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ALVD E S G I S E E R I S G C H E M I S T R Y
ceedingly variable. I p all t h e samples from grain the amount of charlock was invariably greater t h a n t h a t of brown mustard, ranging from 9 j . 1 t o j 7 . 3 per cent as calculated t o t h e pure wild mustard after correcting for foreign seed and impurities. A single sample of wild mustard from flax seed was almost absolutely pure brown mustard. I t should further be noted t h a t t h e volatile oil obtained in the commercial samples was approximately proportional t o t h e percentage of brown mustard present. This relation is so uniform t h a t t h e volatile oil can be calculated from t h e botanical analysis with practically as great accuracy as b y direct determination. For this purpose, t h e following formula based on t h e determinations made on t h e samples of t h e seeds separated from commercial wild mustard may be used: T' = 2 . 4 2 B 0.Ij C in which 1- is t h e percentage of volatile oil, B is t h e percentage of brown mustard a n d C is t h e percentage of charlock. comparison of t h e percentages of volatile oil found b y analysis a n d as calculated b y this formula in the samples of commercial wild mustard seed cleaned free of foreign seeds is given in t h e last column of Table I. I t can hardly be expected t h a t a formula based on determinations made on only one sample each of brown mustard and charlock will give strictly accurate results in ail cases. b u t t h e figures obtained on t h e samples examined b y us s h o w remarkable agreement and suggest further work both on wild mustard seed a n d t h e cake. Determinations of volatile mustard oil in mustard flour may prove useful in estimating t h e approximate amount of charlock present as a n adulterant provided this determination is supplemented b y careful microscopic examination. It should not be forgotten, however, t h a t in t h e presence of white mustard, which, like charlock, yields practically no volatile oil, or of black mustard. which m a y contain more t h a n t h e brown, it would be impossible t o arrii-e a t a correct estimat.e from t h e volatile oil alone. Of special value in t h e case of such mixtures is a n estimate based on t h e amount of hulls reacting with acid chloral hydrate solution.
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B i - R E A UO F CHEMISTRY, WASHINGTOS, D. C
THE DETERMINATION OF SULFATES IN SOILS B y P. E. BROWNA N D E. H. KELLOGG Received February 15. 1915
I n undertaking a s t u d y of t h e process of sulfofication or sulfur oxidation in soils, t h e first problem which arose was t h e selection of a n accurate method for t h e determination of t h e sulfates. Tt'iley gives directions for t h e determination without comment as t o a n y difficulties t o be met with. As he describes it, t h e method merely calls for t r e a t m e n t of t h e soil with cold, dilute hydrochloric acid, filtration and precipitation with barium chloride a n d weighing t h e sulfate formed. I n the work of t h e few investigators who have made observations on t h e formation of sulfates in soils, t h e method of extraction of t h e sulfates is usually not mentioned a n d when t h e point is considered worthy of notice, t h e rather indefinite statement is made t h a t t h e soil
Vol. 7 , S o . 8
is treated with dilute hydrochloric acid. I s it important t h a t a certain strength of acid should be employed in order t o accomplish complete extraction? W h a t should be t h e length of time of cont a c t with t h e acid? These are questions which immediately arise and t h e experiments reported here were carried out t o answer t h e m a n d t o develop a method which would permit of a n accurate estimation of sulfates as such in the soil E X P E RI 31E S T A L
I n the first experiments, therefore. zoo-gram quantities of soil were shaken in the shaking machine for two hours with 2 0 0 cc. of 0 . j . 1.0, 2 . 0 , j . 0 and 10.0 per cent hydrochloric acid and with 2 0 0 cc. of water. -4 comparative series was run under exactly the same conditions except t h a t 2 cc. of a j per cent solution of magnesium sulfate were added t o each Ioo-gram q u a n t i t y of soil. T h e amount of sulfate extracted in each case from the soil itself \vas thus determined and subtracting this figure from t h e total amount of sulfate obtained, t h e extraction from t h e magnesium sulfate added was found. T h e sulfates were determined in these cases by t h e usual gravimetric method using barium chloride. T h e results of these tests appear in Table I . TABLE~--CO~;CESTRATIONS
