A p r . , 1916
T H E J O C R N A L OF I N D C S T R I A L A N D ENGINEERILVG C H E M I S T R Y
comparing these results, it should be remembered t h a t the work of both Behrens and Johnson was upon t h e first sweat and t h a t the work presented in this paper was done upon t h e resweat. TARIS 111-COIPARISON
OF
(PERCENTAGES)CHAKGES IN THE FIRST THE RESWEAT FIRSTSWEAT CHANGES RESWEAT (JohnCHANGEF (Johnson) son) (Reh(Author) Upper Short rens) Leaves Midveins Leave., See. Leaves -0.11 -0.61 .... . . . . -0.19 -0.63 -2.02 .... . . . . -0.02 -0.12 -0.21 4-0.02 - 0 , 0 3 .... -0,2i 4-0.04 + 0 . 2 2 .... -0.69 -0.44 -0.31 -0.45 -0,99 -2.28 +l.SO .... .... +1.23 0 0 0 0 0 70.90 .... +0.87 +0.29 .... -0.98 -0,44 -0.70 -1.54 -0.28 - I O . 18 . . . . -2.53 ..,. -0.85
SWEAT
AND
T o t a l nitrogen.. . . . . . . . . . . . Protein (factor 6.25) . . . . . . . . Ammonia. . . . . . . . . . .... .... Nitric acid (N2Ob). . . Nicotine. . . . . . . . . . . .... Amides (factor 4 . 3 . . .... Ash.. . . . . . . . . . . . . . . . . . . . C r u d e fiber., . . , . . , . .... Ether extract Nitrogen-free extract, . . , . . t0.8i Reducing substances.. . . . . . . Organic matter . . . . . . . . . . . . . -11.11 Other nitrogenous m a t t e r . . . .... Starch, . . . . . . . . . . . . . . . . . . . .... Acids (reckoned a s lactic acid). . . . . . . . . . . . . . . . Organic non-volatile acid., (reckoned a s ma+ acid) . Acids volatile In steam (reckoned as butyric acid). ... Sulfuric xcid (as SOai.. . . . . . ...
....
....
....
f1.03 4-0.09
-2.32
....
....
.... ....
-0.73 $0.14
.... ....
.... -0.02
-3.18
...
...
+0.16 -0, O i
S U M 31A R Y
I-The greatest loss of dry matter during the resweating process occurs in t h e proteins, nicotine, ether extract and nitrogen-free extract. T h e total nitrogen. ammonia, nitric acid, and crude fiber show slight losses. 2--The amides and reducing substances show a n increase. 3-The changes during the resweat are quite similar t o those of t h e first sweating process. I t seems, therefore, t h a t t h e resweat is a. continuation of t h e first sweating process. The changes during t h e resweat seem t o be greater t h a n during t h e first sweat, b u t this is what we should expect because t h e resweating process is more severe. 4--The loss in protein nitrogen minus t h e gain in amide nitrogen is 0.06 per cent and this plus t h e loss in ammonia (0.09 per cent) and nitric acid nitrogen (0.18 per cent) equals 0 . 3 3 per cent. The total loss in nitrogen is 0.61 per cent. The difference between t h e total loss of nitrogen and the loss of nitrogen as nitric acid, ammonia, a n d amides (loss of protein nitrogen minus amide gain in nitrogen) is 0 . 2 8 per cent. I t appears from this t h a t t h e most of the nicotine which is lost, is lost by volatilization. This is in accord with the results of Garner.‘ j-It is evident t h a t a breaking down of proteins into amides occurs. From this we can readily see t h a t there is probably an enzyme present which is capable of breaking down the proteins. 6--Since t h e increase in amide nitrogen is not so great as t h e loss in protein nitrogen it suggests t h a t there may be present a ferment which breaks u p t h e amino acids, although no definite conclusions can be drawn. .i--The total loss of organic matter in t h e leaf samples was 1 1 . 1 1 per cent a n d in t h e midveins 2 . 3 2 per cent. Behrens2 reports a loss of 5.6 per cent.
