July, 1918
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
jo cc. with 9; per cent alcohol, filtered, and a n attempt made t o assay t h e filtrate b y t h e official method’ with t h e following results. These results are calculated t o t h e original extract. I-Following t h e method as given, z per cent of oils found. 2-Heating was carried on for only I min. (shaking a t 1 5 sec. intervals), 8 per cent oil found. 3-Heating was continued for only 45 sec., 8 per cent oil found. 4-Heating was continued for only 2 0 sec., 11 per cent oil found. ;-Heating was continued for 2 j sec., 8 per cent oil found. 6-Heating was continued for 2 0 sec. a n d t h e n t h e suction was continued for an additional I j sec. without heat, 9 per cent oil found. 7-Heating was continued for 2 0 sec. and t h e suction for a n additional I O sec. without heat, 9 per cent oil found. The writer’s experience with this method has been most unsatisfactory, even moderate agreement in duplicate determinations has never been attained. The method leaves too much t o chance. If t h e flask i s not disconnected from t h e suction t h e instant t h e last of the solvent is drawn off, there is B loss of oil, a n d we have not been able t o discover any means whereby we can be assured when this instant is a t hand. Steam distillation gives very good results for peppermint if one determines beforehand what per cent of oil can be recovered with t h e apparatus in blank experiments using known quantities of pure oil. The writer has found this recovery t o be 90 per cent, so t h a t t,he quantity of oil found is multiplied b y roo a n d divided b y 90 t o find t h e amount present i n ‘ t h e extract. Proceeding according t o t h e directions given for lemon a n d orange extracts for steam distillation t h e following results were obtained on a I O per cent nonalcoholic extract a n d on commercial extracts. TABLEIV Prepared Extracts Strength Found Per cent Per cent IO 10 Peppermint. 9.8 Peppermint. . . . . . . 10 Peppermint. 10 10
......
.
~-~
......
Commercial Extracts Found Per cent 11.0 12.8 7.2
~
CHEMICALLABORATORIES A N D COMPANY MCCORMICK BALTIMORF,,MARYLAND
-___
A CONTRIBUTION TO THE COMPOSITION O F LIME-
SULFUR SOLUTIONS2 By 0. B. WINTER
Received April 19, 1918
The principal constituents of lime-sulfur solutions are calcium polysulfides and calcium thiosulfate. Small amounts of calcium sulfate and possibly of calcium sulfite are also present, and t h e claim has been made t h a t t h e solutions may contain other compounds such as hydrogen sulfide, calcium hydrosul1 “Report of Com. on Methods of Analysis,” J . A . 0.A . c., p. 268. 2 This work was done in the chemical laboratory of the Michigan Agricultural College Experiment Station and t h e results are published with the permission of the Director.
539
fide, calcium hydroxyhydrosulfide, different calcium oxysulfides, free lime, a n d free sulfur. How much of each of these compounds is liable t o be present? It is t h e purpose of this paper t o discuss some of the work done in this laboratory which pertains t o t h e above question. HYDROGEN
SULFIDE,
Ca(SH)2.
HzS.
CALCIUM
CALCIUM
HYDROSULFIDE,
HYDROXYHYDROSULFIDE,
CaSHOH I n reviewing t h e literature on t h e composicion of lime-sulfur spray, it is interesting t o note t h e discussions on t h e theoretical composition of t h e solution, together with t h e absence (except in a few articles) of even an attempt t o prove t h e existence of certain of t h e compounds discussed. Divers and Shimidzul give detailed methods for preparing some of t h e abovementioned compounds and s t a t e some of their properties, b u t their work has nothing whatever t o do with a n ordinary lime-sulfur solution. RoarkZ discusses t h e possible existence of these compounds in a limesulfur solution, b u t does not give experimental proof of their presence. T a r t a r a n d Bradley3 conclude t h a t they are not present in appreciable amounts. Thompson and Whittier4 claim t h e presence of hydrosulfide sulfur a n d give experimental d a t a which they believe justifies their claim. Green‘ says, “We have, liowever, never been able t o detect definitely t h e presence of hydrosulfide or free sulfuretted hydrogen in limesulfur solutions.” I t may be possible t o prepare a lime-sulfur solution which contains hydrogen sulfide, calcium hydrosulfide, or calcium hydroxyhydrosulfide, b u t it has yet t o be shown conclusively t h a t any of these compounds are present in appreciable quantities i n a “straight”6 lime-sulfur solution either as a result of t h e preparation of t h e solution, or of hydrolysis or other action taking place during storage under normal conditions. It is also interesting t o note t h a t writers seem t o have different opinions regarding t h e chemical actions which t a k e place in lime-sulfur solutions, and for this reason literature is quite confusing in regard t o t h e formation of a n y of t h e above-mentioned compounds. For example, t h e action of water on a polysulfide is represented as follows b y different chemists: Divers and Shimidzu:7 Cas5 2H20 = Ca(SH)(OH) 3s Ca(SH)(OH) 202 H2S = CaSz03
+
+
+
Auld :8 Cas, zHzO = Ca(0H)Z (x- 1)s H2Sx = HZS Roark : 7 2CaS, z H 2 0 = Ca(SH)2
+
+
+
+ + HzS + 0 4- 2Hz0
+ HzS, + Ca(0H)Z + ~ S , - I
J . Chem. SOC.,411 (1884), 270-91. 2 J . A . 0. A C., [ l ] 1 (1915), 81. 3 THISJ O U ~ N A2L (1910), , 271-7. 4 Delaware Agricultural College Experiment Station, BUZZ. 105 (1914), 8. 5 Union of S. Africa Dept. of Agr., 3rd and 4th Report of the Director of Vet. Research, 1915, p. 179. 6 By a “straight” lime-sulfur solution is meant a solution prepared from ordinary commercial lime and sulfur t o which no foreign substance has been added, and which has stood for several days 1
