The Determination of Minute Amounts of Sulfur Dioxide in Air

Ind. Eng. Chem. , 1914, 6 (4), pp 298–301 ... Publication Date: April 1914 .... Chemical Society, CAS, and ACS Publications in Liverpool from August...
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difficulty in providing for t h e extraction of t h e rich wood with caustic soda alone. T h e pulp obtained from long-leaf pine is characterized b y unusual length of fiber, t h e length being 4-6 millimeters, or a b o u t twice t h a t of spruce fiber. This quality, coupled with t h e favorable strength a n d flexibility of t h e fiber, imparts t o t h e finished paper unusual toughness a n d resistance t o folding a n d bursting. I t is well suited for making high-grade wrapping paper, board stock, etc. With further s t u d y of t h e methods for cooking, beating a n d bleaching, i t is expected t h a i t h e uses of t h e pulp will be greatly extended. SIGNIFICAKCE


T h e d a t a obtained i n these investigations are not necessarily representative of those which would hold in industrial practice, nevertheless t h e results of t h e investigation clearly indicates t h e feasibility of a simple two-stage alkaline t r e a t m e n t for southern pine b y which i t is possible t o obtain a high recovery of valuable products from t h e primary constituents of t h e wood. T h e crude products are isolated in a favorable s t a t e of purity a n d require little subsequent refining. T h e process is characterized b y simplicity in manipulation a n d in separation of e n d products. Moreover, t h e materials used in t h e reduction, as well as t h e ultimate products themselves, are few in number a n d simple in nature. There is no waste of alkali at a n y point. T h e portion with'drawn from t h e cycle in t h e form of precipitated sodium resinate serves t o enhance t h e value of t h e rosin fraction. Incineration of t h e waste pulping liquor provides for t h e recovery of t h e balance of t h e alkali, within t h e practical limits of mechanical efficiency. As mentioned before, practical application of this t r e a t m e n t of t h e more resinous materials could be carried o u t most conveniently as supplementary t o ordinary pulp-mill operation on lean wood. Only slight modifications i n certain of t h e existing digester units would be necessary t o t a k e care of t h e richer grades of pine. T h e supply of f a t wood could be obtained b y sorting t h e raw material received at t h e pulp mill or b y procuring lightwood, etc., from independent sources. There is also a possibility t h a t t h e first stage of t h e process, namely, t h a t of extraction with caustic soda or sodium carbonate, could be employed in treating those grades of resinous waste which would not lend themselves t o final pulping. Charred or unsound wood might be steamed with dilute alkali for t h e recovery of rosin a n d turpentine, without provision for t r e a t m e n t of t h e extracted chips. T h e economic merits of such a scheme could be decided only b y actual trial. CHEMICALENGINEERING LABORATORY COLUXBIAUNIVERSITY,NEW Y G R K





I n t h e case of most of t h e determinations of small amounts Of dioxide in air, which have so f a r Presented at the Rochester Meeting of t h e American Chemical Society, Sept. 9, 1913.