’
W. W. Garner, “ T h e Relation of Nicotine to t h e Quality of Tobacco.” Bull. 141, P a r t I, B. P. I . , U.S,Dept. of Agric. J. Behrens, “Weitere Beitrage zui Kentniss der Tabakpflanze, VII, Die Fermentation.” Landw. Vers. Sia..43 (1904), 293.
339
8-The changes in t h e midveins are similar t o t h e changes in t h e leaf b u t are not nearly so great Acknowledgments are due particularly t o Dr. W m . Frear for suggesting t h e problem and for valuable suggestions and criticisms, and t o Dr. C. W. Stoddart for many helpful suggestions. DEPARTMENT O F AGRICULTURAL CHEXISTRY PENNSYLVANIA STATE COLLEGE STATE COLLEGE,PENNSYLVANIA
NEW METHODS FOR THE ANALYSIS OF LIME-SULFUR SOLUTIONS. 11-THE ESTIMATION OF “POLY-SULFUR”L By ROBERTM . CHAPIN Received Ndvember 11, 1915
Whatever may be the actual atomic grouping of sulfur in t h e various calcium polysulfides which constitute the important ingredient of lime-sulfur solutions, it is convenient t o discuss the combinations of t h e element as if it occurred therein in t w o distinct forms, namely, “mono-sulfur” and “poly-sulfur.” The general formula for these calcium polysulfides may then be expressed as C a ( m - S ) (p-S),. A previous paper2 on the analysis of lime-sulfur solutions has described among other things t h e estimation of mono-sulfur. I n continuation of the work a volumetric method now has been developed for t h e estimation of poly-sulfur with, apparently, a desirable degree of both accuracy and convenience. DESCRIPTIOK O F THE M E T H O D
+
T h a t t h e reaction S Na2S03 = S a 2 S 2 0 Bapplies t o t h e poly-sulfur of soluble polysulfides has long been known. The reaction Ca(m-S) ( p - S ) , yNa2S03 = C a s yNa2S203is t h e basis of t h e new method. Mono-sulfur is removed as zinc sulfide and excess of sulfite as insoluble strontium sulfite, after which thiosulfate is determined b y titration with iodine. From t h e total thiosulfate thus obtained must naturally be subtracted the thiosulfate originally present in the lime-sulfur solution. The detailed execution of the method is as follows: I n t o a mixture of I O cc. of a recently prepared I O per cent solution of C. P. anhydrous sodium sulfite and 2 0 cc. of A / j ammoniacal zinc chloride, contained in a zoo cc. Erlenmeyer flask, pipette I O cc. of a dilution of t h e sample containing 1 . j t o 2 . 0 per cent “sulfide sulfur.” Mix. wash down with about 2 j cc. water and place on t h e steam bath at full heat. At intervals of IO min. mix the contents of the flask and rinse down with a little hot water from a washbottle. After heating for 4 j min. with four intermediate mixings. remove from t h e heat, add 2 0 cc. of a IO per cent solution of crystallized strontium chloride, and mix well. Let settle for five minutes, then filter into a zjo cc. volumetric flask and wash with hot water. Cool in water t o room temperature, add 0 . j t o 1.0cc. of a I O per cent solution of crystallized disodium phosphate, make t o t h e mark, shake well and filter through a dry paper into a dry flask, first using about 2 0 cc. t o wet the paper, t h e runnings being discarded. To zoo cc. of the clear filtrate add
+
1
Published with t h e permission of the Secretary of Agriculture.
a
THISJ O C R N A L , 8 (1916). 151.