7 LOG.
8
Git.
J.’Chem. Sac., [ l ] 107 (1915), 482.
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
5 40
Averitt:l Up to a certain dilution no decomposition takes place when freshly boiled; distilled water is added t o a lime-sulfur solution. A similar disagreement might be given for many of the other reactions which are supposed to take place in boiling, storing, or diluting a lime-sulfur solution. Experiments in this laboratory show t h a t any one of the compounds mentioned above (containing the SH radical) may be detected b y titrating an aliquot of the solution with standard iodine, determining the end-point by the disappearance of the yellow color, and by titrating an equal aliquot with the same solution determining the end-point with nitroprusside2 of sodium. When the polysulfide has been entirely decomposed the solution loses t h e yellow color, while the blue color of the nitroprusside of sodium remains as long as there is any sulfur present either in the form of a sulfide or in t h e form of any compound containing the (SH) radical. If the two above titrations agree, none of the above-mentioned compounds are present. The following two equations represent the reactions which undoubtedly take place: Cas,
+ Ca(SH)z + H2S + IZ =
+ Ca(SH)z + H2S + S, (Titrated to disappearance of yellow color) Cas, + Ca(SH)Z + H2S + 412 = 2Ca12 + S(, $ 3 ) + 4HI (Titrated with nitroprusCa12
side of sodium as indicator) One might anticipate t h a t t h e difference between the two titrations would be a measure of the amount of sulfur present other t h a n sulfides, but we have not been able t o prove this since the color end-point in the presence of a considerable quantity of a compound containing the (SH) radical does not appear sharp. However, the method is sufficiently accurate t o show the presence or absence of any of these compounds. It might be well t o state here t h a t other experiments have shown t h a t when compounds containing the (SH) radical are present in a solution, an aliquot titrated with standard zinc chloride, using nickel sulfate as indicator, is higher t h a n one titrated with standard hydrochloric acid, using methyl orange as indicator. This may be explained b y the following equations : Cas, Cas,
+ Ca(SH)2 + 3ZnClz = zCaC12 + ZnS, + aZnS + 2HCl + Ca(SH)2 + 4HC1 7 2CaClz + 3H2S 4S,-i
If any of the compounds referred t o above are formed in an ordinary lime-sulfur solution, they must A . 0 A . C., [ I ] 1 (1915), 69. I n titrating with nitroprusside of sodium as an indicator for sulfur Compounds, it is essential t h a t the indicator should not be added until the end-point is practically reached, since if the blue color 1s well developed i t is almost impossible t o change back t o a colorless solution. If necessary, a few extra samples should be titrated, and those with the persisting color discarded.
V O ~ IO, . NO. 7
be unstable in the presence of other existing compounds, since the two iodine titrations mentioned in a preceding paragraph agree in every “straight” lime-sulfur solution t h a t has been tested in this laboratory, whether prepared with a n excess of lime or sulfur, whether freshly boiled or of long standing, and whether concentrated or dilute. Therefore we believe t h a t none of the above-mentioned compounds exist in appreciable quantities in a “straight” lime-sulfur solution; and vice v e y s a , if the spray contains any of these compounds, which can easily be detected, it is not a “straight” lime-sulfur solution. F R E E LIME
RoarkJ makes the statement t h a t “While not more t h a n a trace of calcium hydroxide [Ca(OH)z] may be present in a freshly prepared lime-sulfur solution, i t is formed in appreciable amounts upon dilution, according t o the reaction Casj zH20 = Ca(OH)2 HzS 4s and would be present, therefore, in lime-sulfur solutions which had stood for some time a n d become partially decomposed.” He gives no proof of its actual existence. Thompson and Whittie? claim that, “Free calcium hydroxide may occur either from simple solution, where an excess of lime has been used, or i t may result from hydrolysis of the polysulfide.” They found “free lime present when the ratio of lime t o sulfur exceeded a certain definite figure, increasing in amount as this ratio increased until the limit of the solubility of calcium hydroxide was reached.” They say nothing about how long t h e solutions in which they found free lime had stood before making t h e analyses, and show no data t o prove the statement t h a t “free lime may result from the hydrolysis of t h e polysulfide.” Tartar and