T H E J O U R Y A L OF IiVD U S T R I A L A S D E-VGINEERING C H E M I S T R Y
650
give all its phosphorus to the solution by this method must be treated in a n appropriate manner, so that the acidity, concentration of ammonium nitrate, and total volume obtained are always the same as by the method of solution directed. Slight deviations from these conditions are, however, probably without significance. Assuming solution of the steel and partial neutralization t o have been made as directed, the solution is cooled to I j ot o 20' C., 5 cc. of a saturated solution of ferrous sulfate and two to three drops of concentrated sulfurous acid are added. After addition of 40 cc. of molybdate reagent the solution is shaken in a n efficient manner for I O minutes. The precipitate, after settling (which is quite rapid), is then filtered off, washed in the usual manner, and t i trated by the alkalimetric method. The following table gives results by this method on synthetic solutions made with B. S. standard acid open-hearth, basic open-hearth, and Bessemer steels, of varying phosphorus and carbon content, to which vanadium was added as sodium vanadate and chromium as chromium nitrate. The acid and alkali solutions used for titrations were standardized against B:S. standard steels No. 19n (A.0.H. 0 . 2 ) and No. ga (Bes. 0 . 2 renewal). The individual determinations in each series are single determinations only; the good agreement in all cases with the certificate values for phosphorus of the individual steels shows the reliability and accuracy of the method. ' The time required is practically that for determining phosphorus in an ordinary steel. BUREAUOF STANDARDS ~VASHISGTOS -__
~
_
_
A RAPID MODIFIED CHLORPLATINATE METHOD FOR THE ESTIMATION OF POTASSIUM' By
\V. B HICKS
Received June 27, 1913
H I S T 0R I CA L
Many attempts have been made in recent years to develop a short practical modification of the chlorplatinate method for the estimation of potassium. These have proceeded along three essentially different lines, all of which have sought to avoid the necessity of estimating other constituents than potassium and sodium chlorides before undertaking the precipitation of the potassium. The first two modifications, the shortened method of Fresenius and the LindoGladding method, are so u-ell kno7v-n that they need not be discussed here. I n the third modification the potassium solution is evaporated directly with chlorplatinic acid, the residue washed u-ith alcohol, the potassium chlorplatinate reduced and either the chlorine titrated or the platinum weighed. Although such a procedure has been the 5ubject of numerous investigations in Europe, it seems never t o have found its way into American literature Because of this fact, and the rapidity, reliability and practicability of this procedure. the author feels justified a t this time in directing atten1
Published by permission of the Director of the LT. S. Geological
S u n ey
Vol. 5 , No. 8
tion to this excellent method, and in presenting the results of experiments along this line. Finkener,I in 1866, first used a reduction method for the estimation of potassium. He evaporated the potassium solution with chlorplatinic acid, washed the residue first with alcohol and then with ammonium chloride solution, reduced the K,PtCl, by igniting in hydrogen, extract.ed the residue with water and weighed the KCl, obtaining excellent results in the presence of various other salts. In 1873 Mohr* proposed to precipitate, wash and dry potassium chlorplatinate in the usual way, then t o mix this precipitate x i t h sodium oxalate, ignite, leach out with water, acidify with acetic acid a n d titrate the chlorine, using .K,CrO, as indicator, De Konincks suggested, in 1881, to dissolve the potassium chlorplatinate in hot water, reduce with magnesium ribbon and titrate the chloride with silver nitrate solution. To avoid the formation of oxychlorides in the reduction with magnesium, Fabrei suggested the addition of a drop of sulfuric acid which should be neutralized by means of CaCO, previous t o the titration with AgNO,. Diamants preferred to reduce the cblorplatinate solution with zinc dust rather than magnesium, because under the conditions .no oxychlorides of zinc were formed. I n a second investigation on the subject, De Koninck6 effected the reduction of the chlorplatinate by warming the solution with calcium