Vol. 6, No. 4

been made, considerable volumes of sample were available. Methods based upon t h e aspiration of a large a m o u n t of air through a small q u a n t i t y of liquid, a n d t h e gravimetric estimation of t h e retained sulfur could therefore be used. I n such cases t h e results showed t h e average sulfur dioxide content for various periods of time. T h e problem a t present in h a n d w a s t h e estimation of sulfur dioxide at a n y particular i n s t a n t in t h e air of railway tunnels.' T h e approximate dilutions which were t o be determined were ascertained b y liberating given a m o u n t s of t h e gas i n a closed room a n d noting t h e odor. I t was f o u n d in this way t h a t I O p a r t s per million produced a n effect similar t o t h a t often experienced 'while passing through a smoke-filled railway tunnel. I n order t o collect what might be termed instantaneous samples. use was made of evacuated 2 . j liter bottles. These were provided with seals made of short glass tubes passing through t h e stoppers. On breaking t h e tip of t h e t u b e , t h e air entered within a few seconds, a n d therefore constituted a fairly representative sample of t h e atmosphere a t t h e particular point a t which t h e seal was broken. I t therefore became necessary t o determine in 2 . 5 liter samples of air, amounts of sulfur dioxide varying from a b o u t 0 . 0 0 2 5 t o 0 . o j of a cubic centimeter. T h e determination of fairly large amounts of sulfur dioxide b y iodometric titration can, of course, be made with considerable accuracy. T h e application of t h i s method t o the determination of very small a m o u n t s of t h e gas appeared t o be simply n question of ascertaining t h e peculiarities of t h e iodine reaction a t great dilution, a n d selecting those conditions most favorable t o constancy a n d accuracy of results. Experiments were made with dilutions of sulfur dioxide of t h e order of magnitude under consideration, namely, one to t w e n t y parts per million. T h e titrations were made in t h e 2 . j liter white glass bottles, using N / ~ o o o iodine a n d thiosulfate solutions. I n those cases in which a n excess of iodine was used a n d t h e end point approached with thiosulfate, great difficulty was experienced in judging when t h e last trace of t h e blue color of t h e starch disappeared. It was also found t h a t even in t h e absence of sulfur dioxide, direct titrations with iodine a n d thiosulfate solutions gave quite different results, depending upon whether t h e e n d point was approached from t h e side of appearance or of disappearance of t h e blue color of t h e starch indicator. This point showed t h a t no method of determination of very small a m o u n t s of sulfur dioxide involving a back titration would be practicable. T h e results of t h e extended series of experiments showed t h a t satisfactory determinations can best be made b y adding j cc. of 0.1 per cent aqueous starch paste t o t h e bottle containing- t h e sample, a n d after rotating in such a manner t h a t t h e interior walls are entirely moistened, titrating with N / ~ o o o iodine solution t o appearance of t h e blue color of t h e starch iodide. T h e end point obtained in this manner is quite sharp, one or tm,o drops of t h e iodine being 1 A detailed account of t h e analytical results obtained h v the method here described will be given in a bulletin of the Hygienic Laboratory, U. S Public H e a l t h Service.

T H E J O U R N A L OF I N D I ' 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

Apr., 1914

sufficient t o produce t h e final distinct blue color. Blank titrations made i n exactly t h e same manner in a bottle containing air free from sulfur dioxide, required a n average of 0.3 cc. N / ~ o o oiodine t o yield a n equivalent color change in t h e aqueous starch solution. This correction must therefore be applied t o t h e titrations made upon samples containing sulfur dioxide. Since t h e reaction between iodine a n d sulfur dioxide is represented b y t h e equation 1 2 SO2 2 H z 0 = 2HI H2SO4 a n d I liter of SO? a t o o a n d 7 6 0 mm. pressure weighs 2 . 8 6 2 grams t h e n I cc. N / r o o o iodine should correspond t o 0 . 0 0 0 0 3 2 g r a m or 0 . 0 1 1 2 cc. SO2 (at o o a n d 7 6 0 m m . ) . I n order t o test t h e reaction at great dilutions t h e titrations of given mixtures of air a n d sulfur dioxide as shown in Table I were made.








Composition of mixture

Cc. Air 3875 250 3875 250 3875 250 3875 250 3875 250 3875 250 3875 250 2500 2500 2590 2500 2500 2500 2500 2500 2500 2500 2500 2500 2500 2500

c c . SO2 IOo and 760 mm.) 1.8 I .8 0.9 0.9 0.9 0.9 0.36 0,36 0.36 0.36 0 09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.018 0.018 0.018 0.018 0.018 0.009 0.009

Per cent of Cc. standard Calc. vol. SO2 actual SOz iodine (cor.) (0' a n d 760 mm.) found

13.35 N/100 13.5 6.55 " 6.8 6.75 '' 6.7 2.65 " 2.85 " 2.75 2.75 IC 6 . 9 5 A7/1000 7.25 6.85 7.0 " 6.5 " i.5 " 6.9 '' 7.1 " 7.5 " i.25 " 6.55 " 1.15 1.05 " 1.15 " 1.1 " 1.1 0.8 0.6 " 'I

' j


' I


1.49 1.51 0.73 0.i6

0.76 0.75 0.30 0.32 0.31 0.31 0,078

0.081 0.077 0.078 0.076 0.084

O.Oi7 0.080 0.084 0.081 0,073 0.013 0.012 0.013 0.012 0.012 0.009 0.00i

83 84 81 84 84 83 83 59 86 86 87 90 86 87 81 93 86 85 93 90 81 72 66 72 68 68 98 75

T h e sulfur dioxide was measured b y successively diluting a given volume of the pure gas with air a n d transferring definite amounts of t h e mixture t o partially evacuated bottles of t h e capacity indicated in t h e table under "Cc. Air." An examination of this table shows t h a t in all cases lorn results are obtained. T h e average for concentrations of SO2 between 0 . 0 9 a n d 1.8 cc. is 86 per cent a n d for concentrations below 0.09 (except Det. No. 2 7 ) i t is 7 0 per cent. There are two possible explanations for t h e low results. Either t h e reaction of t h e iodine with t h e sulfur dioxide m a y be incomplete a t this dilution or else partial oxidation of t h e sulfur dioxide occurs when i t is diluted with air. Some evidence upon t h e latter of these assumptions is contained in t h e table. T h u s i t will be seen t h a t in practically all of t h e duplicate titrations made i n large a n d in small bottles, slightly lower results are obtained i n t h e larger bottles, t h a t is, in t h e more highly diluted mixtures.


