solutions prepared for potash determination were filtered through 18.5 em. folded filters, and t h e loss by evaporation was found t o be ' / z t o I cc. per hour. This is unimportant in most cases, b u t if filtration is prolonged for several hours,

SO7

evaporation should be avoided by t h e use of a suitable cover. It has been found expedient t o use a linen filter for those solutions which filter very slowly. If t h e filtrate is returned t o t h e filter for a few minutes a t first, till a film is formed on the surface of the cloth, i t will come through fairly clean and much more rapidly t h a n through a paper filter. The clarity of thefiltrate seems t o make little difference in t h e final result unless t h e liquid contains insoluble matter not removed by ignition. I n direct experiments variations of t h e results due t o cloudy or clear filtrates from t h e same solution were within t h e limits of ordinary experimental error. Selective adsorption of potash by the filter paper from t h e solution passing through it was too s m l l t o be detected with certainty by t h e usual analytical methods, though there was some indication of such action. It may be assumed t h a t if a t least IOO cc. of the solution are filtered before a n aliquot is taken out, any loss due t o adsorption by t h e filter is negligible. EVAPORATION OF THE SOLUTION

The Official Method directs t h a t 5 0 cc. of the solution be placed in a platinum dish and evaporated nearly t o dryness, when I cc. of I : I HzS04 is added, and evaporation continued t o dryness. Ordinarily this is t h e best procedure. But sometimes it is more convenient t o add t h e acid a t once, thus preventing escape of ammonia which might be undesirable. Numerous experiments in connection with this study show t h a t there is no perceptible difference in t h e result due t o time of adding t h e acid, whether first or last. All t h a t is necessary is t h a t t h e solution be acidified before becoming dry, in order t o prevent loss of KC1 on ignition. To prevent loss it is important*chat water be driven off as much as possible before beginning t h e ignition. It is frequently desirable, especially when t h e solution contains salts having water of crystallization or which are liable t o decrepitate, t o heat t h e dish with residue in a n oven somewhat above the boiling point of water, till quite dry, before beginning t h e ignition, thus avoiding loss by spattering. IGNITION OF THE RESIDUE

It seems probable t h a t in ordinary practice faulty ignition is responsible for more inaccurate results in potash determinations t h a n any other single cause. Too rapid heating causes loss of material by spattering, and causes great difficulty in removing the last of t h e carbon, due t o fusion of t h e salts on the surface whereby the interior is protected from oxidation so t h a t t h e .carbon does not burn. If in this condition heat is further increased t h e whole mass fuses and t h e sulfates are reduced t o sulfides by t h e hot carbon. This is injurious t o t h e platinum dish as well as t o correctness of t h e determination. A great deal of work was done in the effort t o find a method which would expedite t h e ignition as well as prevent loss. (I) The essence of the whole matter consists in proper regulation of t h e temperature, and this is not t h e same for all cases. Heating must be so gradual t h a t t h e H z S O r is slowly volatilized without spattering.

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T H E J O U R N A L O F I N D U S T R I A L A N D E'VGIiVEERING C H E M I S T R Y

After t h e mass is dry i t should never be heated red hot till a f t e r t h e c a r b o n has been all b u r n e d oJ. After this i t may be heated t o fusion of t h e salts, momentarily. LOSSof potash occurs if t h e salts are kept near fusion for any length of time. I t is commonly believed t h a t K2S04 is not lost in this way. But i t is found t h a t a t about t h e fusion temperature, there is gradual loss of SOS, so t h a t K20 is formed a n d volatilized. However, there is absolutely no need for such loss as i t is unnecessary t o heat above redness, a t which temperature K H S 0 4 is changed t o K2S04. Even if a little of t h e acid salt remains i t will do no harm. A good muffle is t h e most convenient device for making these ignitions in t h e most satisfactory manner. After removing t h e dish a n d residue from t h e steam b a t h i t is placed in t h e cold muffle, which should be heated so slowly t h a t there is no spattering and t h e temperature raised t o very low red in about a n hour, b y which time t h e carbon should be all burned off without fusion of t h e salts. If a muffle is not available t h e dish may be heated a t first on a hot plate till t h e liquid is evaporated, then placed on a triangle 8 cm. above t h e flame of a n evaporating burner. The flame should be as low as possible a t first, a n d gradually increased t o burn off t h e carbon below red heat. A piece of sheet metal, platinum, aluminum or iron held as a cover about I cm. above t h e dish simulates t h e action of a muffle a n d hastens t h e burning. ( 2 ) Prevention of spattering when beginning t h e ignition is difficult if t h e solution contains no organic matter. The presence of I O mg. of sugar helps materially t o avoid spattering a t this stage. On heating with t h e sulfuric acid t h e sugar puffs u p into a porous mass in its well known manner, a n d encloses t h e salts so t h a t they are less likely t o be projected from t h e dish if t h e heating happens t o be too rapid. When t h e mass becomes dry t h e carbon burns off easily without causing loss of potassium. For this purpose I O mg. of sugar is a suitable amount. During this investigation sugar has been much used in this manner, greatly assisting t o avoid loss. I t is useful only when t h e solution contains very little other organic matter. As free H2S04 a n d ammonium salts are t h e chief agents in causing this trouble, they should be kept as low as possible. Free H2SO4and ammonium oxalate cause considerable effervescence: if, instead of H2S04,a n equivalent amount of ("4)2S04 is used, t h e residue becomes dry on t h e steam b a t h , so there is no effervescence on heating, b u t there is likely t o be decrepitation. which may be avoided b y first heating in an oven a t 110' C. I n general there seems t o be little gain from t h e use of ( S H 4 ) 2 S 0 4in place of &Sod. Several other substances were tried t o prevent spattering. Ammonium salicylate seemed most efficacious, b u t finally i t was decided t h a t t h e official treatment with H2S04 was best, with addition of a little sugar when t h e solution contained b u t little organic matter. Much effort was made t o find a means of hastening t h e burning off of t h e residue from solutions containing proteids a n d sodium salts such as those prepared from tankages or b a t guanos which are very slow