formate. Stolba7 proposed, in 1884, to reduce the K,PtCl, with amorphous silver. This reduction, according to Atterberg,8 proceeds too far and is not to be recommended. Many reduction methods in which platinum is weighed have been proposed. Thus Hilgardg reduced the K,PtCl, by heating, while MeisslIo and Vogel and HaefckeII effected the reduction by heating the precipitate contained in a porous Gooch crucible in a current of hydrogen. NeubauerI' substituted coal gas for hydrogen because it is more practical and gives equally good results. Sonstadt13 accomplished the reduction by heating the precipitate with mercury. In all cases after complete reduction the soluble salts were washed out and the platinum weighed. I n the wet way the oldest reduction method is that of Corenwinder and Contamine.14 According t o their procedure, the K,PtCl, dissolved in hot water is added to a boiling solution of sodium formate. This method is often slow and leaves adherent deposits on the walls of the vessel which are difficult t o remove according to Jean and Trillat,~swho proposed to reduce P o g g . Ann., 9, 637 (1866). Z . anal. Chem.. 12, 1 3 7 (1873). Ree. Uniu. des Mines, 9, S o . 2 (1SS1). 4 Chem. Z., 20, 5 0 2 (1896). 6 Ibid., 22, 99 (1898). 6 Ibid., 19, 901 (1895). 7 I b i d . , 8. 456 ( 1 8 8 4 ) . 8 Ibid., 22, 538 (1898). 9 Hilgard, Versuchsstatio%en. 42, 174 (1893). 10 .Meissl. Ibid., 42, 173 (1893). 11 Landw'. V e r s . - S f a . 47, , 109 (1896). 12 Z . anal. Chem.. 39, 481 (1900). 13 J . Chem. S o c . , 67, 984 (1895). 14 Bull. de la SOC. Indusfrielle du S o r d , 1879. 15 Bull. de la S O C Chim. . de Paris. [3] 7 , 2 2 8 (1892). 1
2
3
Aug., 1913
T H E J O U R S - I L OF I - Y D U S T R I . 4 L .4 2; D E S G I S E E R I -YG C H E -1iI5 1 R I-
the chlorplatinate by adding a few drops of formaldehyde to the solution made alkaline n-ith soda. This effects immediate reduction, the authors contend, and the platinum comes down in large flocks which are easy to wash. Warrenr used formic acid and ammonia to effect the reduction. I n 1867 Roussin and Cornoillea suggested the use of magnesium as a means of reduction in analytical chemistry, and later Scheiblers used the metal in the analysis of gold and platinum salts of organic bases. I n 1893 T'illiers and Borg4 adopted this means of reducing the chlorplatinate in the estimation of potassium, in which they added fragments of magnesium ribbon t o the solution slightly acidified with hydrochloric acid until reduction was complete. The platinum was then filtered off 'and weighed. A%tterberg,s in a series of investigations on the best means of reducing the chlorplatinate in which a large number of reducing agents were tried out, concluded t h a t magnesium, mercury and thioacetic acid are best suited for this purpose. Thioacetic acid gives a voluminous precipitate of platinum and is therefore best used only with small amounts of platinum. Mercury gives good results only when in considerable excess and in hot, concentrated solutions. Magnesium, on the other hand, gives equally good results under all conditions a n d is therefore preferable. Later, this method of estimating potassium has been the subject of investigations by Rege16 Grete7 and Fiechter.8 The question concerning what substances interfere with the determination of potassium by the proposed method is a n important one. Vogel and Haefckeg showed t h a t sulfates do not interfere, while Neubauer'O obtained good results in the presence of sodium, calcium and magnesium chlorides and sulfates and large quantities of sulfuric acid. AtterbergII determined potassium in the presence of iron and alumina after the addition of citric acid. Earlier Villiers and Borg,Iz working on known samples, obtained I O O per cent of potassium in the presence of sodium phosphate, sodium and aluminum sulfates, and sodium, calcium, magnesium and iron chlorides. The present investigation has confirmed the results of these authors and has slightly extended the list of non-interfering substances. As a matter of fact, the writer has found no salts which seriously affect the estimation of potassium by this method and it is possible t h a t aside from rubidium, caesium, ammonium and organic compounds, no substances do interfere with this determination. .MET H 0D
On the basis of the results in the literature cited 1
Chem. X e w s , 76. 256.
a
2. anal. Chem., 6 , 100 (1867).
