INDUSTRIAL A N D ENGINEERING CHEMISTRY
176
It will be noted from these data that, on the basis of the calculated values, the observed values of the molecular weights are 16.9 and 8.4 per cent less than the calculated values, in the cases of Chinese wood oil heated with rosin and ester gum, respectively-thus indicating that rosin is twice as good a
Vol. 17, N o . 2
retarding agent for Chinese wood oil as is ester gum. This is aIso in strict accordance with the common practical knowledge that twice as much ester gum as rosin is required in varnish-making sufficiently to retard the polymerization of Chinese wood oil.
The Analysis of Sodium Sulfide' By W. S. Calcott, F. L. English, and F. E. Downing E. I . D U
PONT DE
NEMOURS & CO.,WILMINOTON, DEL.
T
HE usual method of analysis of sodium sulfide, by de- subsequent storing and sampling of the material involved in an termining the total iodine absorption value of the Sam- extended investigation. Instead, sodium sulfide of the highple with subsequent correction for iodine-consuming est purity available was recrystallized from water as Na2S.impurities after removal of the sulfide as zinc sulfide, has been 9Hz0.immediately made up into stock solutions using freshly found untrustworthy, as the bulky gelatinous p-ecipitate of boiled distilled water, and stored in filled, tightly stoppered zinc sulfide readily absorbs v o l u m e t r i c flasks. If a the impurities present and series of analyses required The portions of sample used for the determination of handicaps the analyst in more than a day for comsodium sulfide and sodium thiosulfate are freed from the selection of a suitably pletion, the samples taken sodium sulfite by treatment with barium chloride. The sized sample. Results by each day were withdrawn sulfide is evolved as hydrogen sulfide, using ammonium this method tend to yield from a fresh flask of stock chloride which does not attack the thiosulfate, and is abhigh values f o r s o d i u m solution, or fresh samples sorbed in ammoniacal cadmium chloride solution, the sulfide and low values for were used and a re-analysis cadmium sulfide being titrated with iodine. The thiosulthe impurities. The followmade for comparison. Solufate is titrated with iodine after removal of the sulfide in a ing system of analysis has tions free from sodium sullarger sample by treatment with ammonium chloride and fite were obtained by using therefore been developed, evolution under reduced pressure. The sodium sulfite is sodium sulfide containing in which each principal condetermined by direct precipitation as barium sulfite in a considerable percentages of stituent of the material is medium of ammonium acetate solution made alkaline directly determined. sodium polysulfide, in which with ammonia, and subsequently titrated with standard sulfite is converted to soiodine solution. Sodium carbonate is precipitated as Determination of Sodium dium thiosulfate by reaction Sulfide barium carbonate under the conditions for the precipitawith the sulfur present. tion of barium sulfite. The acid-consuming value of the The ordinary procedure T h e effects of l a r g e precipitate is determined and the sodium carbonate conof determining sulfide by amounts of the impurifies tent calculated after deducting the equivalent acid-conevolution as hydrogen sul(sodium thiosulfate, sodium suming value of the sodium sulfite as previously deterfide with hydrochloric acid hydroxide, and sodium carmined by iodine titration. is not applicable to matebonate) upon the sodium The percentages of sodium sulfide, sodium thiosulfate, rials containing sulfite or sulfide determination are sodium sulfite, and sodium carbonate found in ordinary thiosulfate. Both these shown by the series of analsodium sulfide should be accurate to *0.3 per cent. impurities are decomposed yses of a sodium polysulfide by the acid treatment, with solution given in Table I. It is apparent from these results that the impurities, even &e evolution of sulfur dioxide, which reacts with hydrogen sulfide liberating sulfur, thus introducing serious errors into when present in large amounts, cause relatively small errors the sulfide analysis. The interference of sulfite may be over- in the sodium sulfide determination. come by its precipitation and removal as barium sulfite, but the interference of thiosulfate cannot readily be overcome so Table I-Effect of Added S o d i u m T h i o s u l f a t e S o d i u m Hydroxide. a n d S o d i u m Carbonate upon Determlnatio; of S o d i u m Sulfide long as the hydrogen sulfide is liberated by means of hydroAnalysis