OF
ACID VARIED
V
Milligrams sulfur Not extr. ncm ULI 6%s Ifilligrams S extracted as Added from Lab. *Su!iates SOa from a s hIgSO4 S O . i .$" ' Duplicates Av. MgSOa M g S O i added I , z.... 0.5 0.97 None 1.18 0.77 ... 3, 4.., . 0.5 24.19 26.04 25.11 0.1 2.1:i 4 2 6 : 6 3 2.49 1.10 1.76 5, 6.... 1.0 S o n e .... 1.43 7, s.... 1.0 0.1 23.94 26.38 25.16 23.i 3 26: 63 2.90 1.i4 0.91 1.32 9, 10 , . . 2.0 N'one . ,. 24.47 24.47 24.47 1 1 , 12 .... 2.0 0.1 zi: is 2 6 : 63 3.48 13, 14 . . . . 5 . 0 1.44 2.04 None .... 1.74 30.92 31.46 31.19 15, 16 . . . . 5.0 0 . 1 29:45 26:63 Excess 1.10 1,. 18 . . . . 10.0 S o n e 1.40 1.25 ... .... 36.52 45.38 40.95 19,20 . . . . 10 0 0.1 39:jO 26.63 Excess 4.00 4.12 21, 22 . . . . Water NTone 4.06 .... 23. 24 ..... Water 0.1 30.70 30.34 30.52 26:46 26: 63 0.1;
$t g,
Upon examination of these results it is found t h a t treating a soil with hydrochloric acid in any of the strengths used did not permit of t h e determination of sulfates known t o be contained in t h e soil. The weakest acid used allowed only a partial recovery of t h e sulfate added and as t h e concentration was increased u p t o 2 . 0 per cent acid the recovery became gradually smaller. With j and I O per cent acid, however, t h e recovery was entirely too high, t h a t with t h e I O per cent acid being greater t h a n t h a t with t h e j per cent. I t is evident from these tests t h a t there are some disturbing factors which prevent t h e extraction of sulfates from soils b y hydrochloric acid. Van Bemmelenl observed t h a t with hydrochloric acid much humus substance and iron oxide were dissolved and t h a t these interfered with t h e determination of sulfates, causing low results. H e found further t h a t it mas impossible to remove these substances without obtaining high results because of t h e oxidation of t h e sulfur in the dissolved organic matter. Furthermore, with j or I O per cent acid there is undoubtedly some solution of silica a n d this would make t h e results too high, a s t h e y have been shown t o be. I t m a y be concluded, therefore, from these results 1
L a n d v . V e r s . Sla., 37, -184.
Aug., 1915
T H E JO17RS.4 L OF I S D L - 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 dilute hydrochloric acid is quite unsatisfactory for t h e extraction of sulfates from t h e soil because of t h e ferric oxide a n d organic m a t t e r dissolved b y t h e acid a n d because increasing t h e concentration of t h e acid makes t h e results t o o high on account of t h e interference of silica. Examining t h e results where t h e soil was t r e a t e d with water. i t is found t h a t rather complete extraction of t h e sulfates present in t h e soil was secured. Almost four times as much was extracted from t h e soil itself as with a n y of t h e hydrochloric acid solutions a n d t h e magnesium sulfate added t o t h e soil was practically entirely recovered. F u r t h e r tests t o ascertain t h e efficiency of water for extracting sulfates were. therefore, planned. I n t h e first place it was deemed advisable t o determine whether t h e a m o u n t of sulfates extracted from soil with water could be increased by longer periods of shaking. T h e same soil used i n t h e preceding t e s t s was, therefore. shaken for 2, 4 , a n d 6 hours i n t h e shaking machine a n d t h e results secured, which a r e given in Table 11, show t h a t just as much sulfate was extracted in t w o hours as i n t h e longer periods TABLE11-EFFECT OF TIMEOF SHAKING o x EXTRACTIONS Lab. Hours Milligrams sulfur as SOa in soil No. shaken Duplicates Av. 1 , 2 ...................... 2 3.42 3.51 3.46 3 , 4. . . . . . . . . . . . . . . . . . . . . . 4 3.54 3.62 3.58 5 , 6 ...................... 6 3.04 3.64 3.34
,
It would seem, therefore, t h a t t h e conclusion might b e drawn t h a t complete extraction of sulfates may b e accomplished b y shaking with water for t w o hours. It was felt, however, t h a t in some cases quite considerable a m o u n t s of sulfates might be present in soils a n d i n t h e sulfofication tests which it was purposed t o carry o u t there was no d o u b t b u t t h a t it would be necessary t o encourage a rather large accumulation of sulfates t o permit of t h e securing of definite d a t a . Furthermore, magnesium sulfate, which was used in t h e previous series, is readily soluble, much more so t h a n sulfates, such as calcium sulfate, more likely t o