V O ~9. , NO.5

burning. Ammonium nitrate helps, b u t i t must not be added till after free HzS04 is gone, as in t h e last p a r t of t h e evaporation there is loss due t o lively effervescence, so t h a t it affords little gain in time. Magnesium nitrate has a similar effect. Magnesium acetate may be added t o t h e liquid before i t is evaporated. During ignition hlgO is formed; this tends t o prevent fusion and gives a greater surface so t h a t combustion is more rapid. But if enough magnesium is used t o help much i t is troublesome in subsequent operations. Soluble phosphates cause difficulty in burning. CaC12, or MgC12, sufficient t o form t h e corresponding phosphates helps some, b u t it is best t o remove t h e phosphates during t h e preparation of t h e solution. Sometimes, when very difficult t o burn white, i t is better t o take up t h e residue with water a n d dilute hydrochloric acid and remove t h e carbon b y filtration. If t h e unburnt matter is small i t may be neglected, if large it should be again ignited a n d extracted, t h e soluble part being added t o t h e main solution. If t h e solution contains soluble silica i t is removed in t h e same manner, without difficulty, b u t as above mentioned, b u t it is more neatly removed b y adding hydrofluoric acid to t h e solution before evaporation. REMOVAL OF AMMONIUM SALTS AXD ORGAKIC MATTER

BY EVAPORATION

WITH AQCA REGIA

Removal of ammonium salts in this way was long ago published in Crooke's "Select Methods," a n d has been advocated by ~ ~ 0 0 r efor 9 t h e preparation of potash solutions for analysis. Instead of placing t h e solution in a platinum dish t o be evaporated, it is placed in a zoo cc. Jena Erlenmeyer flask, 2 cc. " 0 3 and I cc. HC1 added. The solution is boiled, finally t o dryness on a hot plate; t h e ammonium salts are thus decomposed and volatilized. If t h e solution contained much organic matter or oxalic acid, more or less of t h e m will remain. If the amount of these substances is small, t h e y are completely removed by two evaporations with aqua regia, in this manner. The final temperature should reach 160' C. in order t o volatilize oxalic acid. After this t h e residue may be freed of nitric acid. b y again evaporating with a little HC1. The residue is now quite suitable for the determination of potash. This method is slower, b u t takes less care t h a n t h e ignition method, and in some cases may be preferable, as no platinum dish is required. SOLUTION OF RESIDUE AFTER IGNITION

The ignited residue is dissolved in water, with addition of a few drops of HC1. I t is best t o a d d only a few cc. of water a t first, together with 0.5 cc. of HC1, placing t h e dish on t h e water b a t h and heating a few minutes t o see if there is any insoluble matter. If but little water is used t h e acid works better t o dissolve portions of t h e residue which are insoluble in water alone, such as iron oxide a n d CaSOj. After a few minutes heating, a n y insoluble residue should be filtered out. Several cc. of HC1 may be used, if advantageous. On evaporation of t h e solution t h e acid is removed without harmful effect. If t h e solution contained silica i t is removed b y filtration without influence on t h e result, although it is more simply

&fay, 1917

T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY

removed by t h e use of hydrofluoric acid during t h e first evaporation as already explained. I t is not permissible t o use hydrofluoric acid after t h e ignition, as it is not completely removed by evaporation a n d causes low results, probably b y replacing some of t h e C1 in K2PtC16 by F. Calcium sulfate is somewhat difficultly soluble but should cause little trouble if enough HC1 is used, and later considerable water. Some kinds of organic matter combine with iron so t h a t it is not removed b y ammonia in preparation of t h e solution. I n such cases t h e iron is found as oxide in t h e ignited residue. Strong hydrochloric acid dissolves i t , so t h a t filtration is not usually necessary, b u t t h e iron makes trouble in t h e later operations of purifying K2PtClC. SEPARATIOX OF

