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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 ENGFNEERING C H E M I S T R Y
found t o be a suitable quantity of the diluted syrup for the purpose. Experiments were then made in which t h e concentration of t h e syrup and subacetate solutions were varied. T h e results are shown in Table 11. T h e procedure adopted on t h e basis of these experiments will be described in the next paper. Applied to t h e same 24 syrups of t h e season of 1915 as were tested by M r . MacFarlane’s procedure, the Van Zoeren procedure gave results ranging from 4.8 t o 6.0. This range amounts t o 2 2 per cent of the mean (5.55) or 2 5 per cent of the minimum as against 30 per cent of the mean (4.70) or 35 per cent of the minimum for t h e LIacFarlane procedure. TABLE11-TITRAMETRIC EXFERIMEKTS WITH LEADSUBACETATE Range of lead numbers Density of Cc. syrup No. of I n per subacetate diluted syrups Actual cent of solution t o 100 cc. tested minimum 1.050 10 6 KO definite breaks 15 23 2.5-4.5 80 20 8 2.4-4.7 96 1.033 5 16 I n 5 instances no breaks 8 12 41 4.0-5.9 10 16 4.7-6.5 38
SUMMARY
I-Silver nitrate added t o maple syrup gives a white precipitate which darkens on standing. The precipitation of silver continues during a period of several hours. 2-Mercuric acetate added t o maple syrup produces a light yellow precipitate. 3-Alcohol produces a precipitate containing most of t h e calcium and potassium. 4-4 moderately successful a t t e m p t was made t o combine t h e advantages of t h e Winton and Canadian lead subacetate methods. 5-The Canadian lead precipitates from six syrups showed a lead content of 66.95 t o 69.62 per cent; average, 68.42. The precipitate from a composite of 54 syrups contained 69.41 per cent of lead, while t h a t from another mixed syrup contained 70.1 I per cent. 6-Titration of maple syrup with N,’jo silver nitrate ( I ) directly, using electrical resistance measurements t o detect the end-point, ( 2 ) after treatment with lead subacetate or alumina cream, using potassium chromate as indicator, yielded definite b a t not useful results. 7-Titration with uranyl acetate gave no useful results. 8-Titration with lead subacetate solutions using electrical resistance as indicator led t o a useful method of testing the syrup for purity, which is described in t h e next paper of t h e series. 9-A complete anaIysis of t h e ash of a composite of about sixty genuine syrups shows more chlorine and less phosphoric acid t h a n t h e analyses previously recorded. MACDONALD COLLEGE, QUEBEC, CANADA
A COMPARISON OF METHODS FOR THE DETERMINATION OF SOIL PHOSPHORUS By W. 0. ROBINSON Received August 7, 1915
Hillebrandl outlines the main points of this determination in t h e following statement: “ I t is some1
U. S. Geol. Survey, B d l . 422 (1910), 144.
Vol. 8, NO. 2
times possible to extract all the phosphorus from a rock b y simple digestion with nitric acid, b u t quite as often if not oftener this fails; hence t h e necessity of resorting t o one of t h e longer methods of extraction 9 x x . Whatever method is used, great care is required t o secure accurate results. ” This statement applies t o soils with t h e further complication t h a t organic matter is inlTariably present, sometimes in amounts large enough t o require special treatment. METHODS O F S O L U T I O N O F T H E S O I L
Washington1 and P r y Z have called attention t o the presence of apatite inclusions in quartz as affecting the determination of phosphoric acid. Protected in this way the apatite would not, of course, be soluble in acids other t h a n hydrofluoric. Further, there are many phosphate minerals such as variscite, wavellite, and xenotime, which, from the standpoint of determinative mineralogy, are classed as insoluble in acids. These minerals have not been reported as occurring in soils, b u t there is a possibility of it. F r y 3 cites a number of analyses showing t h a t in most cases the total phosphoric acid is not dissolved b y acid digestion: from 4 t o I O O per cent is extracted. Obviously a method of simple acid digestion will not be generally reliable when applied t o soils. F