be present in t h e soil. Consequently experiments were arranged t o determine t h e ability of water t o extract calcium sulfate from soils. I n t h e first tests, dehydrated gypsum was employed a n d t h e extraction with water was found t o be quite incomplete t h e discrepancies being rather large when t h e larger amounts of gypsum were used b u t still appreciable with t h e smaller amounts. Gradually increasing t h e time of shaking with mater permitted an increasing extraction of t h e sulfate, t h e largest proportion of t h a t added being obtained when t h e period of shaking was eight hours. Still, however, t h e recovery was incomplete. T h e same a m o u n t s of gypsum as were used mixed with t h e soil were shaken alone with water for varying lengths of time a n d t h e results showed t h a t while mixing with soil retarded quite considerably t h e r a t e a t which t h e sulfate went i n t o solution in t h e water, t h e extraction was incomplete in t h e absence of soil even where only very small a m o u n t s of t h e gypsum were used. T h e pure, dehydrated gypsum used in t h i s work has been found t o be very much more difficultly soluble t h a n t h e hydrated calcium sulfate a n d
68;
hence t h e tests were continued using chemically pure calcium sulfate containing t w o molecules of water. This compound is not only more readily soluble b u t i t is believed t o be more nearly like t h e compounds present in t h e soil t h a n t h e dehydrated gypsum. Tests of t h e solubility of t h e h y d r a t e d sulfate u n mixed with soil showed complete solution in t w o hours' shaking. Varying a m o u n t s of t h e material were t h e n added t o t h e soil a n d t h e mixture shaken for varying lengths of time with water. T h e results given in Table I11 show t h a t t h e extraction was complete in six hours. Other results using ground a n d unground soil showed t h a t while t h e extraction was somewhat quicker in t h e ground t h a n in t h e u n ground samples, shaking with water for 6-8 hours accomplished in all cases t h e complete extraction of t h e sulfate added. T h e a m o u n t s of sulfate added mere much greater t h a n would ordinarily occur in soils. a n d calcium sulfate is probably t h e most difficultly soluble of a n y sulfate which might occur in t h e soil. Hence t h e solution of t h i s material in t h e a m o u n t s tested m a y be regarded a s indicating t h a t sulfates in t h e soil m a y be estimated readily b y shaking with water for a period of six t o eight hours. TABLE111-EXTRACTIONSWITH WATER Milligrams S extracted MG. SULPCR N o t extr. -5" Hrs As sulfates From Added from Lab. $ $ S shaSO4 as sulfate NO. ken Duplicates Av added SO4 added 1, 2 . . . . . . . 0.25 4 5 0 . 0 0 5 0 . 0 0 5 0 . 0 0 4 6 . 0 0 46.50 0 . 5 0 3 , 4 . . . . . . . 0.25 6 5 0 . i 2 5 0 . 4 6 5 0 . 5 9 46.59 4 6 . 5 0 . . . 5, 6 . . . . . . . 0 . 2 5 8 50.38 5 0 . 1 2 50.25 46.25 46.50 0.25 7, 8 . . . . . . . 0.05 6 13.36 13.12 13.24 9.24 9 . 3 0 0.06 9. IO . . . . . . . N-one 8 4.00 4.00 4.00 . . . . . . . . . .
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One point further was tested in this work a n d t h a t was t h e use of t h e sulfur photometer. Gravimetric determinations of sulfates are very tedious a n d i t was almost essential t h a t a more expeditious method be employed j f large numbers of determinations were t o be made such as are necessary in studies of sulfofication. T h e photometric method was tested a n d compared with t h e gravimetric a n d it was found t o be quite as accurate a n d much quicker. I t s use for t h e determination of sulfates i n soils should be strongly advised.
c 0s c L L- SI0 N s I-Sulfates cannot be extracted from soils b y t r e a t ment n-ith dilute hydrochloric acid because of t h e interference of organic substances a n d iron compounds. 11-Shaking soil with twice its weight of water in t h e shaking machine for six t o eight hours extracts sulfates completely. 111-The sulfur photometer is a rapid a n d accurate means of determining sulfates. '
LABORATORY OF S O I L CHEMISTRY A X D BACTERIOLOGY IOWA S T A T E COLLEGE, 4 M E S ~
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COMPOSITION OF THE SALINES OF THE UNITED STATES. IV-A CORRECTION By J. W. TURRBNTINE~ Received January 28, 1915
Occasion having arisen for recalculating t o t h e conventional combination t h e results i n t h e analysis, in I Scientist in Soil Laboratory Investigations. Bureau of Soils, U . Dept. Agriculture.
S.