Deutsch. Chem. Gesell. Ber,, 2, 295 (1869). Combt. rend., 118, 1524 (1893). 6 Chem. z., aa. 522 (1898);aa, 538 (18983. 6 I b i d . , SO, 684 (1906). 7 I b i d . , 34, 1040. 8 2 .anal. Chem.. SO. 629 (1911). Landw. Vers. S f a . ,41, 109 (1896). Z . anal. Chem., 39, 481 (1900). l 1 Chem. Zeit.. [2] Pa. 538 (1898). Compt. rend., 116, 1524 (1893). 3
65 1
above and of the outcome of experiments described below, the following' procedure is recommended for the estimation of potassium. The method is applicable in the presence of chlorides. sulfates, phosphates, nitrates, carbonates, borates and silicates, salts of sodium. barium. calcium, strontium, magnesium, iron and aluminum. and is especially suited for the estimation of potassium in potassium salts, salines and mixed fertilizers in which only the quantity- of potassium is desired, and also in organic fertilizers after an appropriate modification to remove ammonia and other organic bases which interfere with the determination. The method follows: Prepare the solution in the usual way, acidify slightly with hydrochloric acid, add chlorplatinic acid solution slightly in excess of that necessary for the complete precipitation of the potassium present and evaporate the solution on the steam bath t o a syrupy consistency, i. e . , until solidification occurs on cooling. Flood the cooled residue with a small quantity of alcohol of a t least 80 per cent strength, grind thoroughly with a pestle made by enlarging the end of a glass rod, and allow t o stand one-half hour. The alcoholic solution should be colored if an excess of chlorplatinic acid has been used. Pour the liquid through a small filter, using suction, and before adding more alcohol rub up the residue again with the pestle. N o w continue the washing by decantation with small portions of alcohol until the wash liquid becomes colorless. Three or four washings usually suffice. Transfer the precipitate to the filter and wash two or three times with alcohol. Dissolve the precipitate in hot water, washing i t through the filter into a beaker of convenient size. To the hot solution add about I cc. of concentrated HCl and approximately 0 .j gram magnesium ribbon (which has been preyiously washed in water) for every 0 . 2 gram' potassium present, stirring the solution and holding the magnesium a t the bottom of the beaker by means of a glass rod. When the magnesium has practically dissolved, add a few cubic centimeters of dilute hydrochloric acid and allow the flocculent platinum t o settle. The supernatant liquid should be perfectly clear and limpid like water if reduction is complete. To make sure add more magnesium, in which case the solution will darken if reduction be incomplete. Now add concentrated hydrochloric acid and boil to dissolve any basic salts, filter, wash thoroughly with hot water, ignite and weigh. From the weight of platinum thus obtained calculate the per cent of potassium. The writer carried out eight determinations in conjunction, filtering both the potassium chlorplatinate and platinum on paper, using a filter cone and suction pump, and finally igniting and weighing the platinum in porcelain crucibles. E X P E R I M E N T A L PART
To determine whether or not the common associates of potassium interfere with its estimation by the proposed method, three series of experiments were carried out: 1
Fiechter, Z . a d . Chem., 60, 632.
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 A V I S T R Y
652
( I ) Blankdeterminationsona number of salt solutions. ( 2 ) Determination of potassium in known samples in the presence of various other substances (3) Estimation of potassium in natural brines and salines with and m-ithout the removal of other constituents. For this purpose the following solutionswereprepared : ( I ) Chlorplatinic acid solution containing one gram of platinum in I O cc. of the solution. ( 2 ) Potassium chloride solutions whose potassium content was carefully determined b y repeated analysis. (3) Solutions of the following salts: NaC1, Na,SO,, CaCl,, BaCI,, SrCl,, MgCl,, AlCl,, Al,(SO,),, FeCl,, Na,HPO,, Na,B,O,, NaNO, and silicic acid. Baker's analyzed chemicals were used for the preparation of these solutions with the exception of calcium, magnesium and aluminum salts, sodium sulfate and silicic acid, of which solutions were specially prepared t o free them from p o t a 4 u m . Blank determinations were made on each of these solutions b y evaporating a definite quantity with chlorplatinic acid and proceeding according to the method described above for the estimation of potassium. In all cases no residue of K,PtCl, could be seen, but on washing the filter paper with hot water and reducing the filtrate with magnesium a few flocks of platinum were noticeable in some cases. The results of these blank determinations are given in Table I : TABLE I Weight Substance taken Gram taken NaC1.. . . . . . . . ... 0 . 2 NaZSO,.. . . . . . ... . . 0.3
No.