I S C H E R ’ S i t r ~ ~ ~ o ~ - F i s c h ehowever, r,~ has modified a n acid digestion method so t h a t it appears t o extract t h e entire amount of phosphorus. The salient feature of this process is a n intervening ignition between two acid treatments. Briefly t h e procedure is as follows: j-10 grams of soil are treated with 5 0 cc. of aqua regia in a covered quartz dish of appropriate capacity. After t h e action has ceased t h e cover is removed and the mass evaporated t o dryness. It is then ignited (ostensibly long enough t o destroy organic matter) and again treated with aqua regia, evaporated t o dryness and taken up with nitric acid. Fischer claims t h a t the process gives slightly higher results t h a n the fusion method,’ though he proves there is a n almost negligible amount of phosphorus left in the insoluble residue. He points out t h a t a larger sample can be conveniently used with his method t h a n with t h e fusion method, thereby securing a fairer sample of t h e soil. The author has tested this method on a variety of soils. T h e samples were well ground a n a mixed so t h a t b u t one gram was employed in each case. After the second aqua regia treatment, t h e mass was evaporated once with nitric acid, heated on the hot plate t o browning t o dehydrate t h e silica, then taken u p with the requisite amount of nitric acid. T h e results, and for comparison, those obtained by other methods, are given in Table I. Fair agreement is shown, considering t h e determina1 “The Chemical Analysis of Rocks,” Wiley & Sons, Xew York (1910), p . 162. 2 THISJOURNAL, 6 (1913), 664. 8 L O C . cit. 4 Intern. Mitt. J’. Bodenkunde, 2 (1913), 541. 6 Probably due to the difficulty of precipitating small amounts of ammonium phosphomolybdate in presence of much NaNOa in the fusion method since Cajn and Hostetter [ J . Soc. Chem. l a d . , 4 (1912), 2501 have shown t h a t aqueous solutions of NaNOs have a strong solvent effect on the phospbomolybdate when vanadium is present.
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
Feb., 1916
tion, a n d one method can be classed a s accurate as another. Mr. W. H. F r y , of this Bureau, kindly examined soils Nos. 2 7 a n d 3 1 a n d found t h a t approximately 0.8 per cent of No. 2 7 was made u p of quartz grains with apatite inclusions. Similarly about 0 .I per cent of t h e soil grains of No. 3 1 contained a p a t i t e inclusions. He further reported t h a t t h e insoluble resiTABLEI-COMPARISON
OF OF
DIFFERENT METHOnS
FUSION
Soil No. 25
NalCOa alone
27 28
o.iiG,io 0.10-0.11 0.11-0.11
29 30 3220
...
4.90
FOR THE D E T E R M I N A T I O N
PHOSPHORUS IN SOILS
Results in Percentages
PsO,
+
NaaCOa NaNOa
o.16~6.10 ... ... ...
5.12
WASHINGTON FISCHER’S METHOD METHOD 0.18-0.18 0.10-0.08 0.08-0.09 0.10-0.10 0.08-0.09 4.98-4.97
0.16-0.17 0.12-0.10 0.08-0.10 0.10-0.10 0.09-0.08 4.93
I49
ignition. Numerous experiments show t h a t t h e addition of magnesium nitrate, previous t o ignition, is unnecessary for t h e reason t h a t nitric acid dissolves enough bases t o hold t h e phosphoric acid during t h e ignition. I n t h e following experiments one gram of soil containing 0.04 per cent of phosphoric acid a n d 0 . 2 9 per cent organic matter was used. A known a m o u n t of phosphoric acid was added in each case. The mixture was evaporated with nitric acid a n d ignited. T h e results are shown in Table 11. TABLE 11-VOLATILIZATION OF PHOSPHORIC ACIDDURING IGNITION Grams PzOr Added amount in soil.. . . . . . . . . . . . 0.0104 0.0104 0.0304 0.0304 0.0106 0.0104 0.0301 0.0305 Foun ..............................
+-
When 0.5 gram of sugar was added t o t h e above mixture a n d t h e ignition hasty a n d attended with glowing, there was an apparent loss of from 3 0 t o 1 1 per cent of t h e phosphoric acid present.’ I n nearly a score of soil analyses made b y this method only a negligible trace of phosphorus has been detected in t h e p a r t of t h e soil insoluble in hydrofluoric a n d nitric acids. Sulfuric acid must not be used i n place of nitric acid in this method for fear of driving off phosphoric acid during t h e ignition or volatilization of t h e acid.