of stock solution chloric acid. It has been found, however, that hydrogen NazS No. Per cent sulfide is readily evolved by a mixture of ammonium chloride 1 18.OB and sodium chloride solutions, which form a medium not suffi2 18.20 3 17.99 ciently acid to decompose sodium thiosulfate appreciably.2 Average 18.08 ' With these modifications, the evolution method for sodium Added sodpum thiosulfate = 30 per cent of NazS present sulfide furnishes an accurate direct method for the estimation NazS NazS Difference found present of sulfide in the presence of considerable amounts of sodium Per cent Per cent Per cent No. sulfite and sodium thiosulfate. -0.2s 17.80 1 18.08 -0.18 17.90 2 18.08 EXPERIMENTAL-The preparation of sodium sulfide ab-0.18 17.90 18.08 3 solutely free from impurities such as sodium sulfide and sodium Added sodium hvdroxide = 60 aer cent of NazS present thiosulfate was not attempted, owing to the difficulties in18.05 -0.03 1 18.08 -0.00 17.99 18.08 2 volved in avoiding oxidation during preparation and in the +0.03 18.11 18.08 3 Received August 14, 1924. essential to the system of analysis was made at this laboratory by George Barnhart. 1
* This discovery
1 2
,Added sodium carbonate = 30 per cent of NazS pvesent 17.SO -0.28 18.08 17,99 -0.09 18.08
February, 1925
INDUETRIAL AND ENGINEERING CHEMISTRY
The presence of sodium sulfite in sodium sulfide causes appreciable errors in the analysis, as shown in the series of analyses given in Table 11. of Adged S o d i u m Sulfite upon D e t e r m i n a t i o n of S o d i u m Sulfide NazSOs added NazS NarS per cent of present found Error NazS present Per cent Per cent Per cent None 31.5
T a b l e 11-Effect
No. 1
...
None
j
...
31 3
-3 -6
5
7
It is evident that sulfite causes an appreciable error in the sulfide determination. To eliminate the effect of sulfite, the procedure of removing it from the sample by precipitating as barium sulfite was adopted. A stock solution of crystalline 32 per cent sodium sulfide was prepared by dissolving 125 grams in 1 liter of water; 200-cc. aliquots of this solution were transferred to 500-cc. volumetric flasks, the desired reagents such as sodium sulfite or barium chloride (25 cc. of 10 per cent solution) added, the contents diluted to the mark with distilled water, and the flask tightly stoppered. Two procedures for the removal of the barium sulfite were used. The first was to allow the stoppered flasks to stand overnight and upon the following morning to pipet out aliquots of clear solution for analysis. In the second method the flasks were allowed to stand, with occasional shaking, for 2 hours; the barium sulfite and barium sulfate were then filtered off through asbestos, 1 gram of washed Super-filtchar being added to retain the finely divided precipitate. I n Table I11 are gilen the results obtained with and without added sodium sulfite. T a b l e 111 -Effect of t h e Removal of Sulfite b y B a r i u m Chloride upon D e t e r m i n a t i o n of S o d i u m Sulfide Effect of b a r i u m chlortde treatment 10 percent Sample BaClz soluMethod of NazS found 32 per cent tion added removal of cc precipitate Per cent No. NazS 31 9 1 A None Settling n 2 A 25.0 Settling
I,,
Effect of added suljte: 25 cc. 10 per cent BaClz added to each sample Sulfite added per cent of NarS Dresent 1 B None Settling 2 B 15.5 Settling 3 C None Filtration 32. f 4 24.5 C Filtration
K:: E:;
1
The barium chloride treatment thus successfully eliminates the error due to the presence of sulfite without affecting the accuracy of the sodium sulfide determination. The detailed procedure of analysis adopted for the modified evolution method follows. APP.4RATUS AND SPECIAL REAGENTS-For the evOhtiOn Of hydrogen sulfide a modification of the apparatus used for the determination of sulfur in iron and steel is used. It consists of a Knorr flask of 200 or 300 cc. capacity and a 250-cc. gas absorption bottle connected in series. For the titration of the cadmium sulfide a 750-cc. Erlenmeyer flask equipped with a rubber stopper is used. Ammoniacal cadmium chloride. A stock solution of the following strength is used: cadmium chloride, 60 grams; concentrated ammonia, 250 cc; distilled water, 250 cc. Ammonium chloride. 20 per cent aqueous solution. Sodium chloride. Saturated aqueous solution. PREPARATION O F SAMPLE-For 30 per cent sodium sulfide dissolve a 50- to 60-gram ,sample in recently boiled distilled
177