1 2 3
4
. . . CaCl2...... . . . . . . .. . AlC13. . . . . . . . . . . . . . Alz(SO&. . . . . . . . . . . . FeC13.. . . . . . . . . . . . . . N@B40i. . . . , . . . . . . . SrCl2.. . . . . . . . . . . . . . BaC12. . . . . . . , . . . . MgC12. , , . . . . . . . . . . . . Na2HP04.. . . . . . . . . . . NaNOa.. . . . . . . . . . . . . Silicic acid.. . . . . . . . . Boric acid . . . . . . . . . ,
5 6 7 8 9 10 11 12 13
, ,
,
{ NaCl . . . . . . . . . . . . . . . ,
l4
0.3 0.3 0.5 0.3 0.3 0.3 0.3 0.4
Platinum solution used cc. 1.0 0.5 0.3
4.0 0.5 0.5 2.0 0.5 0.5 0.5 0.5 0.5
0.5
0.5
5.0CC. 0.2 0.35
0.5
Weight of platinum obtained Gram None 0.0003 0.0002 0,0002 None None None None None 0.0003 None 0.0004 0.0003 0.0006 None
''O
It will be observed t h a t in no case is there more than a few tenths of a milligram of platinum. This trifling amount is t o be attributed t o small quantities of soluble chlorplatinates adhering t o the filter paper or t o traces of potassium in the salts themselves. I n the experiments on known samples the potassium chloride solutions used were first carefully analyzed with the results given below. The theoretical factors were employed in all cases in making the calculations : KCl solution Sol. taken No. Cc.
{ io"
K2PtCIa found Gram 0,6505 0.6514
....
KCI calculated from KzPtCla found Gram 0.1995 0.1998
.... ....
Platinum found Gram 0.2612 0,2616 0.2626 0.2623
KCl calculated from platinum found Gram
0.1995 0.1999 0,2006 0,2004
Definite quantities of potassium chloride solution and of other salts were mixed, evaporated with chlorplatinic acid, and the method prescribed above was followed. The results are given in Table 11: TABLEI1
So.
1
} }
,
o,1997
o'2005
Quantity of salts added Gram
Salts added
......
NaCI.
{ 0":; { ::; { .;:
2 Na2S04 3
CaC12 . . . . . . . . . .
0.2
:E
4 AlCk
[ 0.3
5 AIzjS04)a ..... 6 FeCls..
..
.. . . . . . .
{ ::; { ::;
.IE::;
7 N a ~ B 4 0 7 ... . . . . 8 SrC12... . . . . . .. . 9 BaClz ..... . . . . . .
(0.3 10.3
{ :::
10 hlgC1, ........ . . . 11
... . . .
Ka2HP04..
12 S a N 0 8 . .
... . . . . .