due of soil No. 2 5 showed b u t a single inclusion, which was apparently apatite b u t could not be absolutely identified. T h e fresh sample contained comparatively many inclusions. T h e evidence is, therefore, t h a t apatite inclusions in quartz do not escape solution b y this method. THE FUSION METHOD-The method Of fusing t h e soil with sodium carbonate is a standard one. It requires more attention t h a n t h e other methods a n d is subject t o one inherent error, a s previously pointed out, DISCUSSION i. e . , t h e solubility of small amounts of ammonium Where platinum dishes are not available or it is phosphomolybdate in aqueous solutions of iYaN08.I If t h e sesquioxides are in excess, t h e P205 can be pre- wished t o avoid t h e use of hydrofluoric acid, Fischer’s cipitated with t h e m a n d separation of t h e N a N 0 3 method of making t h e solution will be found satisfacThe evaporation from quartz or porcelain2 is made in t h a t way. This requires another operation tory. a n d except for very small percentages, is not neces- slow, it is true, b u t does not require t h e constant attention of t h e analyst. sary. I n many soils t h e silica separated from t h e fusion need To further test t h e efficiency of Fischer’s method not be driven off with H F , a n d t h e residue brought of solution t h e following experiment was tried: A into solution a n d added t o the main solution. T h e sample of variscite with a small amount of gangue silica, separated from 5 soils containing from 0.05 was ground fine a n d well mixed. Although t h e mineral t o 0 . 1 3 per cent PnOs, contained, in every case, a n in- is reported t o be insoluble i t is only comparatively sufficient amount of P205 t o weigh. If, however, so: 0 . 5 gram of t h e powdered mineral when boiled t h e soil contains comparatively large amounts of two hours with 3 0 cc. nitric acid a n d 5 cc. hydrochloric zirconium a n d titanium as well as phosphoric acid, acid gave I 2 . 8 0 per cent PZOG soluble in acids. T h e t h e separated silica m a y contain considerable phos- sample contained 2 5 . 9 8 per cent PzOs. T o I gram phorus. For the sake of precaution, therefore, in samples of soil containing 0.09 per cent Pzos, 0 . 0 1 4 2 every case t h e separated silica must be worked over. a n d 0.0800 gram of t h e powdered variscite were added. Soils high in organic matter must be previously I n t h e two portions there was 0.0046 a n d 0 . 0 2 1 7 burned with magnesium nitrate or evaporated with gram P206 present. Fischer’s method of solution nitric acid a n d ignited, taking care t o avoid glowing, gave 0.0047 a n d 0 . 0 2 1 8 gram. T h e solution of t h e before t h e y are fused. I n such cases a n d if graphite variscite was effected b y ignition as is indicated b y or other reducing substances be present, some oxi- Morse’s3 work. dizing material should be p u t in t h e flux t o insure I N F L U E N C E OF V A N A D I U M complete conversion of t h e phosphorus t o orthoT h e author has previously shown4 t h a t soils conphosphate. tain appreciable amounts of vanadium, running from WASHINGTON’S METHOD-In laboratories where plat- 0.01t o 0.08 per cent, a n d sometimes nearly as much i n u m evaporating dishes are available, Washington’s vanadium as phosphorus. Brearley a n d Ibbotson’ a n d method2 of making t h e solution is b y far t h e neatest. Cain a n d Hostettera have shown t h a t in case of steels With soils t h e sample must first be evaporated with 1 If phosphoric acid can be converted during ignition, to a form not nitric acid a n d ignited t o destroy organic matter a n d changed to ortho-phosphate by two evaporations with nitric acid, it is render t h e soil easier t o decompose. No phosphoric possible that some escaped precipitation in this way during the experiment. See Leavitt and LeClerc, J . Am. Chcm. SOC., SO (1908), 391, 617. acid is lost b y this procedure, provided i t is carried 2 The porcelain must be capable of standing the ignition. o u t in such a manner t h a t there is no glowing during * J . A m . Chem. Sac, 26 (1903). 280. 1 Vanadium
4
2
is ever present in soils. “The Chemical Analyses of Rocks,” Wiley & Sons, N. Y. (1910), p. 162.
6
6
U. S. Dept. Agr., Bull. 122 (professional paper), 1914. “The Analysis of Steel Works Material.” London (1902), p. 163. THISJOURNAL, 4 (1912), 250.