Bradley3 reported t h a t no free lime or only a trace was found b y them in lime-sulfur solutions. They say, “It appears t h a t if there is hydroxide in the freshly prepared solution it either unites with some of the sulfur already in combination t o form more polysulfide, or it unites directly with the polysulfide t o form oxysulfides which crystallize out of the more concentrated solutions.” Chapin4 says, “If originally made with an excess of lime or if not boiled long enough, excess of lime is a t first present in solution, but if such a preparation be allowed t o stand quietly and cool off in t h e cooking vat, the indications are t h a t the undissolved lime soon settles down, while t h e small amount of dissolved lime rapidly reacts with polysulfide according to equation IoCaSj 3Ca(OH)2 = 12CaSl Cas203 3H20
+
+
+
+
+
+
so t h a t in this case also, unless the.cooled solution is again stirred u p with the sediment, a plus reaction figure can never be present in the end”-in other words, no free lime can be present. Green5 claims
1.7. 3
LOC C i l . Delaware Agricultural College Expt. Sta., Bull 106 (1914), 11. 3 THISJOURNAL, 2 (1910) 273. 4 U. S. Dept. of Agr., Bull. 451 (1916), 13. 6 Union of S. Africa Dept. of Agr , 3rd and 4th Report of the Director of Vet Research, 1915, p. 180. 1
2
July, 1918
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
t h a t a trace of free lime is usually present but t h a t t h e amount is very small. I n view of t h e above apparent differences of opinion, a n a t t e m p t was made t o prove either the presence or absence of free lime in a n ordinary lime-sulfur solution. Two different methods have been used by analysts for determining the amount of free lime in a limesulfur solution. The one (Method 1)’ is by titrating with o . I i V hydrochloric acid, using methyl orange as indicator, a n d with 0 . I N ammoniacal zinc chloride solution using nickel sulfate as a n outside indicator. I n this method, t h e hydrochloric acid titration indicates t h e lime combined with sulfur as polysulfides plus t h e free lime, while t h e zinc chloride titration indicates only the former. The difference between t h e two titrations is a measure of the free lime. T h e other (Method l l ) zis by removing t h e free lime as calcium sulfate by means of magnesium sulfate solution (the magnesium being precipitated as magnesium hydroxide and filtered o u t ) . T h e solution is titrated with standard acid before and after the removal of the free lime. T h e difference between t h e two acid titratiofls is held by t h e authors t o be a measure of the free lime. T h e results recorded in Table I were obtained by these two methods on 10 cc. of lime-sulfur concentrates diluted t o zoo cc., of which I O CC. were taken for analysis:
were freshly prepared from materials containing an excess of sulfur. ( 2 ) T h a t Method I shows no free lime or only a trace in the commercial concentrates which had stood from one t o t e n years, some of which had undergone considerable oxidation, whereas Method I1 shows its presence in all of these samples. (3) T h a t both methods show free lime in Sample I , which had been recently prepared from materials containing an excess of lime, but t h a t Method I1 shows the larger amount. (4) T h a t Method I shows very little free lime in Sample J (Sample I after standing two days), whereas Method I1 shows more t h a n when first prepared. ( 5 ) T h a t when a given amount of free lime was added t o a sample in which neither method indicated its presence, making Sample K , Method I shows nearly all t h a t was added, while Method I1 shows slightly more t h a n t h e amount added. (6) T h a t while Method I shows no free lime in Sample L (Sample A after having been exposed t o t h e air for several hours and oxidation had begun), Method I1 shows its presence. From the above d a t a it is evident t h a t t h e two methods do not agree. Which is correct? When we consider t h e known facts t h a t hydrochloric acid reacts with calcium polysulfides and calcium hydroxide as follows: Cas, Ca(OH),
TABLEI ---Method
B....
c.... D....
E....
F.. . . . . . . G.... ...
B.... ..
L.....
J,.... K.... L..
...
8.60 8.40 40.35 12.65 18.38 17.98 17.43 12.80 23.43 23.26 10.80 8.40
I-------
8.65 8.40 40.25 12.65 18.40 17.96 17.48 12.82 23.00 23.20 8.70 8.40
0.0000
0.0012 0.0002 0,0059 0.0000
+ zHCl + zHCl
= CaCL = CaC12
+ HzS + S(,-I) + zHz0;
t h a t ammoniacal zinc chloride reacts with calcium polysulfide according t o the equation
SAMWE 0 . 1 N HCI 0 . 1 N ZnCln CaO cc. cc. G. No. A , . . .. . .