water and dilute to one liter in a volumetric flask. For 60 per cent sodium sulfide dissolve a 60- to 70-gram sample and dilute in a similar manner. Pipet a 400-cc. aliquot of the sample solution into a 500-cc. volumetric flask, add 25 cc. of 10 per cent barium chloride solution, dilute to the markwith distilled water, and immediately stopper the flask and shake thoroughly. Allow the flask to stand overnight, whenthebarium carbonate, barium sulfite, and barium sulfate will settle and clear aliquots of sulfite-free sample may be withdrawn. If desired the solution may be filtered tjhrough asbestos after 2 hours’ standing by adding approximately 1 gram of Super-filtchar or high-grade charcoal to retain the finely divided precipitate. The sodium sulfide and sodium thiosulfate determinations are made upon the sulfite-freed sample, while the original sample solution is reserved for the sulfite, sulfate, and carbonate determinations. PRocEDuRe-Pipet a 25-cc. aliquot of the 30 per cent sulfide sample (a 10-cc. aliquot of 60 per cent sulfide) into the Kjiorr flask. In the absorption bottle place 150 cc. of a solution made by adding 25 cc. of the stock ammoniacal cadmium chloride solution to 125 cc. of distilled water containing 2 or 3 cc. of concentrated ammonia. Make all connections in the apparatus gas-tight, coating the rubber joints with collodion if necessary. Run into the flask through the funnel tube 30 cc. of saturated sodium chloride solution and 10 cc. of 20 per cent ammonium chloride solution. Heat the flask gently until the greater part of the evolution has taken place, then gradually increase the heat until the contents of the flask boil vigorously. Continue the boiling until salt begins to crystallize out. At this point apply gentle suction to the absorption flask, remove the flame from the Knorr flask, and open the funnel stopcock. Sweep the flask for approximately 10 minutes. Filter off the cadmium sulfide according to the following procedure : Into an 8- or 10-cm. (3- or 4-inch) Buchner funnel press a filter paper large enough to extend up the sides of the funnel to the top (the filter paper may be conveniently shaped over the bottom of a beaker which just slips into the Buchner). On top of the paper place a layer of asbestos over the entire bottom of the funnel. Wash the cadmium sulfide several times with dilute (1 :6) ammonia water and finally with two small portions of distilled water to remove nearly all of the ammonia from the filter cake and paper. During filtration and washing do not allow the precipitate to suck dry, or it will form a hard cake difficult to dissolve in hydrochloric acid. In the 750-cc. Erlenmeyer flask place 250 cc. of the distilled water and 100 to 13U cc. (an excess of 20 to 30 cc.) of 0. 1 AT iodine solution. Rinse any cadmium sulfide clinging to the inlet tube of the absorption flask into this solution, using dilute hydrochloric acid. Add 50 ce. of concentrated hydrochloric acid and 1Occ.of a 0.3 per cent starch indicator solution to the solution in the Erlenmeyer flask and immediately add the cadmium sulfide, filter paper, and asbestos. Insert the rubber stopper and shake the solution vigorously, macerating the filter paper and dissolving all visible particles of cadmium sulfide. Rinse the stopper and sides of the flask, and titrate the excess iodine using 0.1 h’ thiosulfate solution. Determination of Sodium Thiosulfate
The estimation of sodium thiosulfate depends upon tke same principle adopted to avoid the effect of thiosulfate upon the sodium sulfide determination. The sulfite-free sample is added to a mixture of sodium and ammonium chloride solutions, the sulfide boiled off, and the thiosulfate remaining titrated with iodine. I n order to avoid low results caused by decomposition of the sodium thiosulfate, the sulfide is removed under reduced pressure, and the mixture is heated in a boiling water bath to prevent the temperature from rising above
INDUSTRIAL A N D ENGINEERING CHEMISTRY
178
100" C. Thiosulfate cannot be accurately determined by titrating the residue from the sodium sulfide determination, for two reasons. The amount present is too small, on account of the limited size of the sample, and in the last stages of the boiling, to insure complete removal of the sulfide, some decomposition of the thiosulfate takes place which, although it does not affect the sulfide determination, appreciably lowers the result for sodium thiosulfate. EXPERIMENTA-The procedure of eliminating the sulfide from the sample by treatment with ammonium chloride so that the sodium thiosulfate might be determined was first applied to sodium polysulfide solution in which sulfite was absent. Mixtures of sodium polysulfide with ammonium and sodium chloride were