Also t h e percentage of sulfur dioxide recovered is lowest in t h e case of t h e more dilute mixtures. It m a y therefore be concluded t h a t some oxidation takes place simply upon allowing sulfur dioxide t o diffuse in a large volume of air of ordinary dryness. I n regard t o t h e incompleteness of t h e reaction, i t was pointed o u t by Volhard' many years ago t h a t in titrating aqueous sulfurous acid solution with standard N / I O iodine, less sulfur dioxide is found when t h e titration is made with t h e iodine, t h a t is, t o appearance of t h e blue starch color, t h a n when made in t h e reverse direction. At I/ I O normal concentrations the difference amounted t o about j per cent of t h e sulfur dioxide present. Results for more concentrated solutions are given, b u t none for solutions more dilute t h a n 1 / 1 0 normal. In order t o obtain d a t a upon this point a n experiment was made by us as follows: X standard solution of sulfur dioxide was prepared by dissolving a n accurately measured volume of t h e gas in distilled water a n d diluting t o a known volume. The first dilution contained 1.097 grams SO2 per 1000 cc. T h e second dilution contained 0.1097 gram S O z per 1000cc. a. Titrations made with t h e first dilution a n d T / I O iodine : 1 0 . 3 8 cc. N/10 iodine required 35.05 cc. S O , solution = 98.6 per cent SO2 found. 35 05 cc. SO2 solution required 9.96 cc. S / l O iodine = 83.0 per cent SOz found.

b. Titrations made with second dilution of solution a n d iV/ I O O iodine :


10.1 cc. N,'100 iodine required 32.3 cc. SO2 solution = 91.5 per cent SOz found. 32.3 cc. SOz solutio2 required 9.54 cc. S / l O 0 iodine = 86.2 per cent Son found.

c. Titrations made with second dilution of solution a n d N / ~ o o oiodine:


5 0 0 cc. K/lOOO iodine required 15.75 cc SO2 solution = 92.5 per cent SOz found. 15.0 cc. SO2 solution required 43.6 cc. A'/lOOO iodine = 83.7 per cent SOz found.

Although these results are not perfectly consistent, they show t h a t t h e titration t o appearance of t h e blue color of t h e starch indicator gives t h e lower results, a n d t h e actual percentage recovered is approximately equal t o t h a t found by titrating t h e sulfur dioxide a n d air mixtures i n t h e large 2 5 0 0 cc. white glass bottles, as reported in Table I. A more detailed s t u d y of this incomplete recovery of sulfur dioxide b y iodine titration would be of considerable interest, b u t further experiments m-ere not made b y us, since i t was evident t h a t for t h e purpose of t h e present investigation of tunnel air, greater accuracy was not required. F r o m a consideration of t h e above experiments i t is evident t h a t a correction factor for incompleteness of t h e reaction a t t h e great dilutions must be applied t o t h e iodine titrations. T h e selection of this factor was based upon the results shown in Table I. Here i t is seen t h a t for concentrations between about 4 a n d 40 parts per million t h e recovered sulfur dioxide lies between 7 0 a n d 86 per cent. It was therefore con1