+
3 40
T H E JOl’RNAL O F I S D l - S T R I A L A N D ElYGIIiEERIXG CHEMISTRY
methyl red indicator, then, slowly, and with thorough mixing, a I O per cent solution of tartaric acid t o a permanent slight acid reaction. Add starch and tit r a t e with N j r o iodine. T h e whole process should be executed without intermediate delays. From t h e observed iodine titration subtract a blank of 0.10 cc., rnultiply t h e remainder b y 1 . 2 j t o convert t o t h e basis of I O cc. lime-sulfur solution: a n d from this figure subtract t h e “thiosulfate figure”l previously obtained. T h e resultant figure is t h e “poly-sulfur figure” of t h e lime-sulfur solution as diluted for analysis, t h a t is, it represents cubic centimeters of 3;I O iodine equivalent t o t h e poly-sulfur in I O cc. of diluted lime-sulfur in t h e ratio of I a t o m of iodine t o I of sulfur. From t h e titration “figures” mentioned in this and t h e previous paper are naturally calculable t h e percentages of t h e various forms of sulfur existing in t h e diluted lime-sulfur solution, according t o t h e following formu!as : Sulfide-acid figure X 0.0016035 X I O = per cent mono-sulfur Poly-sulfur figure X 0.003207 x I O = per cent polysulfur Thiosulfate figure X 0.006414 X I O = per cent thiosulfate sulfur. XIELPFCL S O T E S O S T H E E X E C U T I O S O F T H E M E T H O D
1-The
zinc solution is best prepared by dissolving about metal in some excess of hydrochloric acid, diluting to about 900 cc., adding sufficient concentrated ammonia t o obtain a clear solution, and then diluting to 1000 cc. The zinc solution is to be used in 50 to IOO per cent excess of the amount called for by the previously described “sulfideacid figure,” for the precipitated zinc hydroxide is relied upon to render filterable the finely divided strontium sulfite. a--In order to be certain that sufficient sodium sulfite is present it is well to measure in slightly different amounts in duplicate determinations, in which case the duplicates cannot check if sufficient sulfite has not been added. j-The volume of sodium phosphate solution is varied between 0.5 and 1.0 cc., depending on the amount of strontium sulfite which appears to have passed the first filter. Even if no precipitate is visible, this step must not be omitted. The non-appearance of a considerable precipitate of strontium phosphate would of course indicate an insufficient addition of strontium chloride. In the final filtration from the strontium phosphate a plaited filter may be used with considerable saving of time if the filtrate is repassed until perfectly clear. 4-Tartaric acid is known to promote liberation and decomposition of thiosulfuric acid far less rapidly than do mineral acids in equivalent excess, and is therefore much preferable. j-The necessity for subtraction of the blank from the observed iodine titration will be discussed in the experimental section of this paper. 6-Both mono-sulfur and poly-sulfur are calculated from titrations which must be corrected for the amount of thiosulfate originally present in the lime-sulfur solution. The accurate determination of thiosulfate therefore becomes a matter of much importance. In the experience of the writer, methods which involve aliquot filtration from precipitated mono-sulfur and poly-sulfur are prone t o yield somewhat low and irregular results, apparently owing t o adsorption of thiosulfate by precipitated sulfur and sulfides.2 The following method is therefore 1 THISJOURNAL, 8 (19161, 151. 6.537 g. of C. P.
2 Compare Thompson S t a . , Bull. 105, p. 7.
and Whittier, Delaware College -4gric. Exp.
TO[.8 . S O .4
advised for the determination of thiosulfate: Into 2 0 cc. of AT/5 ammoniacal zinc chloride contained in a 150 cc. beaker, pipette IO c?. of the diluted lime-sulfur solution. Mix, dilute to about 7j cc., heat on the steam bath 30 min. with occasional stirring, then filter and wash with hot water. Cool the filtrate, add about I g. C. P. potassium iodide, methyl red indicator, and cautiously render slightly acid with I O per cent tartaric acid, finally titrating with iodine. EXPERIXESTAL
T h e scheme a t first investigated was t o pipette t h e sample into a freshly boiled a n d hot solution of sodium sulfite a n d ammonia. boil a sufficient length of time, and t h e n t o add both ammoniacal zinc chloride a n d strontium chloride after which‘ t h e determination was completed as i n t h e regular method. This procedure is more rapid and b y the speed of decolorization indicates t o t h e eye vhether sufficient sulfite has been employed. T w o obvious objections are t h a t excess lime may react with some poly-sulfur, producing lorn results, and t h a t some mono-sulfur may become oxidized, producing high results. With t h e object of testing these sources of error t h e regular method prei-iously outlined m z s tried, without, it must be con.fessed, much hope t h a t t h e sodium sulfite would successfully perform its function upon precipitated poly-sulfur. When such was found t o be t h e case t h e first conceived method was abandoned, at least for t h e present. for in t h e regular method described t h e solution is alkaline with ammonia only. a n d all mono-sulfur is in t h e form of non-oxidizable zinc sulfide. E X P E R I X E N T I , following t h e regular method except in t h e m a t t e r of heating, indicates t h e speed of t h e reaction between sulfite and poly-sulfur. TEST