K2PtClb

I n order t o obtain pure K2PtC16 i t is necessary t o observe certain condition^.^ The potash solution must be sufficiently dilute so t h a t there is no precipitate formed on adding H2PtCle. If t h e precipitate forms at once it is impure and t h e crystals are too small t o be filtered and washed easily. So long as t h e solution is acid t h e amount of hydrochloric acid present is not important. Free H2S04 should not be present. But if some remains as KHSO, or NaHSOi it does no harm. When there is much sodium present t h e amount of platinum used should not be much more t h a n enough t o combine with all t h e potash, because it is much easier t o remove sodium as S a C l or Na2S04 b y means of NH,Cl wash t h a n t o remove i t from t h e precipitate as Ka,PtCls by washing with 80 per cent alcohol. When much Na2PtC15 is formed t h e result is very likely t o be too high, due to its imperfect removal by alcohol. I n this case it is better t o begin t h e determination over again with a new aliquot of t h e original solution. If this is not convenient t h e impure precipitate may be purified as follows: Dissolve in hot water, a d d a few drops of f o r m x acid and evaporate t o dryness. T a k e u p in water, filter out t h e reduced platinum a n d proceed with t h e filtrate as a t first, adding less platinum this time. I n absence of much sodium t h e amount of platinum used is not important, provided there is enough t o combine with all t h e potash. Nitric acid or nitrates must be absent. Organic matter reduces platinum hence must not be present. The solution should be evaporated with PtC14 till t h e residue is pasty, not dry. I n most cases this is not important, but when iron is present it is quite essential. When t h e solution containing FeC13 is evaporated t o dryness, some of t h e iron becomes, by loss of chlorine. insoluble in t h e NHICl wash and hence remains with t h e precipitate, causing high results. PURIFICATIOK OF K2PtC16 The K2PtC16 is purified by washing with So per cent alcohol a n d then with 2 0 per cent NH4C1, which is removed by again washing with 80 per cent alcohol. A correct result depends very much on t h e proper conduct of these purifications. If a Gooch crucible or other efficient filter is used j or 6 successive IO-cc.

509

portions of each wash will generally be adequate. The precipitate of K2PtC16 is much more soluble in 80 per cent alcohol t h a n in t h e NH4C1 wash, hence i t is better t o depend on removal of most of t h e impurities with t h e latter t h a n t o t r y t o remove them as double platinum salts by using a n excess of platinum a n d washing them out with 80 per cent alcohol.17 A small amount of hydrochloric acid 9 ? 1 5 added t o these washes sometimes increases their effectiveness in removing impurities, b u t a t t h e same time it increases their solvent action on K2PtC16. A quantity of 0.33 g. K2PtCla washed with various solutions on a Gooch crucible lost about as follows: TABLE111-LOSS O F KiPtCls B Y 6 CONSECUTIVE WASHINGS O F 10 CC. EACH PERCENTSTRENGTH Gram KQPtClaLost Alcohol Solution 9 9 . . ............................ 0.0002 . . . . . . . . . . . 0.0004 Alcohol Solution 8 5 . . . . . . . . . . . . . . . . . . . . . . 0.0010 Alcohol Solution Alcohol Solution NH&l Solution NHaCl Solution

60..............................

...........

0.0025 0.0020

per cent HC1.. . . . . . . . . . . .

0.0003

80 (denatured)

20 20

4- 5

............

T o show how much washing is required t o purify K2PtC15, several portions of a solution of KC1 were evaporated with platinum as usual, and t h e precipitates filtered off on Gooches. Each of t h e several filter crucibles received a different amount of washing; those showing highest weights had least washing. I n each case there was taken KC1 equal t o 0.3304 K?PtC16 with o . o j g. NaC1, a n d a slight excess of platinum. The precipitate was given t h e specified number of washings with alcohol; then the washing was completed with KH4C1and again with alcohol as usual. The weight of the precipitate \Then washed with one portion of I O cc. of 9 j per cent alcohol was 0.3383, with z washings 0.33 j z , 3 washings 0.3337, 4 washings 0.3301; this shows t h a t all t h e soluble platinum had been removed before adding ”IC1 by four IO-cc. washings with alcohol. T o show how many times t h e precipitate must be washed with alcohol t o remove t h e NH4Cl wash a similar experiment was performed. The weight of t h e precipitate after one wash with alcohol was 0.3330, after 2 washings 0.3314) 3 1%-ashings0.3306; thus three washings of I O cc. each of alcohol were sufficient t o remove all t h e NHrC1 wash. When t h e precipitate of K2PtCls is mixed with various impurities such as C a S 0 4 , Na2S04and icfgSO4, a little more time a n d stirring in t h e dish are needed to remove t h e foreign material. hlost impurities dissolve in t h e NHJCl wash in a few seconds, but CaSOl is much slower. Calcium sulfate, 0.06 g . , is soluble in I O cc. NH4C1in a few minutes. Na2S04is easily soluble in NHIC1 and quickly removed so long as it remains as such. B u t if a n excess of platinum has been used so t h a t there is considerable Na2PtC16 formed, t h e results are very likely t o be high. This salt is b u t slowly soluble in alcohol, so t h a t it is quite likely t o remain after completion of t h e first washing with alcohol. When NHIC1 is added, ammonium and sodium exis formed change acids so t h a t insoluble (“4)2PtC16 a n d causes high results. A large amount of Na2S04 mixed with a little potash usually causes low results