I jo
T H E J O C R N A L OF I Y D C S T R I A L A N D ENGINEERIYG C H E M I S T R Y
the vanadium has a tendency t o prevent the precipitation of phosphoric acid. The former state t h a t t h e phosphorus determinations in vanadium-bearing steels are lorn, notwithstanding the fact t h a t vanadium is precipitated and weighed with t h e phosphomolybdate. Cain and Hostetter propose t o precipitate t h e vanadium completely by co-precipitation with t h e phosphorus. They found t h a t about ten times as much phosphorus as vanadium should be present t o secure the complete precipitation of the latter. They show t h a t the presence of vanadium in the molybdate precipitate can easily be recognized on account of the orange or brick color of the precipitate. The solution is colored a deep straw and precipitation is delayed or entirely prevented. Using Woy's method of precipitation, one gram of soil containing 0 . 1 9 per cent P20j gave 0 . 1 2 and 0 . 1 6 per cent when o.oo2j gram of V 2 0 5 had been added, and when 0 . I gram TrpOj had been added no precipit a t e appeared after 48 hours' digestion. More reagents, further digestion and mechanical agitation produced a precipitation of 0 . 0 8 and 0 ~ 0 4per cent in other gram samples. I n the following experiments t h e final volume in Q-hich the precipitation was made contained j-7 per cent nitric acid b y weight or volume,l j per cent ammonium nitrate, and t o this was added I O cc. of nearly neutral ammonium molybdate.2 The precipitation took place a t 6 j '-70' and t h e liquid was digested for two hours. I t was cooled before filtering. Table I11 shows t h e results.
T'ol. 8 , NO.
2
with soil solutions containing known amounts of vanadium and phosphoric acid. Precipitation was made in 1 2 j cc. wide-mouth assay flasks closed with a rubber stopper. Precipitation was complete in ~j minutes. With these soil solutions t h e addition of sulfurous acid was not necessary: 0 . 0 8 gram of ferrous sulfate was present in all cases. The results are shown in Table 117. TABLE I\'-sHOWING
T H E SEPARATION O F l r A K A D I U M .4ND PHOSPHORIC A C I D B Y MEAKSOF FERROUS SULFATE
NO.
Grams VzOc present.. . . . . , . , Grams PsOs present.. . . . . . . , , Grams P2Oc f o u n d . . . . . , , . , . ,
1 0.0008 0,0058
2 3 4 5 0.0013 0.0028 0.0103 0.0153 0.0058 0.00.54 0,0062 0.0058 0.0057 0.0058 0.0052 0,0062 0.0058
By taking precaution t o make t h e precipitation of t h e phosphomolybdate complete b y means of comparatively large excesses of reagents, and b y digestion and mechanical agitation, the influence of t h e amount of vanadium ordinarily found in soil can be avoided without reducing t h e vanadium, provided t h e yellow precipitate is converted t o magnesium ammonium phosphate. The method of titrating t h e precipitate with standard alkali calls for conditions which are against complete precipitation' and even though a second precipitation be made there is still some vanadium present and the results are a p t t o be low. Should t h e liquid, after the addition of t h e ammonium molybdate, t u r n a strong straw color and t h e precipitation be not complete after a half hour's digestion, there is a n excess of vanadium present. I n such cases if longer digestion. etc., do n o t satisfy the analyst t h a t precipitation is complete, a known amount of phosphoric acid must be added TABLE 111-INFLUENCEOF VAKADIUXO N THE PRECIPITATIOK OF AMMONIUM and the digestion continued. I t is important, of course, PHOSPHOYOLYBDATE NO. 1 2 3 4 s not t o add too large a n amount of phosphoric acid Grams VzOa present.. , . , . . , . 0,0000 0.0010 0.0015 0.0025 0.0050 lest the accuracy of the subtracted amount be under Grams PzOj present.. , . . . . . , . 0.0018 0.0018 0.0018 0,0018 0.0018 Grams PzOj f o u n d . , . . , , , , . . . 0,0019 0,0019 0.0018 0,0020 0 . 