TIME HFATED No.OF MINUTES
MIXINGS
IOOIXll:
TITRATION
T h e results indicate t h a t t h e prescribed conditions make ample provision for solution of all poly-sulfur, provided t h e full heat of t h e steam b a t h is used. They further indicate t h a t properly executed duplicates will yield figures in satisfactory agreement. Since strontium sulfite could not be assumed t o be absolutely insoluble, it was necessary t o determine a blank for sulfite reaching t h e stage of iodine titration. E X P E R I X E N T z-Blanks r u n with j cc. of sodium sulfite solution gave 0.12 a n d 0.11 cc. -VI I O iodine. A blank r u n v i t h I O cc. sodium sulfite. using 30 cc. strontium chloride, gave 0.11 cc. iodine. I n each case about z g. C. P. potassium iodide Lvere added t o t h e filtrate before titration. Since t h e size of t h e blank was not affected b y t h e quantity of sodium sulfite used t h e blank titration must be attributed solely t o t h e solubility of strontium sulfite and not t o t h e presence of sodium thiosulfate as an impurity i n t h e sample of sodium sulfite employed. Remembering t h a t i n t h e execution of t h e method in practice no correction for t h e end point with starch is called for. since t h a t is automatically pro.iided through t h e necessity of subtracting t h e thiosulfate figure, it is fair t o set for t h e solubility of strontium
Apr., 1916
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
sulfite a correction of 0.10cc. N / I O iodine per 2 0 0 cc. filtrate. Incidentally it may be noted t h a t we have here t h e basis for a good practical method for estimating thiosulfate in t h e presence of sulfite. If, as t h e writer believes, t h e combined determination of mono-sulfur a n d poly-sulfur as described constitutes a method for t h e estimation of sulfide sulfur which is more accurate in practice t h a n a n y other previous method, i t is obviously impossible t o check t h e accuracy of t h e new nlethod b y comparing its results with those afforded b y other methods. B u t such a comparison is of importance for practical reasons a n d has been undertaken. EXPERIMENT 3-Taking t h e standard method' of t h e A. 0. A. C. as a basis, procedure was modified in accordance with facts regarding t h e estimation of sulfuric acid as barium sulfate brought out b y Allen a n d Johnston12 a n d b y Walter Allen a n d B i ~ h o p . ~Using I O cc. of t h e diluted sample, sulfide sulfur was separated b y ammoniacal zinc in t h e usual way. Next followed digestion with I O cc. N X I O caustic potash, adding water as needed, oxidation with hydrogen peroxide a n d strong acidification with 2 5 cc. concentrated hydrochloric acid. T o remove chlorates4 a n d silica-which must necessarily be present from t h e action of alkali on glass-the solution was evaporated t o dryness a n d t h e residue was heated several hours at 105 t o 110'' C. It was t h e n t a k e n u p with hot water a n d 5 cc. concentrated hydrochloric acid, a n d t h e filtered solution, after cooling a n d diluting t o about 700 cc., was precipitated cold with a j per cent solution of barium chloride through a capillary t u b e according t o t h e procedure of Walter Allen a n d Bishop. T h e next d a y t h e precipitate was filtered on paper, cautiously ashed in a platinum crucible a n d ignited for 30 min. in t h e covered crucible over a No. 3 M6ker burner. T o determine t h e value of t h e factor S/BaS04 under these conditions, 2 j cc. of N / 2 sulfuric acid were precipitated after t h e addition of hydrochloric acid only, a n d after t h e addition of I O cc. of N X I O caustic potash, acidification, evaporation, etc., as in t h e method of analysis, a n d this factor was used in calculating t h e results. T h e trace of sulfur derived from t h e reagents was determined a n d allowed for in all t h e work. All operations were performed in duplicate. T h e samples were made after different formulas in connection with another investigation. T h e y were diluted a n d analyzed, using t h e gravimetric method for sulfide sulfur, I t o 3 days after preparation. For t h e determination of t h e poly-sulfur figure t h e dilutions unfortunately were not made until between 8 to I O weeks later, t h e concentrates being preserved meanwhile in well-filled a n d well-sealed bottles. It is not desired t o discuss a t t h e present time changes which may occur in lime-sulfur solutions during storage, b u t it is necessary to give here t h e results for thiosulfate sulfur also. 1 2 3
Bur. of Chem., Bull. 163, p. 70. J . Am. Chem. SOC.,82 (1910),588. Proc. 8th Intern. Congr. Appl. Chem., 1 (1912), p . 33. Compare Ramsay, J . Agr. Sci., 6 (1914), 194.