T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y due t o much washing necessary t o remove i t , or t h e result may be high from lack of washing. Sodium chloride is much more easily soluble in NH4Cl t h a n is Na2S04. A 20 per cent solution of NaCl dissolves KzPt Cle easily. Therefore if t h e determination contains much NaC1, this dissolves in t h e water of t h e PU"4C1 forming a solution of NaCl which dissolves t h e KzPtCl6;leading t o low results. But if the sodium is present as Na2S04, this action does not take place so much; hence it is best t o convert sodium t o sulfate before attempting t o separate i t from potassium. Potassium chloride (0.19.) 5 g. NaCl treated with platinum a n d precipitate washed with 80 per cent alcohol and 20 per cent NH4C1 gave 0.3173 and 0.3152 g. KzPtCls instead of 0.3285 g. required by theory. When t h e NaCl was replaced by 5 g. Na2S04t h e result was 0.3200 and 0.3130 g., when evaporated rapidly in t h e usual; manner. I n this way t h e crystals of KtPtCle are very small and hence were dissolved by the washing. B u t when t h e evaporation was so slow as t o require 24 hrs. t h e crystals were much larger and 0.3245 and 0.3226 g. were obtained. A still slower evaporation gave 0.3300 g. KzPtC16. All of these contained traces of sob, though t h e larger crystals formed by slow evaporation were purest. More correct results in separating a small amount of potassium from much sodium are obtained, by first precipitating t h e potassium as cobaltinitrite; this is dissolved in hot dilute HCl (I : I) a n d t h e potassium separated from t h e solution by platinum in t h e usual way. I n this way t h e sodium remains in t h e watery solution with t h e excess of cobaltinitrite reagent, as it is not necessary t o evaporate t h e solution t o separate all t h e potash. T h e cobalt is easily removed from t h e KtPtCl6, partly by t h e alcohol wash, partly by t h e NH4Cl 5 g. Na2S04separated by wash. Thus 0.1 g. KC1 t h e cobaltinitrite method, as above outlined, gave 0.3304 a n d 0.3282 gram KzPtCle; KC1 alone gives 0.3285 g. It seems probable t h a t t h e same method will prove superior t o the platinum method for separating potassium from much magnesium or calcium.26 Because of its solvent actions on KzPtCle,NaCl cannot replace NH4Cl in the wash solution. Potassium chloride acts in t h e same way and is further objectionable because of its low solubility in 80 per cent alcohol. Sodium phosphate in mixture with KzPtCl6 is likely t o cause high results, as i t is imperfectly removed by t h e wash solutions; however, i t is dissolved by t h e acid alcohol before mentioned so t h a t a good result is obtained. Phosphate of course should be removed by t h e primary purification with ammonia and ammonium oxalate. Magnesium (0.01 g.), present as sulfate, caused a lowering of KzPtCle from 0.3285 g. (theory) t o 0.3263 g. (found). T h e precipitate is pasty a n d difficult t o wash free of excess platinum. NHICl removes t h e magnesium salts easily. When present as CaC12, 0.14g. calcium produced hardly any perceptible effect, b u t when t h e amount was 0.70 g., t h e KzPtCle found was 0.3255 g. instead of 0.3285 g.

+

+

taken. EFFECT OF SOLUBLE

PzOs

A small amount of phosphoric acid seems t o have no

Vol. 9, No. 5

appreciable effect in the solution from which potassium is precipitated by platinum. But if t h e phosphoric acid amounts t o I O mg. or more it causes high results for potash. This apparently is due t o formation of substances not readily soluble in a0 per cent alcohol or t h e NH4C1 wash, such as Ca3P2O8. I n some cases both calcium and phosphoric acid may remain in solution after adding ammonia and ammonium oxalate. Acid alcohol removes these substances from t h e KZPtCls and tends t o give a correct result. However, it seems best t o avoid presence of phosphoric acid in t h e solution from which potash is t o be separated b y platinum. If ammonium phosphate is present in t h e potash solution which is evaporated with HzS04 and ignited, t h e phosphoric acid remains as a n insoluble metaphosphate as shown in Bull. 49, p. 44, Division of Chemistry, U. S. D. A.3 This may cause either positive or negative errors and should be avoided by excluding phosphoric acid. 0.1 g. KC1 -I-0 05 g. NazHPO4 gave 0.334 & 0.332 g. KsPtCla (impure) 0.1 g. KCl 0.10 g. iTazHPO4 gave 0.337 & 0.339 g. KiPtCls (impure) Washed with acid alcohol this became 0.330 & 0.331 g. KlPtClr (impure)