13 NaCI.. . . . . . . . . .
KCI calculated KCI from KCI taken Platinum platinum recovfound found ery Cc. Gram Gram Gram P e r c e n t 10 0.1997 0.2617 0.1999 100.1 10 0.1997 0.2622 0.2003 100.3 10 0.1997 0.2624 0.2004 100.4 10 0.1997 0.2615 0.1998 100.1 10 0.1997 0.2628 0.2007 100.5 10 0.1977 0.2620 0.2001 100.2 10 0.1997 0.2607 0,1992 99.8 10 0.1997 0.2606 0,1991 99.7 25 0,2005 0.2623 0.2004 100.0 25 0 , 2 0 0 5 0.2622 0.2003 99.9 10 0.1997 0.2617 0.1999 100.1 10 0.1977 0.2613 0.1996 100.0 10 0.1997 0,2623 0,2004 100.4 10 0.1997 0.2626 0.2006 100.5 25 0,2005 0.2626 0.2006 100.0 25 0 , 2 0 0 5 0.2627 0.2007 100.1 25 0,2005 0.2636 0.2014 100.4 25 0.2005 0.2631 0.2010 100.2 25 0.2005 0.2629 0.2008 100.2 25 0.2005 0.2626 0.2006 100.0 25 0,2005 0.2621 0.2002 99.9 25 0 , 2 0 0 5 0.2612 0.1995 99.5 25 0.2005 0.2611 0.1995 99.5 25 0.2005 0.2631 0.2010 100.2 25 0.2005 0.2637 0,2014 100.5 25 0,2005 0.2612 0.1995 99.5
-
10
0,1997 0.2608 0 1392
99.8
25 0 . 2 0 0 5 0.2635 0.2011 130.3 25 0.2005 0,2635 0,2011 100.3 25 0.2005 0.2618 0.2000 99.8 15 Solution x ( a ) . . . . 25 0.2005 0.2621 0,2002 99.9 (a)Solution x represents a mixture of t h e following substances: HzSO,,. XaCl, NazSO,, CaC12, MgC12. FeCls, AlC13, Na2B40, a n d Na2HP04. l4
{i:gzs:
Silicicacid"""
{E
The figures indicate t h a t the above-mentioned salts have practically no deleterious influence on the estimation of potassium, and that the method IS sufficiently accurate for all commercial purposes. I n Table 111 are given the results of a few analyses obtained in checking up routine work: TABLE I11
NO.
200
400
85 KCl average Gram
Vol. j,NO. 8
120
Total PlatKC1 soluble Sample salts K2PtClR inum calcuCharacter taken present found found lated KCI of sample Grams Gram Gram Gram Gram Per cent Earthy 2 , 0 0 0 0.189 O.OPO5 . . , . 0.02471.24(a) 2.000 0.189 . . . . 0.0318 0.0243 1,22 terial.. 2.0000.4320 0.1306 . . . . 0.0401 2.00(a) 2.0000,4320 , . . . 0,0505 0,03861.93 2.0000.1303 0.1644 . . . . 0.0506 2.53(a) 2 , 0 0 0 0,1303 . . . . 0,06700.0512 2.56 10.470.4782 . . . . 0.3139 0.2398 2.29 Brine., , , , . . 10.470,4782 . . . 0,31340.2394 2.29 10.470.4782 . . . 0.3123 0.2386 2.28 1 0 . 8 1 0,8765 , . . . 0,35930.2745 2.54 Brine.. .. 2.700.2191 , _ . 0.09440.0721 2.67(a) ( a ) A11 constituents except Na, K a n d M g chlorides previously removed.
{
.
.. . .
.
.
4
These experiments were carried out in connection with the "Potash Investigation" in the U. S. Geo--
group were the following: Rice cooked by the method described in the U. S. Department of Agriculture, Farmers’ Biilletin, KO. 256, page 38. Boyd’s banana food: in this case the directions on the tin were follosT-ed. Frame food, when the directions given by the Frame Food Co. were followed. Provost barley, prepared by Messrs. R. Robinson & Son, of Annan; 142 grams were added t o 1,136cc. boiling water, the whole kept boiling for I j minutes. Provost barley V. S. GEOLOGICAL SURVEY D. C. WASHINGTON, and oats, both of which are partially cooked before coming into the market: one part of barley was T H E CHEMICAL COMPOSITION O F COOKED VEGETABLE added t o six parts of oats and treated in a similar FOODS. PART I11 fashion to the previous. Plasmon arrowroot: 2 5 . 6 B y KATHARISEI. WILLIAMS. grams were made into a paste with 80 cc. of warm Received April 14, 1913 water, then 204 cc. more water added ; the whole boiled The investigations described in the following pages for 2 minutes with continual stirring. Banana flour: are a continuation of the work published in the J O W 1 2 . 7 grams made into a paste x i t h j o cc. water, nal o j the A m e r i c a % Chenzical Society, Vol. XXVI, No. then cooked for 20 minutes with the addition of I O O 3, March, 1904, and Vol. XXIX, KO. 4, April, 1907. cc. water. R e v a l e n t n arabica: when the directions The main object of this work was to gain information on the tin were follom-ed. regarding the composition of foods as served a t table. Asparagus belongs to neither class ; i t was already A good deal has been published as to the cornposicooked, being a bottled sample of “ L e Success” systion of foods, but mainly dealing with the analysis tem. P. Phillips, -4sperge ilrgeicteuil. Each bottle of the raw materials. The