341
T h e results obtained appear in Table I, expressed as percentages of t h e diluted samples.
Sample A.. B..
... . ... . .. .. .,
C ......... D ..... . ...
E..,. . . . . .
TABLEI-RESULTS IN PERCENTAGES FIRSTDILUTION SECONDDILUTION Thiosul- Sulfide S Thiosul- Sulfide S fate S Gravimetric Sum fate S Volumetric Stim 0.387 1.622 2.009 0.378 1.644 2.022
0.458 0.453 0.418 0.444
1.674 1.755 1.801
1.790
2.132 2.208 2.219 2.234
0.445 0.443 0.408 0.440
1.744 1.815 1.839 1.819
2.189 2.258 2.247 2.259
The volumetric method for sulfide sulfur gave distinctly higher results in all cases, t h e actual differences varying from 0.022 per cent t o 0.070 per cent. B u t i t is evident t h a t t h e thiosulfate sulfur decreased slightly during storage in all cases. If it is permissible t o assume t h a t some thiosulfate sulfur h a d become changed t o sulfide sulfur, a n d comparison is made between t h e sums of the t w o forms of sulfur, t h e volumetric method still gives t h e higher results in all cases, t h e actual differences varying from 0.011per cent t o 0.057 per cent. The parallelism indicates a greater fault in t h e factors employed for calculating t h e results t h a n in t h e rationale of either method, a n d since t h e factor S / B a S 0 4 is purely empirical under t h e conditions of t h e gravimetric method t h e probability of error rests there. No experiments have been performed upon t h e applicability of t h e method t o use dipping baths contaminated with filth from animals. CONCLUSIONS
Methods are now available for estimating iodometrically t h e three important forms of sulfur in limesulfur solutions; thiosulfate sulfur, mono-sulfur a n d poly-sulfur, thiosulfate being t h e substance directly titrated in each case. The methods appear theoretically sound a n d practically applicable. The use of a single standard solution which can be so easily a n d accurately prepared a n d used as N / I Oiodine means a possibility of increased accuracy, as well as a saving of time, over t h e gravimetric estimation of sulfur as barium sulfate under conditions which demand t h e employment of a n empirical factor. BIOCHEMIC DIVISION,BUREAUOF ANIMALINDUSTRY, DEPARTMGNT OF AGRICULTURE, WASHINGTON
A NEW APPARATUS FOR THE DETERMINATION OF SOIL CARBONATES AND NEW METHODS FOR THE DETERMINATION OF SOIL ACIDITY' B y E. TRUOG Received October 29, 1915
I n recent years a number of methods a n d forms of a p p a r a t u s have been devised for t h e determination of soil carbonates and acidity. The present paper makes no a t t e m p t t o discuss in detail the methods a n d apparatus which have been devised a h d advocated. T h e apparatus here described is the result of a n a t t e m p t t o devise a form which embodies simplicity, ease of operation a n d accuracy of results. I n these respects it is believed t o have certain marked advantages. 1 Published with the permission of the Director of the Wisconsin Experiment Station. The writer is greatly indebted to G P. Wolf, T I,. O'Hora and A. H. Neumann for assistance in trying out the apparatus and methods.