0 0 1 0 suspicion. I n these as well as in all other determinations I K F L U E N C E O F T U K G S T E K A N D T I T A N I U X OK T H E P R E CIPITATION O F PHOSPHORUS described in this paper the yellow precipitate was Small amounts of tungsten and titanium* interfere dissolved in dilute ammonia and slowly precipitated with magnesia m i x t ~ r e , ~ enough strong ammonia with t h e determination of phosphorus in the usual added t o make t h e liquid from j-7. j per cent S H 3 way in the course of iron and steel analysis. With soils tungsten would not interfere unless i t and the beaker allowed t o stand three hours in a cool carried down phosphorus m7ith it when precipitated place with occasional stirring. In laboratories where precipitation b y shaking or b y acids in removing t h e silica. The effect of t h e mechanical stirring can be conveniently carried on, amounts of titanium usually found in soils is negligit h e method of Cain and Tucker4 for precipitating ble when t h e gravimetric method is employed. Titaphosphoric acid in presence of vanadium is both ac- nium is more difficult t o wash out of the yellow precurate and rapid. The vanadium salts are reduced cipitate t h a n the other bases. In steel analysis t o the vanadyi condition by means of ferrous sulfate titanium retards precipitation and in some cases may and sulfurous acid. I n this reduced condition vana- come down with the phosphomolybdate. dium is not carried down with t h e yellow precipitate. I S F L U E N C E O F V A S A D I C I I O K T H E P R E C I P I T A T I O X O F Reoxidation of the \-anadyl salts by nitric acid is preA 11RI 0 N I C 11 3Ih G S E SI U 111 P H 0 S P H A T E C. vented b y keeping the temperature from I j '-20' X composite precipitate of magnesium pyrophosCompleteness of t h e precipitation is assured by shak- phate from about 30 soils was tested for vanadium ing. and showed only the merest trace. Solutions conThe author has tried this method of separation taining o.oojo gram VpOj and 0 . 0 0 8 6 4 gram PSOS 1 L-itric acid, s p . gr. 142. is about 70 per cent HITOs. were treated n*ith magnesia mixture in the usual S e a r l y neutral ammonium molybdate is preferable for it keeps its manner and allowed t o stand 6 hours; 0 . 0 0 8 8 gram strength, and further, since, using this method of precipitation, the solution ?
is strong with nitric acid throughout t h e precipitation, there is less danger of absorption or occlusion of t h e bases. 3 Too large an excess is to be avoided: 2 cc. above t h e actual amount
required for precipitation in 100 cc. of liquid is sufficient. 4 THISJOCRNAL, 6 (1913), 647.
To avoid t h e influence of molybdic acid. J. 11. Camp, "Methods for t h e Commercial Sampling and Analysis of Alloy Steel," U. S. Steel Corporation, 1915, p . 2 8 ; J. W. Mellor, "A Treatise on Quantitative Inorganic Analysis," Vol. 1. p . 594, J. B. Lippin1
2
cott Co.. Phila., Pa.
Feb., 1916
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
P205was found. When t h e precipitation for t h e same amounts h a d stood 1 7 hours, however, there was a p parently o 0145 gram PzO6. F r o m these experiments it appears t h a t with t h e small amounts of vanadium a n d phosphorus occurring in soils, a satisfactory separation can be made with magnesia mixture provided t h e precipitate does not s t a n d more t h a n 3-4 hours. No experiments have been carried out on larger amounts. T H E NATVRE OF T H E MIXED YELLOW PRECIPITATE
I t was first assumed t h a t vanadium replaced t h e phosphorus in t h e yellow precipitate. Later consideration showed, however, t h a t this was unlikely, for the precipitation of vanadium is complete' when phosphoric acid in amounts somewhat less t h a n t e n times the amount of vanadic acid is present, a n d Brearley a n d Ibbotson have shown t h a t t h e results obtained b y weighing t h e yellow precipitate are low when vanadium is present. T o test this point mixtures of phosphoric a n d vanadic acids were precipitated under conditions outlined in Bull. I07 (revised) of t h e Bureau of Chemistry of this Department, a n d titrated with standard alkali. The results are given in Table V below. T A B L E V-SHOWIHG T ~ EACIDITYOF THE PHOSPHOMOLYBDATE PRECIPITATE OBTAIXED IN THE PRESENCE OF VANADIUM S O . 1 2 3 4 Grams PzOs present., , , , , , , . . . , , , 0.00432 0.00432 0.00432 0.00432 0,00125 0.00250 0 , 0 0 5 0 0 Grams V?Oa present, , . . , , . , , , , , , None Grams PIOSfound.. . . , . . . . . . . . . . 0.00432 0.00396 0.00337 0.00298