+

0.1 g. KCI without NnzXPOd gave 0.33 1 g. RzPtCls

FILTER F O R KzPtCle A variety of filters for washing and collecting t h e precipitate have been tried. Of these t h e ordinary Gooch crucible with a good mat ( a t least in. thick) of well prepared asbestos is most reliable. A glass tube about 16 mm. in diameter, 60 mm. long, t h e t o p widened t o 23 mm., t h e bottom drawn out and narrowed t o a 4 mm. tube 5 0 mm. long, is very convenient. A wad of glass wool is packed into t h e bottom and covered with an asbestos mat. This filter is used with moderate suction. Such filters are most convenient and time-saving and have been in use here more t h a n I O years. They have t h e defect t h a t t h e glass wool gradually breaks up and is lost into t h e filtrate with consequent loss of weight of t h e filter and inaccuracy of results. I n general and for ordinary purposes this defect is negligible. A similar tube fitted with a finely perforated platinum disc for supporting t h e asbestos mat is free of this defect and is even better t h a n a Gooch crucible. Such a filter is described by SchollenbergerzZexcept t h a t he uses a linen disc on top of t h e platinum disc t o hold the asbestos. This filter is quite effective a n d convenient, but is not suitable for weighing t h e precipitate on account of changes in weight of t h e linen disc due t o action of chemicals a n d of heat of drying. He recommends t h a t t h e K2PtCl6be washed out into a platinum dish in which it is dried and weighed. When the filter contains no organic matter, such as cloth, i t is suitable for weighing t h e precipitate without first washing into a dish. A filter tube fitted with a cotton plug supporting a filtering layer of paper pulp is very efficient b u t as above indicated cannot be used for direct weighing of t h e precipitate. Filter paper is much less convenient t h a n any of t h e above mentioned filters; besides, if used for accurate work, t h e filter paper requires a special preparation by washing in order t h a t soluble matter be not carried into t h e solution with hot water when washing out t h e

May, 1917

T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y

511

purified K2PtC16. When very small quantities of removal from t h e oven. After standing about IO min. i t potash are t o be weighed, most of t h e above mentioned is apparently cool, but t h e weight indicated is about filters are not sufficiently accurate. Filter paper I mg. less t h a n after it has stood half an hour. After washed successively with dilute HCl, NaOH, HC1, this t h e weight is practically constant if it is kept in a H 2 0 , and 80 per cent alcohol serves pretty well, b u t desiccator. Standing in open air there is some variacannot be safely used more t h a n once as it gives up tion in weight, usually a gain after 24 hrs. soluble matter t o hot water after heating t o remove P E R C H L O R A T E M E T H O D FOR POTASH'1 alcohol. A felt of well washed paper pulp i n , a Gooch I n any case where the original solution contains so4 crucible is more convenient b u t otherwise no better. I n use, after t h e precipitate is properly purified, either which must be removed in order t o apply the perof these paper filters is dried t o remove t h e alcohol, chlorate method this method is t o t h a t extent more then t h e K2PtCl6is washed out with hot water into a tedious t h a n t h e platinum method. When t h e bases weighed platinum dish, dried and weighed. Working are present as chlorides, there is not much difference with 5 t o IO mg. of K2PtCle, duplicates agree t o within in the amount of work required for each, except t h a t one wash solution less is used in t h e perchlorate method. about 0 . 2 or 0.3 mg. A Gooch crucible with a felt of specially prepared The solubility of KC104 in alcohol forms t h e chief asbestos, l / 4 in. thick, has given as good or better re- difficulty in obtaining accurate results. I n order t o use t h e perchlorate method t h e same sults in t h e hands of G. R. Stewart of this laboratory. I n this case t h e precipitate is weighed on t h e filter procedure is followed as for t h e platinum method t o without washing into a dish. The alundum crucible the point where t h e solution is ready t o be evaporated is a very satisfactory filter, when means are a t hand with platinum solution. If t h e solution contains so4 for giving it thorough washing. But it soon becomes it is removed by BaC12. Then the chloride solution blocked up by precipitated platinum so t h a t washing is evaporated with HC104 which expels HC1 and leaves all bases present as perchlorates; all of these are soluble is inefficient and filtration slow. The Munro Gooch with platinum felt is also good a t in alcohol except KC104, which is practically insoluble first, b u t rapidly gains weight due t o addition of re- in strong alcohol t h a t has been saturated with t h e duced platinum. This difficulty is found with all same salt. Absolute alcohol is t h e best wash as t h e forms of the asbestos filter. After considerable use KC104 is almost insoluble in i t , but it is not so good a t h e asbestos becomes coated with platinum black, solvent for t h e other perchlorates which are t o be which, b y catalytic action, perhaps, precipitates more washed out of t h e KC104. The chief difficulty with a n d more platinum each time it is used. Eventually the use of 95 per cent alcohol saturated with KC104 a new filter must be prepared. T o show this, 1/2 g. as a wash is due t o variation in solubility of KC104 KsPtCle was placed on a Gooch with asbestos felt, with variation in temperature. When the temperature washed with alcohol, dried, weighed; t h e precipitate rises during use, t h e solubility increases and some of was washed out with hot water, evaporated dry a n d t h e precipitate is dissolved, causing a low result. again filtered on the same filter. This was repeated six If the wash is used a t a temperature much below t h a t times after which the KzPtCle recovered had lost a t which i t was saturated with KC1O4, the latter tends 0.0076 g., while t h e crucible had gained in weight t o go out of solution and become a part of t h e preo.oo5j g. Apparently most of t h e decomposition of cipitate, thus producing a high result. So t h e same K2PtC16 occurs during t h e drying due t o action of precipitate may gain or lose weight by repeated washalcohol. I n general more reliable results are obtained ing with t h e same wash solution of alcohol saturated if the weight of t h e precipitate is found by subtracting with KC104 according as t h e temperature a t time of the weight of t h e filter before use from t h e weight of use is above or below t h a t a t which it was saturated. the filter and precipitate, instead of using the weight Speed of washing also affects t h e result. The same of the filter after washing out t h e precipitate. wash percolating slowly through the filter is quite likely t o add t o the weight of t h e precipitate, while DRYING T H E KzPtCle After final washing it is usually directed t o dry t h e if drawn through rapidly by suction the precipitate precipitate a t 100 t o 105' C. There is very little may lose weight. Various other washes were tried besides g j per cent change in weight of t h e precipitate by heating below alcohol saturated with KC104. Alcohol nearly ab1 4 0 O . ~ One gram KzPtCle heated in t h e oven lost as solute (99 per cent) containing 0.2 per cent perchloric follows: acid is t h e most satisfactory. It seems t o have very 3 hrs. at 142' C..loss 0.03 per cent 1 hr. at 155O C.,loss 0 06 per cent little effect on KC104, but dissolves the other salts The time required for proper drying depends on t h e quite well. Alcohol 95 per cent saturated with KC104 temperature and nature of the filter. A Gooch with is somewhat improved by addition of 0 . 2 per cent ordinary asbestos felt is very nearly dry after HC104. More t h a n 0 . 2 per cent HCIOI increases t h e hr. at I I O t o 120' C., and one hour is sufficient. But KClO4 solubility too much. Alcohol of 97 per cent if the felt is very thick or t h e liquid not well sucked strength similarly treated is somewhat better t h a n out, more time is needed. 95 per cent, but has t h e same general effect. TIME N E E D E D F O R C O O L I N G FILTER BEFORE W E I G H I N G Potassium acetate added t o alcohol decreases the An ordinary Gooch weighing about I j g. does not solubility of KC104 in it. But as it is necessary t o reach constant weight in much less t h a n l1/* hr. after use as much as one per cent, this wash must be re-