J. Volhard, Liebig's Annalen, 242 (1887), 93.


3 00

cluded t h a t t h e factor 1.3 would bring t h e results sufficiently near IOO per cent for all practical purposes. There is one other point which must be taken into consideration in connection with t h e determination of small a m o u n t s of sulfur dioxide, a n d t h a t is t h e r a t e of loss due t o oxidation, on standing. It mas early noticed t h a t t h e presence of moisture hastens this loss very materially. E v e n in t h e case of bottles dried as carefully as possible a n d with t h e exercise of reasonable precautions t o exclude moisture, i t was found t h a t t h e sulfur dioxide began t o disappear within a short time. Some experiments were therefore made for the purpose of ascertaining how soon t h e titrations of given samples m u s t be made in order t h a t loss due t o oxidation m a y be avoided. A series of experiments was first made with carefully dried bottles. T h e results are shown in Table 11. TABLE11-SHOWINGRATE OF DISAPPEARANCE OF SVLFUR DIOXIDEFROM D R Y 2500 C c . BOTTLES Found vol. .V:lOOO SO? ( a t O o iodine (cor.) and 760) Per cent SO? cc. cc. recovered 0.094 104 6.45 0.098 109 6.75 0.052 60 3.6 0.092 100 6.3 5.15 0.075 83 0,065 72 4.5 0.042 4i 2.85 0 . 0 4 5 100 3.1 0.037 82 2.55 1.6 0,023 52 0.95 0.014 31 0 . 0 1 9 43 1.35 1.25 0.018 40 0.022 50 1.55 0 . 0 2 2 50 1.55

DILUTEMIXTURES WITH AIR Volume of contained S o t (at O o a n d 760)

0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.045 0.045 0.045 0.045 0.045 0.045 0.045 0.045

Time of standing Minutes 10.0 20.0 65.0 90.0 135.0 160.0 225 .o 0.5 14.0 30.0 45.0 60.0 75.0 100.0 130.0


I n t h e case of t h e d r y bottles i t would appear from t h e results t h a t t h e disappearance is the more rapid, t h e more dilute t h e sulfur dioxide. This, however, cannot be definitely concluded since t h e experiments with t h e moist bottles indicate t h a t t h e moisture , f a c t o r plays a much more i m p o r t a n t p a r t t h a n t h e concentration. T h e difference i n r a t e of loss as shown b y t h e first series of seven determinations a n d t h e second series of eight determinations in Table 11, m a y , i n fact, be due t o inappreciable differences in moisture content of t h e laboratory air with which t h e dilutions were made i n t h e t w o cases, rather t h a n t o t h e jo per cent difference in concentration of t h e sulfur dioxide itself. I n t h e experiments with moist bottles t h e irregularities were so great t h a t n o conclusion in regard t o t h e r a t e of oxidation of t h e sulfur dioxide could be drawn. I n some cases a b o u t half of t h e added gas h a d disappeared within a few minutes, a n d in others a loss of only a b o u t 3 0 per cent h a d occurred in half a n hour. I n practically all cases only a small fraction of t h e used sulfur dioxide was recovered after one hour. Th-ese irregularities were found even in spite of special efforts t o maintain uniform conditions for t h e experiments. T h e results demonstrated t h e necessity of using d r y bottles for collecting t h e samples. T h e y also indicate t h a t except on very d r y days i t is necess a r y t o make t h e titration mithin less t h a n half a n hour after collecting t h e samples in order t o avoid low re-

1'01. 6, NO. 4

sults due t o gradual oxidation of t h e sulfur dioxide. In order t o test further t h e direct iodine titration method for sulfur dioxide, several series of determinations were made upon samples of air from a r o o m in which given volumes of pure sulfur dioxide were liberated. T h e room was CJ f t . X I O it. X 1 3 f t . = 1 1 7 0 cubic feet capacity a n d contained a rather large window a n d door. T h e walls were of painted plaster. N o a t t e m p t t o seal the cracks around t h e window a n d door was made. X large electric f a n was a r ranged t o cause a rapid circulation of t h e air in t h e room. For each experiment t h e given volume of sulfur dioxide w a s liberated quickly a n d after a 2 to 6 minute period of stirring with t h e f a n , t h e seals on t h e first series of eight evacuated d r y bottles placed near together on a table, were broken practically simultaneously. A second series of six samples were t a k e n after a n additional j t o I O minutes' stirring. These samples were t i t r a t e d as quickly as possible in all cases. T h e analytical results are given below in t h e order i n which t h e titrations were made: Experzment I-I-olume of 302 liberated = 500 cc. or, on the basis of the volume of the room, 15 parts SO? per I,OOO,OOO. First series of samples taken after 2 minutes' stirring, contained, respectively: 5.0, 7.9, 6.4, 4 . 1 , 1.9, 5.5, 0.9, 5.5 parts SO2 per I,OOO,OOO. Second series of samples taken after 6 minutes' stirring contained, respectively : 7 . 6 , 6.0, 5 ..j,6.7, 4. I , 5.5 parts SOZ per I,OOO,OOO. E x p e r i m e n t TI-Volume of SOZ liberated = 500 cc. or 15.0. parts per I,OOO,OOO. First series of samples taken after 5 minutes' stirring contaired, respectively: 10.0, 9.9. 7 . 0 , 5.0, 9.6, 1.2, 6.1, 5.8 parts , 5 0 2 per I,OOO,OOO. Second series of samples taken after I O minutes' stirring contained, respectively: 6.1, 6.1, 5.8, 4.1, 4.7, 5.8 parts SO? per I,OOO,OOO. E x p e r i m e n t III-Volume of SOZ liberated = 500 cc. or 15.0. parts SO2 per I,OOO,OOO. There were also liberated 3300 cc. of COZ ( = IOO parts per I,OOO,OOO) generated by mixing aqueous NazC03 and HzSOd solutions. The weather outside was cloudy and moist. First series of samples taken after 5 minutes contained, respectively: 3.5, 2.3, 1.8, 6.4, 3.2, 2.6, 1.2, 1 . 2 parts , 5 0 2 per I,OOO,OOO. Second series of samples taken after I O minutes contained, respectively: 4.6, 7.0, 2 . 3 , 1.8, 3.8, 3.2 parts SOZper I,OOO,OOO. E x p e r i m e n t IV-Volume of SO? liberated = 213 cc. or 6.4 parts per I,OOO,OOO. First series of samples taken after 3 minutes contained, respectively: 5.2, 2 . 3 , 1.2, 1 . 2 parts SO2 per I,OOO,OOO. Second series of samples taken after 6 minutes contained, respectively: 3.2, 2.3 parts SO?per I,OOO,OOO.