boiled at atmospheric pressure until salt began to separate. Titration of the residue consisting of sodium thiosulfate and free sulfur gave erratic results. Decomposition of a part of the sodium thiosulfate by this rigorous treatment was suspected, so the procedure was applied to 25-cc. portions of 0.1 N sodium thiosulfate solution. As the solutions became more concentrated by evaporation, decomposition with the separation of sulfur became evident. At the end of one-half hour's boiling, losses of from 9 to 15 per cent of the sodium thiosulfate were encounterd. Evaporations were then made under reduced pressure. The solutions were placed in suction flasks and were heated under a vacuum of 610 mm. (24 inches), using a boiling water bath. After evaporating the solutions until salt crystals appeared, a slight cloud of precipitated sulfur was found, but of the 19.7 cc. of 0.1 N sodium thiosulfate added in each case the losses were but 0.3 and 0.4 cc., respectively, or 1.5 to 2 per cent of the amount present. By testing the solution for sulfide with lead acetate paper from time to time during the evaporation, it was found that the sulfide was rapidly driven off and that evaporation to the point of salt separation was not necessak-y. With this modification practically quantitative recoveries of thiosulfate were obtained. A polysulfidesolution analyzed for thiosulfate gave 8.10 and 8.02 per cent NazSz03. Known amounts of sodium thiosulfate solution were added to aliquots of this polysulfide solution, and analyses again made, with the results given in Table IV. Table IV-Recovery of NazSzOs Added to S o d i u m Polysulfide 0.1 N 0.1 N NazSzOx NarSrOa added recovered No. Cc. cc REMARKS
;:
3 4
19.7 19 7
:.$ 1
1
Solution evaporated to NaCl crystals Evaporated to negative test with lead acetate papers
Vol. 17, No. 2
results given in Table V. Aliquots of sodium sulfide solution containing 25 grams of 32 per cent NazS were treated with 25 cc. of 10 per cent barium chloride solution, diluted to 500 cc. and allowed to settle overnight. Aliquots of the clear solution were then analyzed for sodium thiosulfate. It is apparent that the barium chloride treatment does not affectthe accuracy of the sodium thiosulfate determination for amounts up to 6-7 per cent NazSz03 (19-22 per cent of the NazS present). Added sulfite has no effect upon the thiosulfate results. PROCEDURE-Pipet a 50-cc. aliquot of the sample into a 500-cc. suction flask containing 50 cc. of 20 per cent ammonium chloride solution and 25 cc. of saturated sodium chloride solution. Stopper the flask, apply suction, and place the flask in a boiling water bath. After boiling for 15 minutes, test the vapor and solution in the flask for sulfide with lead acetate paper. Continue the boiling under reduced pressure until there is no indication of hydrogen sulfide in the vapor or solution. In opening the flask no distillate containing sulfide must be allowed to strike back from the suction line. Slowly pour the remaining solution into an excess of standard 0.1 N iodine solution and back-titrate with 0.1 N thiosulfate solution, adding starch solution as indicator. Determination of Sodium Sulfite
EXPERIMENTAL-The procedure for the determination of sodium sulfite and sodium thiosulfate in sodium sulfide usually given in the literature involves precipitation and removal of the sulfide, with subsequent determination of the impurities in the filtrate. Precipitations by zinc sulfate, ammoniacal zinc chloride and by shaking with freshly precipitated cadmium carbonate were investigated. The zinc sulfate tended to give a colloidal precipitate of the sulfide which partially eluded filtration, while attempts to use cadmium carbonate resulted in frequent cases of incomplete precipitation. The results obtained by precipitation with ammoniacal zinc chloride were the best of the three. The sulfite in the filtrate and washings was precipitated as barium sulfite andestimatediodimetrically This method applied to a sample of sodium polysulfide showed sulfite to be absent. The method was then checked by the addition of aliquots of standard sodium sulfite solution to the sample. To avoid formation of thiosulfate from the added sulfite, the standard sodium sulfite solution was added to water containing the ammoniacal zinc chloride reagent. An aliquot of the sample was then slowly added. The zinc sulfide was allowed to settle, filtered off, washed, and sulfite determined in the filtrate. The results obtained, together with determinations made without the addition of the sample, are given in Table VI.
.