541
8.60 8.40 40.35 12.65 18.38 17.98 17.43 12.80 23.43 23.26 10.80 8.40
8.60 8.35 37.90 11.90 18.30 17.65 17.00 12.08 22.20 21.85 8.20 8.00
CaO G. 0.0000 0.0001 0.0069 0.0021 0.0002 0.0009 0.0012 0.0020 0.0034 0.0039 0.0092 0.0011
I n explanation of the above table, it may be well t o state t h a t Samples A and B were prepared in t h e laboratory using a n excess of sulfur and were analyzed soon after their preparation. Samples C to H, inclusive, were commercial concentrates which had stood in the laboratory from one t o ten years, of which some had pi-eviously been opened for analysis a n d a large amount of oxidation products had formed. Sample I was prepared in t h e laboratory using an excess of lime and analyzed immediately after its preparation. Sample J was the same as Sample I , except t h a t t h e analysis was made two days after its preparation. Sample K was t h e same as Sample A, except t h a t 0 . 0 0 6 2 g. of calcium oxide had been added in t h e form of lime water in diluting t o zoo cc. Sample L was t h e same as Sample -4 after it had been standing, exposed t o t h e air, for several hours, a n d oxidation had begun. From a study of this table i t will be noted: ( I ) T h a t neither of t h e two methods show an appreciable amount of free lime in Samples A and B, which
and t h a t in t h e presence of ammonium chloride, ammoniacal zinc chloride does not react with calcium hydroxide, i t seems impossible t h a t titrations made with hydrochloric acid and zinc chloride could agree in t h e presence of free lime. Further, when free lime was added t o a lime-sulfur solution, it was practically all accounted for by the difference between t h e abovementioned titrations immediately after the addition. Therefore t h e author contends t h a t Method I is accurate for determining free lime in a lime-sulfur solution. Since Method I , as given above, has been noted in literature and has been shown t o be accurate, i t seemed worth while t o investigate Method I1 more thoroughly. Concerning this method Thompson and Whittier‘ state t h a t when magnesium sulfate is added t o a lime-sulfur solution containing free calcium hydroxide, magnesium hydroxide is precipitated quantitatively and calcium sulfate formed, thus neutralizing t h e solution and affording a method for determining t h e free lime. From other sources in literature, i t is well known t h a t magnesium hydroxide is precipitated when a solution of calcium hydroxide is treated with magnesium sulfate. However, this reaction is hardly considered sufficiently complete for quantitative determinations, and too, magnesium2 salts react with sulfides, as follows:
1
THISJOURNAL, 2 (1910), 2i3.
1
2
Delaware Agricultural College Erpt. Sta., Bull. 105 (1914), 11.
2
Delaware Agricultural College Expt. Sta., Bull. 105 (1914), 11. Prescott and Johnson, “Qual. Chem Anal.,” 6th E d (1904), p. 215.
542
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
MgS04 +zNa2S
+ 2H20 =
+
+
Mg(OH), Na2S04 zNaSH Divers and Shimidzu, in an article on ‘‘Magnesiunl Hydrosulfide Solution and I t s Use in Chemico-Legal Cases as a Source of Hydrogen Sulfide,”’ state t h a t , “The poly(-penta)sulfide t h a t may be in solution is only very slightly decomposed even a t boiling heat,” thus indicating t h a t the polysulfide of magnesium is a stable compound. Therefore, it appears possible t h a t when a lime-sulfur solution is treated with magnesium sulfate, chemical action may t a k e place even if there is no free lime present. I n order t o throw more light on t h e above question, the precipitate which came down on adding magnesium sulfate was tested for t h e presence of sulfui-, and was found t o contain a small amount. This would indicate t h a t t h e magnesium sulfate acted on some sulfur compound. However, t h e precipitate was amorphous and i t seemed possible t h a t some of t h e lime-sulfur solution might have been occluded. Therefore t h e test was not considered conclusive. The samples of concentrates which formed a precipitate with magnesium sulfate were diluted for analyses, with a n d without t h e addition of magnesium sulfate. Some of these were titrated for monosulfide and thiosulfate sulfur with standard iodine solution determining t h e end-point by disappearance of color and also b y t h e use of nitroprusside of sodium. The following results were obtained: TABLE I1 I for Monosulfide -With MgSOa- -Without ColorSodium Colorless Solu- Nitroless SoluSOLN. tion prusside tion No. Cc. Cc. cc. I... 8.14 8.32 8.50 2... 25.60
26.35
27.63
MgSOaSodium Nitroprusside cc. 8.52 27.63
I for Thiosulfate
After After TitraTitrating Cot- ting CoIumn3 umn5 Ppt. cc. cc. Verylittle 7.05 7.05 7.05 Lost Much ........
These d a t a show t h a t when magnesium sulfate are added t o lime-sulfur solutions, some compound is formed which causes a blue color with nitroprusside of sodium after t h e polysulfides have been decomposed and t h e solution has become colorless; and t h a t t h e thiosulfate content remains t h e same. Since t h e solution is colorless b u t reacts with nitroprusside of sodium, it apparently contains a compound having the (SH) radical, e . g., hydrogen sulfide, calcium hydrosulfide, calcium hydroxyhydrosulfide, or t h e corresponding salts of magnesium. Others of t h e prepared solutions were titrated with hydrochloric acid and with zinc chloride, and t h e following results were obtained: TABLE111 With MgSOa ~~
SOLN. No.
D. . . . . . . . . . . . . . . . .
E................. F..................
G................. H
.................
0 . 1 A’ HC1 cc. 11.90 18.30 17.65 17.00 12.08
0.1 N
ZnClz cc. 12.12 18.40 17.70 17.20 12.40
Without iLlgsO4 0.1 N 0.1 N ZnCln cc. cc. 12.65 12.65 18.38 18.40 17.98 17.96 17.43 17.48 12.80 12.82
These data show t h a t t h e titration of t h e treated sample with standard hydrochloric acid is lower t h a n t h a t of t h e untreated. This indicates the loss of some calcium compound. I t also shows t h a t t h e titration of t h e treated sample with ammoniacal zinc 1J
. Chem. Soc., 46 (18841, 699.