512

T H E J O C R N A L O F I N D C S T R I A L A.VD E N G I N E E R I N G C H E M I S T R Y

moved by one containing less matter in solution, such as 97 per cent alcohol KC104; thus t h e method becomes cumbrous. During this study nearly I O O determinations were made on a solution of pure KCI. But few results were close t o theory; more were high t h a n low. Portions of 0.1 g. KC1 gave o.rSjo t o 0.19jo g. KC104 a t various times; theory requires 0.1882 g. KC104. Presence of NaC1 or of BaC12, as when used t o remove sod, tends t o give high results, b u t if entirely converted to perchlorates by repeated evaporation with excess of HClO4 and t h e precipitate well washed, they do not seriously interfere. Cost of perchloric acid is a considerable item in this method. I t is expensive and not easily recoverable. If t h e acid costs $4.00 per lb. a n d I O cc. are used for one determination, t h e cost is about $0.10. I n using t h e platinum method there is some loss of platinum, b u t most of it is easily recovered so t h a t t h e loss should not exceed $0.03 per determination. I n general it is likely t h a t a n y analyst having equal experience with both methods will obtain more accurate results with less time, labor a n d expense by t h e platinum method.

+

S U IdMA R Y

I-In making t h e solution of a material for t h e determination of potash, considerable variation in t h e following factors has b u t little effect on t h e result: volume of water used, vigor of boiling, time boiled, excess of ammonia, and time of standing after boiling but before filtering. Ammonium oxalate must not be added till after t h e solution has been made alkaline b y ammonia (which should not be added in excess), and if there is more t h a n enough PzOb present t o form insoluble compounds with t h e bases present, ammonium oxalate should not be used, because it increases t h e amount of P205 remaining in solution. I n order t o obtain a correct result when t h e solution contains much soluble PzO:, a special procedure is necessary-either addition of excess of calcium and reprecipitation, or larger dilution, as described in t h e text. This is because potash is occluded b y t h e gelatinous precipitate of the phosphates. The method of making t h e solution by extraction with hot water on a filter is preferable as it gives higher results a n d less impurities in t h e solution. For this extraction a tube filter is much more efficient t h a n t h e ordinary paper filter in a funnel. 11-The effects of time, clarity of filtrate and absorption of potash b y t h e filter are negligible with most materials under ordinary conditions. 111-In evaporation of t h e solution H2S04 may be added a t any time before dryness, preferably a t first. IV-Ignition of t h e residue is probably t h e chief source of low results in potash determinations. T o secure correct results t h e heating must be so gradual t h a t spattering, which is common, does not occur. About I O mg. of sugar added during t h e evaporation sometimes aids materially. Various other substances added t o assist burning or t o hinder spattering were not found very useful. I n order t o secure good burn-