Table V-Effect of Removal of Sulfite f r o m S o d i u m Sulfide by B a r i u m Chloride T r e a t m e n t u o n Determination of S o d i u m T h o s u l f ate Thiosulfate ----THIOSULFATE---added per cent Present Found No. of sample Per cent Per cent E f e d of baiium chlovide treatment Series A 1 None 1.73 1.73 2 5.07 6.80 6.70 Series B 1 None 1.26 1.26 2 1.48 2.74 2.74 sample Efecl of added NazS03. T w o per cent Nai.503 added on we% 1 or 6.25 per cent on weigh1 of NazS Present -d 1 None 1.26 1 26' 2 1.48 2.74 2.76
Table VI-Determination of S o d i u m Sulfite in S o d i u m Sulfide after Precipitation of t h e Sulfide -SODIUM SULFITEPresent Found No. Gram Gram Test of BaSOs precipalalion, NarS absent 1 0.1376 0.1338 2 0.1376 0.1361 Test of recovery of Na2SOa zn presence of 0.5 gram hTazSfreefrom sul$le 1 0.1376 0.0532 2 0,1376 0.0445 3 0,1376 0.0631 4 0.1376 0.0858
The accuracy of the method as applied to sodium sulfide, where sulfite present was removed by precipitation with barium chloride, was next tested. Samples of crystalline 32 per cent sodium sulfide containing less than 0.5 per cent sodium sulfite were used in these experiments. The effect of the barium Chloride treatment upon the recovery of added sodium thiosulfate and the effect of added sodium sulfite upon the recovery of sodium thiosulfate were determined, with the
These results indicated that the procedure gave erratic and low results. Direct precipitation of the sulfite as barium sulfite without removal of the sulfide was then attempted, the barium sulfite being estimated iodimetrically. Determinations were made upon samples of sodium sulfide and sodium sulfide with added sodium sulfite. The precipitates were allowed to form overnight, to avoid heating the solution. High results in poor
February, 1925
INDUSTRIAL A N D ENGINEERING CHEMISTRY
agreement were obtained, indicating contamination of the precipitate with barium sulfide. Dilute solutions of sodium sulfide are strongly alkaline, owing to hydrolysis of the sulfide. It was considered possible to avoid any precipitation of barium sulfide with the sulfite if the precipitating solution were made less alkaline. A buffer of ammonium chloride solution was considered sufficiently acid to promote decomposition of the sample and the formation of barium bisulfite. A solution of ammonium acetate made alkalime to phenolphthalein with ammonium hydroxide was found suitable. A series of analyses of sodiumsulfide withvarious added amounts of sodium sulfite is given in Table VII. of S o d i u m Sulfite-Effect of S o d i u m Sulfide (25 cc. of 20 per cent ammonium acetate solution used as buKer) --SODIUM SULFITE-Present Found Difference No. SAMPLE Gram Gram Gram I 1 Sulfide absent (standard NazSOs 0.0983 0.0892 0.0061 2 solution) 0.0953 0,0912 -0.0041 3 0.0953 0.0867 -0.0086 Per cent I1 1 Sodium sulfide without added 0.93 2 sulfite 1.13 3 1.52 1.18 1.19 1.17 Per cent Per cent I11 1 Sodium sulfide with 1.91 per 3.09 2.80 -0.29 2 cent added NazSOs 3.09 2.83 -0.26 3 3.09 2.88 -0.21 T a b l e VII-Determination
-
IV
1 Sodium sulfide with 19.06 2 per cent added NazSOa
20.25 20.25
20 28 19.75
f0.03
- 0.50
These results are considered satisfactory. In the experiments carried out in the absence of sulfide, the filtrates were acidified and tested for sulfite with iodine, but no test was obtained. The low recovery is considered due to oxidation of the sulfite upon standing. After trial of the procedures involving removal of the sulfide by precipitation, the following method involving direct p r e cipitation of the sulfite as barium sulfite was adopted. PROCEDURE-In a 500-cc. Erlenmeyer flask place 75 cc. of distilled water and 25 cc. of a 20 per cent ammonium acetate solution made distinctly alkaline to phenolphthalein by the addition of concentrated ammonium hydroaide. Pipet into this solution a 50- to 100-cc. aliquot (3 to 5 grams of the sample), slowly add 20 cc. of 10 per cent barium chloride solution, stopper the flask with a rubber stopper, and allow it to stand overnight. On the following morning filter off the precipitate on a large Gooch crucible containing a mat of fine asbestos. Wash the Erlenmeyer and Gooch thoroughly with successive small portions of distilled water; it is not necessary to transfer the precipitate to the Gooch quantitatively. Return the precipitate andmat to theErlenmeyerflask, rinsing the cruciblethoroughly. Dilute the contents of the flask to 250 cc. with water and add a drop of methyl red indicator. Make the solution acid by adding a few drops of dilute hydrochloric acid (1:lo), then immediately add 50 cc. of 0.1 N iodine solution and 25 cc. of concentrated hydrochloric acid. Stopper the Erlenmeyer with a rubber stopper and allow the mixture to stand in a bath of cold water, with occasional shaking, for 1 hour. Rinse the stopper and sides of the flask, add 5 cc. of 0.3 per cent starch indicator, and titrate the excess iodine with 0.1 N sodium thiosulfate solution. Determination of Sodium Carbonate