Vol.
IO,
No. 7
chloride is slightly higher t h a n with hydrochloric acid. This also is significant. It indicates t h e formation of some new compound, and this compound must contain the (SH) radical. The I O cc. aliquots of a lime-sulfur solution which indicated no free lime b y Method I1 were placed in each of two I O O cc. graduated flasks. One of these ( a ) was diluted t o the mark with freshly boiled distilled water, and t o t h e other (6) was added a large excess of I O per cent magnesium sulfate solution and then also diluted t o t h e mark with freshly boiled distilled water. Both solutions were allowed t o stand ,about 1 2 hrs. The former remained perfectly clear, as was anticipated; t h e latter also remained clear for several minutes, then gradually became cloudy and b y t h e end of t h e 1 2 hrs. a large number of crystals had formed, which, on examination;under a polarizing microscope, were readily identified as calcium sulfate (CaSO4.2H20). These solutions were then analyzed and t h e following results were obtained: SAMPLE
a.............. b..............
Mono-S Gram 0.0302 0.0279
TABLEI V M(SH)n-S Gram 0.0000 0.0012
Thio-S Gram 0.0330 0.0333
Sulfide-S Gram 0.1505 0.1377
.
CaO Gram 0.0813 0,0154
I n t h e above table t h e samples were titrated with iodine t o t h e end-point determined b y disappearance of color and also t o t h e end-point determined by nitroprusside of sodium, and t h e difference between these two titrations was considered as sulfur in t h e form of compounds containing t h e ( S H ) radical and is indicated as M(SH)&. The results in this table show t h a t there was a slight loss in t h e monosulfide equivalent and in t h e polysulfide sulfur; t h a t t h e thiosulfate sulfur remained practically t h e same; t h a t a small amount of some compound containing t h e (SH) radical was formed; and t h a t there was a loss of about 81 per cent of t h e lime.‘ I n other words, they show t h a t a large amount of calcium h a d disappeared while t h e loss in t h e monosulfide equivalent, thiosulfate, and sulfide sulfur were comparatively small. A microscopic examination showed conclusively t h a t calcium sulfate was precipitated from t h e solutions. N o w t h e following calculations may be made: 0.0333 X
56 = 0.0291 g. CaO necessary to combine with 0.0333 g. 64 S in Thio-S
0.0279 X
E = 32
-
0.0488 g. CaO necessary t o combine with 0.0279 g. S in Mono-S.
TOTAL . 0 . 0 7 7 9 g . CaO
From these it will be seen t h a t there should be 0.0779 g. of CaO in t h e solution, while there are only 0 . 0 1 54 g. b y actual determination. Evidently magnesium has replaced some of t h e calcium, and t h e solution now also contains magnesium polysulfide and a small quantity of some compound containing t h e (SH) radical. These compounds were not present in t h e original solution and must have been formed b y t h e addition of t h e magnesium sulfate. I t will also be seen t h a t t h e length of Time the solution is allowed t o stand and t h e quantity of magnesium sulfate present are important factors in this reaction. And it appears t h a t t h e lower polysulfides, or possibly t h e oxy-
July, 1918
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
sulfides of calcium are acted on more readily t h a n t h e higher polysulfides, since solutions prepared by using a n excess of lime in which lower polysulfides a n d possibly oxysulfides a r e present, react more quickly and with a less concentrated solution of magnesium sulfate t h a n do those in which a n excess of sulfur is used and only t h e higher polysulfides are present. From these d a t a as well as those in Tables I, I1 and 111, we must conclude t h a t magnesium sulfate reacts with some compound in a lime-sulfur solution other t h a n free lime, and in some solutions, a t least, this compound is calcium polysulfide. ’ Therefore Method I1 cannot be considered accurate for determining free lime in a lime-sulfur solution. Having presented evidence which we believe is sufficient t o show t h a t Method I is an accurate measure of the free lime in a lime-sulfur solution, and t h a t Method I1 cannot be considered accurate for this work, a few more solutions were prepared using different proportions of lime and sulfur, and a few more concentrates were diluted with lime water. These were analyzed by the former method, some immediately and some after standing several days. The results, together with explanatory remarks, are found in Table V : TABLEV
N/10
No. Cc. l . . . . 20.17
N/10 ZnClz Cc. 20.17
CaO Gram 0.0000
z....
20.15
20.15
0.0000
29.90
29.50
0.0011
4 . . . . 30.00
30.00
0.0000
S.... 10.80
8.70 8.50
0.0059 0.0045
SAMPLE HCl
3.
.. .
6.... 10.10
..
27.95
24.29
0.0103
a,.. .
3.97
3.95
0.0000
7..