Vol. 9 , No. 5

ing t h e heat must be kept below t h e fusing point of t h e salts till after t h e carbon is burned off. The final temperature need not be above a moderate red heat for a few minutes. Long heating near t h e fusion point of t h e salts causes loss of potash. A little SO4 remaining as bisulfate does no harm. I n case t h e residue is not easily burnt white, it is best t o dissolve in water a n d a little HC1 and filter out insoluble matter. I n many cases organic matter a n d ammonium salts may be conveniently removed by evaporation of t h e solution with aqua regia, TI-Solution of t h e residual salts after ignition is best accomplished b y adding a few cc. of dilute HC1 a n d heating, before adding much water. Iron compounds t h u s dissolve readily a n d C a S 0 4 dissolves on adding more water. Insoluble Si02 m a y be filtered out without loss of potash. VI-separation of KzPt C16 requires certain conditions for a n accurate result. Concentration of potassium a t time of adding platinum must be low enough S O t h a t no K2PtC16 is precipitated a t once. Free HzS04, ”03, or organic matter must not be present. T h e amount of platinum used should be only slightly in excess of t h a t necessary t o combine with all t h e potassium. Excess of HC1 is unimportant. Evaporation should cease while some free HC1 still remains; if evaporation is carried too far dilute HC1 should be added and t h e evaporation repeated. YII-Purification of KzPtC16 is usually completed b y j or 6 successive washings, with I O cc. of t h e wash fluids. Effects of various strengths of alcohol, and of other wash fluids, and of many impurities in t h e precipitate are discussed in t h e text. Potassium is better separated from large amounts of sodium as cobaltinitrite t h a n as platinichloride. 17111-As a filter for collecting a n d purifying KzPtCls a n ordinary Gooch crucible with asbestos felt is most suitable a n d reliable for accurate work. A filter t u b e is somewhat more convenient b u t less accurate. IX-Drying of t h e K2PtC16precipitate may be done a t any temperature between I O O a n d 140’ C., a n d is usually complete in a n hour a t 1 2 0 ’ C. X-Weighing t h e crucible and precipitate should not be done in less than half a n hour after removal from t h e oven. During this time i t should remain in a desiccator. X I- T h e Perchlorate M et h o d for t h e determination of potash was found less desirable t h a n t h e platin u m method. I t is longer, more difficult and more expensive as t o reagents. BIBLIOGRAPHY ( I ) Lindo (1881). “Original Method lor Potash Determination.” Chem. Kews, 44, i i , 86,9 i . 129. (2) Gladding (1885), “Improvement on Lindo Method,” U. S. Dept. of Agriculture, Division of Chemistry, Bull. 7, 38. (3) Sssociation of OfficialAgricultural Chemists (1886 to 19 14), Bulletins of Bur. of Chem., U. S. Dept. Agr., particularly the earlier work in Bulls.

12, 16, 19, 24, 28, si, ss, 45, 47, 49, 67, 81, go, 99, 106, 116, 1% 132, etc. (4) N. Robinson (1894), “Study of Lindo-Gladding Method,” J. Am. Chem. SOC.,16, 364. (5) A. L, Winton (1895). “Proper Conditions for Determination of Potash, Suitable Concentration at Time of Adding Platinum.” J. Am. Chem. SOL.,17, 453.

May, 1917

T H E J O U R N A L O F I N D U S T R I A L A ,V D E iVGI N E E RI X G C H E .MIS T R Y

( 6 ) W. E. Garrigues (1895). “Claims that 90 Per cent Alcohol Precipitates NHiCl from Gladding Wash,” J. A m . Chem. S O L . , 17, 50. (7) R. De Roode (1895), “Recommends Aqua Regia Method for Purifying Potash Solution and Removal of NH4 Salts without Ignition or HzSOd.” J . A m . Chem. SOL.,17, 46, 86. (8) H. W. Wiley (1897), “Method for Determination of KzO and PzOr in Fodders, etc.,” J . A m . Chem. SOL.,19, 320. (9) C. C. hloore (1898), “Use of Acid Alcohol for Purifying KzPtCla,” J . A m . Chem. Soc., 20, 340. Also see Crookes “Select Methods,” p. 32. (IO) Winton and Wheeler (1898), “Study of Effect of “4C1,” J . Am. Chem. SOL.,20, 597. p (11) F. S. Shiver (1899), “Determination of Potassium as Perchlorate, etc., and Preparation of Perchloric Acid,” J. A m . Chem. Soc.. 21, 33. (12) C. L. Hare (1903), “Use of Ca(0H)z instead of Ammonia and Oxalate,” J . A m . Chem. Soc., 2 6 , 41i. (13) C. B. Williams (1903), “Use of HF to Decompose Soil for Determining K,” J . A m . Chem. SOL.,2 6 , 495. (14) E. M. East (1904), “Use of NarSOi to Remove Ba, Thus Avoiding Cse of NHa.” J . A m . Chem. SOC.,26, 297. (15) F. P . Veitch (1905). “Use of Acid Alcohol, etc.,” J . A m . Chem. Soc.. 27, 56. (16) Karl Regel (1906’1, “Difficulties Due to Sulfates. Estimates P t after Reduction by Mg,” Chem.-Ztg., 30, 684. (17) Wilcox, Buckley and Archibald (1908), “Solubility of KiPtCla in Alcohol of Various Strengths and in KCl and h7aC1,” J . A m . Chem. Soc.. 30, 749. 118) Breckenridge (1909), “Study of Causes of Low Results in Potash Determination by A. 0 . A. C. Method, Especially Effect of the Heavy Pre1 (1909), 409 and 804. cipitate by Ammonia and Oxalate,” THISJOURNAL, (19) T. E. Keitt (1913), “Study of Effect of Phosphates, ctc., in Potassium Determination,” Bull. 173, South Carolina Agricultural Experiment Station. (20) L. A . Hill (1903), “Colorimetric Determination of Potassium; Use of SnClr,” J. A m . Chem. Soc., 2 5 , 990. (21) Cameron and Failyer (1903), “Colorimetric Determination of Potassium, Use of K I on KzPtCla,” J. A m . Chem. SOC.,2 6 , 1063. (22) C. J. Schollenberger (191 l ) , “Effective Filter Tube,” THISJOURNAL, 4 (1912), 436. (23) W. A. Drushel (1O09), “Volumetric Cobaltinitrite hlethod,” 2. anorg. Chem., 61, No. 1, 137. (24) 0. M. Shedd (1910), “Study of Cobaltinitrite Method,” THIS JOURNAL, 2 (1910), 379. (25) L. T.Bowser (1911). “Qualitative Determination of Potassium as Cobaltinitrite,” J . A m . Chem. Soc., 33, 1566. “Quantitative Determination of Potassium as Cobaltinitrite by Titration of the Precipitate with KMnOd.” J . A m . Chem. SOC.,33, 1752. (26) A. H. Bennett (1916), “Use of Sodium Cobaltinitrite to Separate Potassium from Much Sodium,” A n a l y s t , 41, 165; Chem. Ahs., 10 (19161, 2334. (27) De Vries (1907), “Study of the Method and Various Sources of Error,” Chem. Weekblad., 4 , 231, (28) W B. Hicks (1913). “Reduces KiPtCla by Mg and Weight P t 6 (1913). 650. Formed,” THISJOURNAL, (29) Official Method of Association of Official Agricultural Chemists, U. S. Dept. A g r , Bureau Chemistry, Bull. 107, p. 11. (30) Same in J . 0.A . C . . 1 (1916). 12. DIVISIONO F AGRICULTURAL CHEMISTRY UNIVERSITY O F CALIFORNIA BERKELEY