Direct precipitation of sodium carbonate as barium carbonate under the conditions adopted for the determination of sulfite was found to supply a suitable method of estimation for this impurity. EXPERIMENTAL-The analysis of a sample of high-grade 60 per cent sodium sulfide with and without added sodium
179
carbonate and sodium sulfite, given in Table VIII, typifies the results obtainable by this method of estimation of sodium carbonate. In spite of the handicap to accuracy involved in the double analysis, entirely satisfactory results are obtainable, which have been confirmed in the routine application of the method. of S o d i u m Sulfide f o r S o d i u m Carbonate OY carbonate NazSOs Sulfite and carNazCOa in bonate found, sample NazSOa calcd. as Sample NazCOa calcd as NazC03 found NazS found Per cent Per cent N o . Grams Percent Percent 1 2 5000 0.68 0.57 2.57 1.94 2 2,5000 0.68 0.57 2.441 AVERAGE 0.57 2.51 1.66 p e r ceiii added Ara?S03 a?id 2.04 p e r cent added NazCOs Sulfite NazSOs and carfound, bonate Sample NazSOa calcd. found, calcd NazCOs NazCOa NazS found Theory as NazC03 as NazCOs found theory No. Grams Per cent Per cent Per cent Per cent Per cent Per cent 1 2.5000 2.45 2.34 2.06 6 12 2 2 5000 2 47 2.34 2.08 6:041 4'01 3'98 AVERAGE2.07 6.08
Table VIII-Analysis
N o added sulfile
PRocEDuRE-Precipitate the sulfite, carbonate, and sulfate in a 50- to 100-cc. aliquot of the sample by the procedure given for the determination of suliite. I n this determination, however, freshly boiled distilled water must be used and the flasks swept 5 minutes with carbon dioxide-free air before stoppering and allowing to stand overnight. On thefollowing morning filter off the precipitate on a Gooch crucible, wash with water, transfer the precipitate back into the 500-cc. Erlenmeyer, and add 100 cc. of distilled water and 100 cc. of 0.1 N hydrochloric acid. Boil the solution 15 minutes to drive off carbon dioxide and sulfur dioxide, cool, and titrate the excess hydrochloric acid with 0.1 N sodium hydroxide, using methyl red indicator. Final Tests
After the development of direct methods of analysis for the iodine-consuming constituents of sodium sulfide, analyses of samples were made for sodium sulfide, sodium thiosulfate, and sodium sulfite, and the total of these results (expressed as sodium sulfide) was compared with the total iodine absorption value of the sample. Results in complete agreement were obtained; the series of analyses of two such samples follows in Table IX. Table IX-Comparison of Calculated Effect of Directly D e t e r m i n e d I o d i n e - C o n s u m i n g C o n s t i t u e n t s of S o d i u m Sulfide w i t h Actual Iodine C o n s u m p t i o n Value DETERMINATION Sample I Sample I1 Sodium sulfide (evolution method) 62.5 57.8 Sodium thiosulfate (expressed as N a 9 ) 0.36 1.67 Sodium sulfite (expressed as Na&) 0.32 0.50 Calculated iodine absorption value as NazS 63.2 60.0 Actual iodine abscrption value as NazS 63 1 60.1
A complete analysis of a sample of sodium sulfide was also carried out using the scheme of analysis just described. Water in the sample was determined by dehydrating large samples (50 to 80 grams) and collecting and determining the water driT-en off. The results obtained are given in Table X. Analysis of a S a m p l e of S o d i u m Sulfide Per cent odium sulfide, NazS 56.90 b o a u m sulfite, NazSOs 0.74 Sodium thiosulfate, NazSzOa 7.31 Sodium sulfate, NazSOA 1.33 Sodium carbonate, NazCOa 2.79 Sodium chloride, NaCl 3.74 Insoluble matter 0.27 27.30 Water 100.38
Table X-Complete -5'
-
By means of the foregoing methods of analysis it has been found possible to predict closely the composition of sodium polysulfide solutions from the analysis of the sodium sulfide solutions used in their preparation, a thing which could not be accomplished by any other method of analysis tried.