Remarks S : CaO = 3 : 1. Analyzed immediately after boiling Same as 1 after standing well stoppered for three days S : CaO = 1 : 1. Analyzed immediately after boiling Same as 3 after standing well stoppered for three days Sample K in Table I Same as 5 after standing well stoppered for three days Commercial concentrate diluted with lime water (0.0106 g . CaO) Same as 7 after standing exposed t o air for fourteen days
The results in Table V, similar t o those in Table I, are in accord with t h e contention t h a t free lime is present in a freshly boiled lime-sulfur solution prepared by using an excess of lime, b u t they are cont r a r y t o t h e contention t h a t free lime will remain in such a solution or t h a t it is formed by hydrolysis. The only conclusions t h a t can be drawn from the two tables are, t h a t the small amount of free lime which may be present immediately after preparing a limesulfur solution, gradually disappears on standing, and t h a t immediately after adding free lime t o a lime-sulfur solution nearly all t h e lime exists in the free state, but t h a t chemical action takes place slowly, and after some time all the free lime has entered into chemical combination. Therefore, the inference is t h a t the ordinary commercial lime-sulfur solution, either concentrated or dilute, does not contain an appreciable amount of free lime. FREE SULFUR
Thompson and Whittier1 show t h a t the residue which separates from a lime-sulfur solution prepared with a n excess of sulfur in a n atmosphere of nitrogen, filtered while hot and kept in a completely filled, tightly 1
Delaware Agricultural College Expt. Sta., Bull. 106 (1914), 20.
543
stoppered receptacle, is mainly free sulfur. Auld’ mentions the fact t h a t when a lime-sulfur so1u;ion was prepared in an atmosphere of nitrogen and a n excess of sulfur was used, a polysulfide was formed which analyzed t o be the pentasulfide or slightly higher, and t h a t on standing free sulfur separated out. He believes t h a t sulfur may exist as free sulfur in solution. Harris2 prepared the pentasulfide by simply using a reflux condenser, and free sulfur crystals were found by the author in some of his solutions after they had stood several years. T a r t a r and Bradley3 succeeded in extracting free sulfur from a lime-sulfur solution and found t h a t the quantity extracted gradually decreased with t h e increase of the time of extraction, b u t found no definite end-point. Ramsey‘ contends t h a t the so-called polysulfide sulfur is loosely combined and t h a t free sulfur exists in t h e solution. Green5 says, “We regard our d a t a as effectually disposing of the contentions both of Auld and Ramsey in regard t o loosely attached sulfur, and sulfur in solution.” He believes t h a t the polysulfide sulfur is firmly combined and t h a t there is no free sulfur in solution. Thompson and Whittier conclude from their work t h a t no sulfide lower t h a n t h e pentasulfide is formed and t h a t free sulfur is held in solution. During the progress of this investigation samples were prepared with and without the use of a reflux condenser, using a n excess of sulfur. Those with t h e condenser approximated t h e pentasulfide, while those without were lower. I n both cases, when the solutions were filtered while hot into flasks which were completely filled and well stoppered and t h e solutions allowed t o cool, crystals which proved t o be free sulfur separated out. Even when allowed t o coal before filtering and then kept as mentioned above, free sulfur separated out of the more concentrated solutions. Table VI gives the results of complete analyses on a solution prepared from materials containing a n excess of sulfur and kept the lengths of time indicated. The analyses were made on I O cc. aliquots of t h e diluted concentrate. Time of Sulfur standCrysing tals l A ( a ) . . Still None warm 1 B.. . 12 hrs. Few 1C 32days Many ( 4 ) This solution was had not cooled.
SOLN. No.
.. ....
TABLEVI Total Ratio Mono-S Thio-S S-S Total-S CaO S-S: Gram Gram Gram Gram Gram Mono-S 0.0441 0.0430 0.2153 0.2620 0.1188 1 :4.88 0.0445 0.0492 0.2148 0.2639 0.1212 1 :4.83 0.0444 0.0496 0.2110 0.2606 0.1211 1 : 4 . 7 6 less concentrated than the other two because i t
This table shows a loss in sulfur from the solution, and the loss lies in t h e polysulfide sulfur. The fact t h a t before the deposition of the sulfur, the ratio of the sulfide sulfur t o the monosulfide sulfur was less t h a n 5, and t h a t as more sulfur was deposited this ratio was lowered, makes i t appear t h a t the free sulfur deposited in these solutions probably came from t h e breaking down of the higher polysulfides and not from free sulfur in solution. However, whether this ex1