fresh, green vegetables contained eight heads of the vegetable ; the average were bought when in full seas’on: Borecole, also weight was 209 grams. the average volume of liquid called Scotch Kale or Curly Greens, in February, Enj 4 C C . per bottle. dive in March, Chicory in February, and the cereal LOSSES IT T H E P R O C E S S O F C O O K I N G V E G E T A B L E S foods purchased locally. To ascertain the loss of nutrients in the process of GENERAL PREPhRATIOh7 O F T H E SAMPLES USED cooking. the liquid t h a t was drained off from the The first consideration was t o obtain a sample of lyeighed substance was evaporated over a water bath, each food as it would be served a t table, therefore, in the solid obtained finally dried in an air bath a t a ternthe case of chicory, borecole, chestnuts, endive, a n d perature not exceeding I I O ’ C.; the dish was cooled in a celeriac, the usual refuse in the way of stems, leaves and desiccator, weighed, the residue reduced to a fine husks was removed before cooking; the percentage is powder, again weighed. and replaced in the air bath shown in Table 11. until the weight was constant. From the data obtained With the cereal foods described there is no refuse or the percentage of loss 11-ascalculated. Two determinawaste, either before or after cooking. The water used tions mere made in every case. for cooking was t h a t supplied b y the Bristol Water Table I shows the total solids in uncooked vegetaCompany, about 26’ of hardness, chiefly due to calcium carbonate. N o salt or sugar was added before ble foods, the percentage of that solid lost in cooking, the weight in grams, the percentage of protein and ash or during the cooking process. in the residue recovered from the liquid drained off METNODS O F COOKING from the cooked food ; these percentages were deterTwo classes of food are dealt with, a i z . : ( I ) Those mined by the methods described for the dry powder in which, on cooking in a n excess of water which is foods. finally drained off, loss of nutrients occur, and ( 2 ) TABLEI those which absorb water during this process and which D n mat- Loss in Percentages of loss ter in cooking Loss in suffer no such loss. raw food Percooking Class ].-This class contains such vegetables as Grams centage Grams Protein Ash soya beans, green flagorets, and butter beans which, Rice.. . . . . . . . . . 8 5 . 8 5 10.90 9.36 6 94 . , 9 30 47.65 4.43 10.59 5.36 after soaking in water for 1 2 hours, were cooked slowly Celeriac . . . . . . . . . . . . . Butter beans., . . , , . 8 5 . 9 5 9.61 8.25 28 20 5.54 in boiling water until tender, the process being stopped . . S5.46 8.53 i.29 26.16 17.05 , . 86.85 9.22 8.01 ... 13.39 when the skins commenced t o crack. Celeriac was . . . 43.12 9.77 4.21 54.18 7.08 first pared and cut into thin slices, then cooked in Chestnuts . . . .... . . .. , 4.95 18.25 0.90 42.50 12.05 boiling water for 30 minutes. Chicory, borecole and . . . . . . . 10.82 48.92 5.29 41.42 15.77 27.89 2.47 29.48 18.75 endive, after being washed, and the outer leaves and E n d i y e . . . . . . , . . . . . . . 8.Si The liquid in which the asparagus had been prehard stems removed, were kept in boiling water until tender. I n the case of chestnuts, the outer husk was served was found to contain 2.41 grams of solid on removed, the skin taken off after placing in boiling evaporation, 16.9 per cent of which was protein. water for 2 minutes, and the nuts then cooked until fit I t will be seen celeriac contains only 9.3 grams of for use. Unpolished rice, after washing, was shaken solid matter and the loss is 47.6 per cent or 4.4 in into boiling water and cooked until quite tender, grams; borecole loses 4 8 . 9 per cent of solid matter; Class I1.-The various specimens analyzed in this butter beans only lose 9.6;green flagorets, 8.5 per logical Survey, so that the results illustrate the agreement t h a t should be obtained in practice. The method recommends itself from the fact that i t is well adapted for the carrying out of a number of determinations simultaneously, i t is accurate, i t is rapid in that most associates of potassium do not interfere, and it requires a minimum quantity of chlorplatinic acid solution.
A -
, ,
,
, , , ,
,
,