THE FERTILIZER VALUE OF CITY WASTES 11-GARBAGE TANKAGE. ITS COMPOSITION; THE AVAILABILITY OF ITS NITROGEN, AND ITS USE AS A FERTILIZER’ By P. J. SCHROEDER

Among the various materials now obtained lrom city wastes. none has a greater importance as a fertilizer material t h a n garbage tankage.* I t s importance is far-reaching and is of concern t o every urban resident, for i t is necessary t h a t some disposition be made of material produced in such large quantities in every city, and it is of undoubted benefit t o every resident t h a t this be done with as little cost as possible to t h e city. Rendering for the recovery of grease and preparation of a fertilizer material is the method of disposal which Read before the Fertilizer Chemistry Section of the American Chemical Society a t Kansas City, Mo., April 10-14. 1917. * If considered on the tonnage basis, it may be necessary to make an exception of stable manure.

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possesses t o a greater extent t h a n any other the t w o most essential characteristics of any method of disposal, namely, economy and sanitation. The facts on which this statement is based will be presented in a subsequent communication. I t is obviously desirable t h a t the products obtained in this disposal be more generally understood, better appreciated and the fullest possible use made of t h e m in order t h a t they may bring as high a price as possible and t h a t their production be made as lucrative as possible so as t o bring the greatest return t o the community. I n the first paper of this series, “The Composition of Garbage,” the results of the analyses of zoo samples of raw city garbage were presented.’ The average of 7 j of the analyses, made of samples taken through a range of time covering a year, were as follows: Moisture, j 3 . j8 per cent; ash, 3 . 6 0 per cent; oil (ether extract). j .3 2 per cent; potash (K20). 0 . 2 j per cent; phosphoric acid ( P ? 0 5 ) . o 43 per c e n t ; nitrogen, 0 . 70 per c e n t , and combustible matter 22.63 per cent. METHODS O F R E S D E R I K G

For the recovery of grease, garbage is treated in three different ways: I-It is “tanked,” i. e . . cooked under pressure with steam, the water and liberated fats pressed out as completely as possible, and t h e oil separated from this by settling and skimming, the grease remaining in the solid residue after it has been dried being extracted with gasoline. 2-It is crushed t o render the particles uniform in size, dried directly in rotary, hot air kilns. the grease extracted with gasoline, and the solids ground for tankage. 3-It is heated with gasoline t o the boiling point of t h e latter, whereby the water contained is evaporated with the gasoline boiled off, while the grease is being extracted. The material is thus degreased and dehydrated in one operation and in one receptacle. I n some plants where the first-named process is in use, the dried tankage is not extracted with gasoline for the recovery of the grease still remaining therein, t h e operators contenting themselves with t h a t recovered by cooking and pressing. CHAR ACT E R A pi D C 0 MP 0 SIT10 li

Garbage tankage, then, is t h e solid residue when t h e water, the grease, and, generally, the water-soluble portions of garbage have been removed. From the foregoing paragraph it is seen t h a t by the first method mentioned the water-soluble ingredients are removed by cooking in steam and t h e subsequent pressing, while by the other two methods all the ingredients, except those volatilized b y drying and dissolved out by the gasoline, are conserved. I n some cases the aqueous solution pressed from the cooked material in t h e first-named process is evaporated for the recovery of its ingredients. The resulting concentrate is a sticky molasses-like substance known as “stick” and may be added t o the degreased tankage, which is 1

49-54.

W. J O’Brien and John R. Lindemuth, THIS JOURNAL, 9 (1917).