J. Chem. Soc., 107 (1915), 484.
Mich. Agr. Col. Exp. Sta., Tech. Bull. 6 (1911). 10. THISJOURNAL, 2 (1910), 274. J . Agr. Sci., [21 6 (1914). 194-201. 5 Union of S. Africa Dept. of Agr., 3rd and 4th Report of the Director of Vet. Research, 1915, p. 192. 2
8
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planation is satisfactory or not, apparently makes little difference, since free sulfur in such a solution would undoubtedly have properties similar t o those of sulfur loosely combined, as in the case of the higher polysulfides. OXYSULFIDES O F CALCIUM
Most lime-sulfur investigators agree t h a t when lime and sulfur are boiled in water, with the lime in excess of the ratio I : 2 . 2 8 , and the solution is allowed t o stand in a closed vessel, certain oxysulfides of calcium separate out. However, they do not agree exactly as t o t h e constitution of these compounds. It has been suggested t h a t they are not ordinary oxysulfides1 as carbon oxysulfide COS, uranium oxysulfide U202S, manganese oxysulfide MnZOS, etc., b u t t h a t they are compounds made u p of a calcium polysulfide and calcium oxide; and t h a t the chief difficulty in t h e question of their composition is t o determine what polysulfide enters into their structure and whether or not this polysulfide is constant. Undoubtedly the most important evidence concerning these oxysulfides has come from an investigation of the crystals themselves, even though the results of different analyses of these crystals do not agree as well as might be desired. Considering t h e facts t h a t no solvent has been found b y which t h e crystals can be purified b y recrystallization and t h a t they cannot even be washed entirely free from impurities, it is almost surprising t o find t h a t different chemists agree as well as they do on their composition and properties. However, since there are the above-mentioned difficulties in dealing with the crystals, it seemed advisable t o compare the work done along this line in this laboratory with t h a t of others. I n doing this, lime-sulfur solutions were prepared by taking one part of calcium oxide, one part of sulfur and five parts of water, boiling without a reflux condenser until the escaping vapor showed the presence of hydrogen sulfide, filtering while hot, and placing in well-stoppered flasks, some of which were filled completely while others were only partially filled. I n all cases orange-red needles separated, even when the flasks were completely filled, showing t h a t they were not dependent on the oxygen of the air for their formation, (In the more dilute solutions crystals formed only in the partially filled flasks.) Several batches of these crystals were purified by separating them from the mother liquor by filtering through hardened filter paper in a Gooch crucible, washing a few times with small amounts of cold water (IO' C , ) * a few times with small amounts of 9 5 per cent alcohol, several times with absolute alcohol, ether, carbon disulfide, and then with ether again. They were dried in a vacuum desiccator over calcium chloride. The crystals purified as given above had an orangered color. They were found t o be insoluble in and not decomposable by ether, petroleum ether, chloroform, carbon disulfide, carbon tetrachloride, pyridine, or absolute alcohol. They were decomposed b y hot and cold water, forming a solution similar in appear1
Ann., 1 1 4 (1884), 178.
T'ol.
IO,
Xo. 7
ance and reaction t o a dilute lime sulfur solution, and leaving a white, amorphous residue. When treated with 9 5 per cent alcohol, pyridine containing water, or with a small volume of cold water they were decomposed, forming a solution similar t o the above; but some of the crystals retained their original shape, losing only the orange-red color. On heating, t h e crystals were gradually decomposed, leaving a white substance which did not melt or burn. Under the microscope the smaller crystals appeared like orangered four-sided prisms with parallel cleavage. Between crossed Nicols, the extinction appeared parallel in one position and a t an angle of about 30' in another. The white amorphous residue, as well as t h e white crystal-shaped masses which remained after treating with cold water, was found to be calcium oxide. Samples of different batches of these crystals were analyzed by treating with sodium hydroxide solution, oxidizing with sodium peroxide, acidifying with hydrochloric acid, and then determining the total lime and total sulfur in the usual manner. The results are shown in Table VII: TABLEVI1 Total
No.
21.23
27.01
Per cent
1 .................
3 . ..................... 4 5 6
...................... Average
22.09 21.83 21.08 20.70
Total Ca Per cent 28.28 27.11 28.77 25.47 25.11 27.30
S
SAMPLE
...........
-
-
Ratio S/Ca 1.34 1.27 1.28 1.17 1.19 1.31 _ .
1.27
, From the above results i t is evident t h a t the molecules making u p the crystals contain as many atoms of sulfur as of calcium, since the theoretical ratio of sulfur to calcium in such a molecule is I . 2 j, which is almost identical with the average of the above determined ratios'. On titrating several water solutions of the crystals with standard iodine and comparing the end-point determined b y color with t h a t determined with nitroprusside of sodium, i t was found t h a t the two endpoints were the same, showing the absence of the (SH) radical, and therefore the absence of any of t h e compounds containing this radical. T h a t lime is set free when the crystals are decompoked with cold water is shown b y the following: Two samples of crystals were shaken in flasks completely filled with freshly boiled distilled water until decomposition was complete. The solutions were then filtered and aliquots titrated with 0 .I N hydrochloric acid and with 0 . I N zinc chloride. The following results were obtained:
TABLEVI11 SOLN. No.
..................... 2 ...................... 1
HC1 cc. 5.49 16.04
ZnCln cc. 2.80 7.95
CaO Gram 0.0075 0.0226
The general properties of these crystals seem t o indicate t h a t they are the Herschell'sl crystals described in the literature, and a partial analysis shows t h a t their percentage composition agrees with one of the formulas given b y Geuther:2 1
Ann., 224 (1884), 181-192. Ibid.
July, 1918
T H E J O L ’ R X A L O F I N D U 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
(zCaO.CaS3. I 1H20) as is shown by the following: TABLE IX Geuther’s formula-2CaO.CaSa. Percentage composition-Theory
Found
’
...... .......
