Aug., 1915
T H E JO17RS.4 L OF I S D L - S T R I A L A N D ENGINEERING 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 matter 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 too high on account of t h e interference of silica. Examining t h e results where t h e soil was treated 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. Further 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 amount of sulfates extracted from soil with water could be increased by longer periods of shaking. T h e same soil used in t h e preceding tests was, therefore. shaken for 2, 4 , a n d 6 hours in t h e shaking machine a n d t h e results secured, which are given in Table 11, show t h a t just as much sulfate was extracted in t w o hours as in the 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 be drawn t h a t complete extraction of sulfates may be accomplished b y shaking with water for two hours. It was felt, however, t h a t in some cases quite considerable amounts of sulfates might be present in soils a n d in t h e sulfofication tests which it was purposed t o carry o u t there was no doubt 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. The same amounts 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 rate a t which t h e sulfate went into solution in t h e water, t h e extraction was incomplete in t h e absence of soil even where only very small amounts of t h e gypsum were used. T h e pure, dehydrated gypsum used in this 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 hydrated sulfate unmixed with soil showed complete solution in two hours' shaking. Varying amounts of t h e material were then added t o t h e soil a n d t h e mixture shaken for varying lengths of time with water. The 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 amounts 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 any sulfate which might occur in t h e soil. Hence t h e solution of this material in t h e amounts tested may be regarded as indicating t h a t sulfates in t h e soil may be estimated readily by 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 6 5 0 . i 2 5 0 . 4 6 5 0 . 5 9 46.59 4 6 . 5 0 . . . 3 , 4 . . . . . . . 0.25 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 and 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. The 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 the determination of sulfates in soils should be strongly advised.
c 0s c L L- SI0 N s I-Sulfates cannot be extracted from soils by treatment n-ith dilute hydrochloric acid because of t h e interference of organic substances and 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 and 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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~
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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 in t h e analysis, in I Scientist in Soil Laboratory Investigations. Bureau of Soils, U . Dept. Agriculture.
S.
T H E J O U R N A L O F I ' V D U S T R I A L A-VD E ~ V G I ~ V E E R I ~ VCGH E M I S T R Y
688
T'o~.7 , KO.8
CORRECTIONS
J I. E C .
Bulletin so. 94 Pp. h-o
4 Pp.
B S h-o
Original analyses made by R.
F. Gardiner except where otherwise noted CONVENTIONAL COMBINATIONS
IOIS 7 -
h-a
C1
NaCl
CaClz
MgClz
Sad304
Cas04
MgBrl
MgSO4
(a) A . R . Merz analyst. ( b ) K onlv b y Merz. ( c ) J. A. Cullen. analyst. ( d ) From s p r i n i north of Woodward. K'oodward C o . , Okla. Collected by P. L. Clifton, 1910. ( e ) D a t a incongruous: withdrawn. ( f l Same as Bull. 94, p. 5 4 , p i o . 1 7 and THISJ O U R N A L , 4, 8 3 2 , h-0. 26. (g) Values represent parts per 1000, not per cent.
this laboratory, of certain .Imerican salines.' numerous inaccuracies, inconsistencies a n d typographical errors have been discovered which it is our desire t o correct.
s.
Bull. 94, L-. Dept. of Agriculture, "The Occurrence of Potassium Salts in t h e Salines of t h e U S." Extended abstracts. THISJ O U R N A L , 4 (1912). 828 a n d 8 8 5 ; 6 ( 1 9 1 3 ) . 19.