I t will be noted t h a t in all cases considerably less. sulfur dioxide was recovered t h a n liberated. There appears t o be a n initial loss amounting t o about 3 0 . t o j o per cent of t h e liberated gas. T h e variation between t h e individual samples of t h e second series. in each case is less t h a n for t h e first series, d u e probably t o t h e more thorough mixing after the longer period of stirring. T h e variations between t h e several. experiments are very significant. T h u s in Experiment. 111, made on a cloudy, d a m p d a y a n d in which considerable water vapor was set free during t h e genera-tion of t h e carbon dioxide, t h e recovered sulfur dioxide is appreciably lower t h a n in t h e case of Experiments I a n d 11. T h e moisture content of t h e air, therefore,. influences t h e loss of sulfur dioxide set free in t h e room. t o a very considerable extent.



.5pr., 1914



It has been shown t h a t very minute amounts of liter samples of air can be desulfur dioxide in 2 l termined b y direct titration with SI 1000 iodine. A correction factor of 1.3 for t h e apparent incompleteness of t h e reaction at t h e great dilution must be applied. On account of t h e gradual oxidation of t h e sulfur dioxide, t h e titrations must be made within a short time after t h e collection of t h e sample. The presence of moisture hast& t h e loss b y oxidation \-cry materially-.


KO. County 1




Received January 7 , 1914

ISTRoDcCTIOS-ST’hen, in July, 191 I , Professor IT. H. K a r r e n ’ s article “Sugar Sand from I l a p l e S a p ; X Source of 1Ialic Xcid.”l appeared. N r . Lochhead h a d been engaged for some weeks in analyzing sugar sand a n d attempting t o prepare malic acid from i t . I n carrying out my suggestion t o treat t h e sand with dilute nitric acid, precipitate t h e malic acid as lead malate a n d liberate it b y treatment with hydrogen sulfide, he h a d found t h a t calcium bimalate could be crystallized out from t h e nitric acid solution, a n d transformed into free acid b y treatment with oxalic acid-essentially t h e process recommended by Warren. A h . Lochhead’s work was presented t o t h e Faculty of McGill University in 1912 as a thesis for t h e degree of M.Sc., b u t has not appeared i n print. T h e present article prepared during Mr. Lochhead’s absence is based upon his results. [ J . F. SNELL] P R E V I O U S L Y P U B L I S H E D Ah-ALYSES O F S U G A R S A N D

When t h e sap of t h e sugar maple has been concentrated t o a t h i n syrup b y boiling, a precipitate is deposited, which is known t o t h e sugarmaker as “sugar . s a n d ” or “niter.” T w o analyses of this precipitate,2 published previous t o Warren’s paper, indicated a content of 33.7 j a n d 40.10 per cent of calcium malate, respectively. These analyses included about 40 per cent of sugars a n d obviously referred t o t h e crude unwashed materials. Warren3 made a more detailed analysis of a single sample of washed sugar s a n d , which showed a calcium malate content of 68.64 per cent a n d a silica content of 7.74 per cent. ’