11H20
Ca
Per cent 26.9 27.01
S
Per cent 21.6 21.23
It should be noted, however, t h a t one property is shown b y t h e mother liquor from which t h e crystals separate which is very difficult t o explain if the crystals in solution are considered as being compose‘d of calcium oxide in combination with calcium polysulfide. This is shown by t h e fact t h a t when aliquots of such a solution are titrated with standard hydrochloric acid, standard zinc chloride, and standard iodine, the three titrations agree. This will be seen in the following table where I O cc. of lime-sulfur concentrates containing the orange-red needles were diluted t o I O O cc. with freshly boiled distilled water and I O cc. aliquots were titrated. SAMPLS No.
..................... 2 ..................... 1
TABLEX 0 . 1 N HC1 cc. 19.00 18.65
0 . 1 N ZnCl:! cc. 18.95 18.70
0 1 iV I CC. 18.95 18.65
If t h e mother liquor from which the crystals separate contains in solution a compound which has for its formula 2 C a 0 . C a S 3 . ~ ~ H 2it0 , is difficult t o explain the above results, since hydrochloric acid, zinc chloride, and iodine could hardly give equal titrations on a solution containing the molecules mentioned. No attempt t o explain this will be made a t this time, but it should be emphasized t h a t whatever t h e explanation may be, t h e fact remains t h a t the three titrations do agree. SUMXARY
I-Compounds containing t h e (SH) radical, as hydrogen sulfide, calcium hydrosulfide, calcium hydroxyhydrosulfide, and the corresponding salts of other metals, may be detected in a lime-sulfur solution by comparing t h e titration of the solution with standard iodine t o t h e disappearance of the yellow color with t h a t when t h e end-point is determined by t h e use of nitroprusside of sodium. 11-A “straight” lime-sulfur solution does not contain an appreciable amount of any of the above-mentioned compounds.
I
111-The difference between the titrations of a “straight” lime-sulfur solution with standard hydrochloric acid and standard ammoniacal zinc chloride is a measure of the free lime in the solution. IT7-When a n excess of lime is used in the preparation of a lime-sulfur solution and the solution is freshly prepared, or when recently diluted with lime-water, i t contains iree lime; but on standing, the free lime gradually disappears. Therefore an ordinary limesulfur solution cannot contain free lime. V-When magnesium sulfate is added t o a limesulfur solution the following may be noted: ( I ) There is a slight decrease in the monosulfide sulfur and the sulfide sulfur contents. ( 2 ) The thiosulfate sulfur content remains practically constant. (3) The magnesium replaces part of the calcium forming magnesium polysulfide and under proper conditions calcium sulfate crystallizes out. (4) A compound containing the (SH) radical is formed. VI-The magnesium sulfate method for determining free lime in a lime-sulfur solution is inaccurate. VII-There appears t o be no free sulfur in a limesulfur solution, and the sulfur t h a t separates out on standing undoubtedly comes from the higher polysulfides. VIII-When a concentrated lime-sulfur solution is prepared with an excess of lime, orange-red needles separate out. The properties of these crystals indicate t h a t they are t h e same as those described in t h e literature as Herschel’s crystals, and as being composed of calcium oxide combined with calcium polysulfide. Their analysis agrees most closely with t h a t of Geuther, who gives for their formula t h e following: zCaO.CaSa.I I H ~ O . However, it seems improbable t h a t they exist in soIution in the form indicated by this formula. ACKNOWLEDGMENT
This work was suggested by Prof. A, J. Patten of this laboratory, and was carried out largely under his direction. I wish t o express my great appreciation for t h e continued interest manifested throughout and for his kind advice and criticism. MICHIGAN AGRICULTURAL COLLEGE
B y H. B . PULSIBER Received April 3, 1918
While investigating the determination of sulfur in iron and steel as briefly described in THISJ O V R X A L ,8 (1916), I I I j , the author was led t o make a few determinations by the evoiution method. After the several estimations with dilute acid, both direct and annealed, as recorded in t h e foIIowing columns, it was decided t o conclude the work with other series using concentrated hydrochloric acid.
EXPERIMENT STATION
EASTLANSING,MICHIGAN
LABORATORY AND PLANT
A STANDARD APPARATUS FOR THE DETERMINATION OF SULFUR IN IRON AND STEEL BY THE EVOLUTION METHOD
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The excellent results obtainable with hot concentrated acid have been reported almost since the inception of the method nearly a hundred years ago; but Williams,’ in 1 8 9 2 , was apparently the first one t o compare results and demonstrate t h a t concentrated acid would furnish far higher and more correct results t h a n dilute acid. During the years following, numerous investigators,2 both American and European, J . Eng. S O L .West. Penn., 8 (1892), 328. Z. angew, Chem., 6 (1893), 11; Schneider, Oestevv. Z. Berg. Hiillenw., 41 (18931, 365; Phillips, J. A m . Chem. Soc., 17 (1895), 891; Petrkn, Jew-Kontorets Annaler, 60 (1905), 187; Schulte, Stahl U . Eisen, 26 (1906), 985; Kinder, Zbid., 28 (1908), 249; Orthey, Z. angew. Chem., 2 1 (1908), 1359 and 1393. 1
* Schindler,