The latter determinations showed incomplete precipitation. The precipitation was made complete a n d the phosphorus coming down was estimated gravimetrically. The amount of phosphoric acid recovered was added t o t h a t found b y titration, making t h e final figures for Experiments 2 , 3 a n d 4: 0.0045, 0 . 0 0 4 j a n d 0.0'042, respectively. It t h u s appears t h a t t h e acidity of t h e yellow precipitate is npt increased b y t h e presence of vanadium a n d t h a t volumetric determinations of phosphorus in presence of vanadium are a p t t o be low. Apparently t h e vanadium replaces t h e molybdenum instead of t h e phosphorus as indicated b y Blum.2 CO1\IPOSITIOii
OF T H E FEATHERY PRECIPITATE
When t h e phosphomolybdate precipitate is dissolved in ammonia there is sometimes a white precipitate resembling ferric phosphate which fails t o dissolve. Hillebrand3 states t h a t this is a compound of phosphorus and recommends t h e addition of a small amount of citric acid or in case this fails t o dissolve i t , fusion with sodium carbonate. Hornberger4 finds this precipitate contains titanium a n d phosphorus. It may be ferric, titanium or aluminum phosphates a n d hydroxides or mixtures of these, depending on t h e composition of t h e solution. It is a combination of phosphorus with t h e above bases t h a t have been absorbed or not thoroughly washed away. If t h e solution is made sufficiently acid before t h e precipitation a n d nearly neutral ammonium molybdate added with stirring, one need not fear t h e formation of this precipitate
* L
Cain and Hostetter. LOG.c i l . J . A m . Chem. SOL.,SO (1908), 1858. U. S. Geol. Survey, Bull. 422 (1910). 145. Landw. Vers. Sta., 82 (1913), 299.
151
unless t h e concentration of phosphoric acid a n d bases is large. I n such cases a second precipitation is t h e most expedient procedure. One gram of soil from the Hawaiian Islands, containing 4.9j grams P205a n d large amounts of iron, aluminum a n d titanium, was precipitated in small volume without much stirring a n d t h e residue insoluble in ammonia set aside and analyzed. I t contained 0.0017 A1203, o.ooj8 Ti02 a n d 0.0016 Fe203, combined with phosphorus. Two precipitations on t h e same amount conducted in a like manner yielded a precipitate containing 0 . 0 0 0 4 TiOz, 0.0001 Fe203, no A1203 a n d a n almost negligible amount of phosphorus. The precipitate obtained from some American soils contained only a trace of titanium a n d was largely aluminum. T h e feathery precipitate deliberately obtained in small amounts from eight samples of soil weighed from 0.0004 t o o.ooo8 gram. I n three cases only did t h e precipitate of Mg2P207 obtained from t h e above precipitates exceed t h e blank determination a n d these b y 0.0001gram only. When precipitation of t h e phosphomolybdate is carried on in such a manner t h a t it does not adhere t o t h e sides of t h e beaker or flask a n d washing is thorough, t h e feathery precipitate can easily be avoided in soil determinations. COiiCLUSIONS
I-The fusion methods, Washington's method a n d Fischer's method, of treating t h e soil for t h e determinations of phosphorus, give accurate results. 11-Vanadium interferes with t h e phosphorus determinations in soils. This influence can be avoided b y reducing t h e vanadium with ferrous sulfate a n d precipitating a t low temperatures b y shaking. With soil solutions it is not necessary t o a d d sulfurous acid t o prevent t h e reoxidation of t h e vanadyl salt. The influence of vanadium is also avoided b y using t h e gravimetric method, provided precautions are taken f o r complete precipitation and t h e ammonium magnesium phosphate precipitate is not allowed t o s t a n d too long. 111-Tungsten a n d titanium do not interfere with t h e determination of phosphorus in soils, b y t h e gravimetric method, provided precautions are taken t o make t h e precipitation complete. IV-The composition of t h e feathery precipitate is dependent on t h e nature of t h e bases in t h e solution before precipitation. Proper precipitation a n d washing of t h e yellow precipitate prevents t h e formation of t h e feathery precipitate or reduces it t o a negligible amount. BUREAUO F SOILS. WASHINGTON, D. C
SOME NEW METHODS FOR THE ANALYSIS OF LIMESULFUR SOLUTIONS1 By ROBERTM. CHAPIN Received July 12, 1915 INTRODUCTORY
The important substances contained in lime-sulfur solutions are calcium polysulfides and calcium thio1
Published by permission of the Secretary of Agriculture