We have analyzed six washed samples, all of Quebec origin, five being t h e product of single sugar bushes, t h e other ( S o . 5 ) a mixture. T h e sources of t h e samples a n d t h e descriptions of t h e unwashed material are given in Table I . T h e samples were washed b y mixing thoroughly \$-ith hot water a n d filtering with a Buchner filter, t h e p;ocess being repeated until t h e sweet taste disappeared. I n most instances four 11Varren. Jour. A n e r . C h e m . Soc., 33 (19111, 1205. 2 Bryan, U. S . Dept. Agriculture. Bureau of Chemistry, Bull. 154 (1910), 55. One of t h e analyses is original, t h e other is quoted f r o m I n diana 4 g r . Expt. Station, 12th Annual Report, 1899, p . 74. T h e latter is also quoted a n d commented upon b y Sy. Jonr. Franklin I n s f . , 1908. 3 Loc. c i l .



High land, shallow, gravelly soil, limestone bottom High gravelly soil High land, slate and loam

Light brown

2 ‘Shefford 3 Shefford

Light brown Darker t h a n I or 2





Dark brown containing much syrup Light colored




THE ANALYSIS OF MAPLE PRODUCTS, IV The Composition of Maple Sugar Sand


Mixture from different parts of Shefford Co

1-ery dark, containing so much syrup a s t o make i t somewhat fluid

washings were sufficient. T h e 11-ashings invariably contained calcium as well as sugar. They readily underwent fermentation, liberating carbon dioxide a n d becoming acid in reaction. The mashed sugar sand was almost white and was non-hygroscopic, It h a d a specific gravity varying from 1.76 to 1.83 a n d averaging 1.80. T h e loss of d r y m a t t e r during mashing was determined in Samples I and j . I n four experiments TABLE 11-RESELTS OF



1 2 HzO . . . . . . , , . . . . 0.21 0.69 CaO . . . . . . . . . . . . 2 5 . 7 4 2 2 . 6 3 MnO.. . . .. . . . . . 1.87 1.38 MgO. . . . , , . . , . ... ... C;HaOd(a) . . . . . . . 5 3 . 7 3 4 6 . 4 9 6 . 1 6 18.55 SiOz . . . . . . . . . . . . ,...., ,.., 0.99


Total... . . . . . .



3 4 0.69 0.57 24.27 2 4 . 0 7 1.80 1.63 0.27 0.84 4 7 . 1 4 44.32 1 3 . 7 4 15.03 0.70 0.82





5 0.17 25.33 1.49 0.45 50.73 10.65 0.33

0.88 44.88 13.82 0.29



6 0.11 23.06












Ca . . . . . . . . . . . . . 17.76 C I H I O J ( ~. ,) . . . . . 61.17 Ratio 1: , . . . . . . . 3.44 CaCiHaOj, calculated: ( 1 ) f r o m C a. . . 76.22 (2) fromCiHeOs 79.67

15.62 52.90 3.38

16.75 53.64 3.20

16.61 50.44 3.04

17.44 57.73 3.31

15.91 51.06 3.21

Average 16.68 54.49 3.26

67.03 68.91

71.88 69.87

71.28 65.73

T4.83 75.25

68.28 66.56

71.59 70.98

( a ) Malic acid anhydride.

( b ) Malate radical.

on No. I i t varied from j I t o j j per cent a n d averaged j 2 . 7 per cent. I n four experiments on No. j i t varied from 49.5 t o j 3 a n d averaged j z . 1 per cent. METHODS O F ANALYSIS

M o i s t u r e was determined b y drying IO grams a t 100’. T h e milteral constitueizts were determined in t h e air-dry ash a n d calculated over t o percentage of t h e original material. A trace of iron was found i n all t h e samples. M a l i c a c i d was determined by a method similar t o a n d suggested b y t h a t of Warren, whose work h a d been published before our malic acid determinations were undertaken: I g r a m sugar sand a n d 2 j cc. normal oxalic acid were heated on t h e water b a t h for a n hour a n d a half. T h e product was filtered a n d washed, a n d t h e filtrate made u p t o z j o cc. Total acidity was determined in one 5 0 cc. aliquot. I n another, t h e residual oxalic acid w a s determined b y neutralizing with ammonia, acidifying with acetic acid, precipitating with calcium chloride, dissolving the washed precipitate in sulfuric acid a n d titrating with standard permanganate. T h e difference between total acid a n d residual oxalic acid represents t h e liberated malic acid.