T h e analyses have been recalculated by LIr. -2.R . XIerz, with t h e collaboration of Jlessrs. Gardiner and Cullen who have, in each case, inspected t h e or approved them IT7ithout inspection. ~h~ serious of t h e errors encountered are set forth in t h e
*
Aug.9
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
1915
table on page 688. Only t h e corrected figures a n d legends are recorded: reference is made t o both publications, t h e first number being t h a t assigned in Bulletin 94, a n d t h e second, t h e Bureau of Soils number assigned in articles which appeared in THIS JOURNAL.^ T o report in t h e conventional manner t h e results obtained i n t h e examination of t h e various brines submitted for analysis was a concession t o t h e supposed wishes of t h e laymen interested t o whom t h e statement of results as ions conveys b u t slight information. This concession was made against our best judgment, since t o report t h e various basic a n d acid radicles as combined is t o abandon for t h e moment t h e best conception of t h e state of salts in solution. T o calculate such analytical d a t a t o t h e saline combination is t o juggle figures. As t h e basis for t h e conventional combination t h e respective solubilities of t h e component salts, which anciently were regarded as entities, have been taken. This, likewise, is a false basis, since t h e I LOC.
cit.
689
solubility of each salt when alone in solution is different from i t s solubility when in solution with t h e other salts. T h e latter solubility is determined b y t h e equilibrium conditions obtaining for each system studied. T h e conventional combinations should represent, if anything a t all, t h e solids precipitated on evaporation from t h e system studied, a n d should be recorded i n the order of their precipitation. This could be determined only b y a n examination of t h e system under consideration. T h e value of t h e results previously published is scarcely diminished b y t h e errors introduced in t h e calculations previously published. However, t h e fact t h a t t h e system of calculation from ionic t o saline form is based on erroneous conceptions a n d therefore itself is erroneous does not excuse avoidable errors in t h e application of t h e system. For t h a t reason i t is desired t o substitute t h e recalculations herewith presented. BUREAUO F S O I L S . U. s. DEPARTMEXT OF AGRICULTURE WASHINGTON
LABORATORY AND PLANT A MODIFIED BURETTE CALIBRATING PIPETTE AND CERTAIN POINTS IN THE USE OF SUCH INSTRUMENTS By C. W. FOULK Received March 23, 1915
Some months before this article was prepared for publication, t h e writer was told b y t h e “Trouble Man” of a large chemical firm t h a t t h e laboratory a n d factory control difficulties he was called upon t o adjust were frequently caused b y inaccuracies in t h e volumetric ware employed, a n d he added t h a t in his opinion many young chemists a n d not a few old ones were unaware of this source of error. T h e “Trouble Man” must t a k e t h e responsibility for his statement about chemists, b u t t h e author is willing t o testify regarding t h e general depravity of uncertified volumetric ware. During t h e last t e n years t h e calibration tables of several hundred burettes have been examined a n d errors of 0.1 cc. or more have been found t h e rule rather t h a n t h e exception. Occasionally t h e corrections reach a truly surprising value. For example, a t least three otherwise innocent looking burettes have been found with errors of over 0.4 cc. in t h e first 2 0 cc. of t h e scale. It, therefore, cannot be too strongly emphasized t h a t all such measuring instruments must be calibrated before using. If only one or t w o burettes are t o be examined t h e method of weighing t h e water delivered from successive intervals is t h e simplest since i t involves no special apparatus. If, however, a larger number are t o be calibrated or if from time t o time a few must be tested, some form of calibrating pipette will be found a n advantage on account of t h e time saved a n d t h e simplicity a n d directness of t h e procedure. Several such pipettes have been described2 b u t in every case ’
1 Pipettes of the design described in this article and piovided with a ’ 0.01 cc. division scale on the upper stem can be secured from the KauffmanLattimer Co.,Columbus, 0. 2 Arndt, Cenlralblaf, 1856, p. 865; Scheiblei, J . pvakt. Chem., 7 6 ( 3 8 5 9 ) , 177; Ostwald, Ibid., N. F., 25 (1882), 452; Morse and Blalock, A m . Chem. J . , 26 (1894). 479.
a n important point has curiously enough been overlooked, namely, t h e use of t h e two-way glass cock as a n automatic zero adjustment. A modification employing this time-saving scheme will be described in this paper a n d in addition t h e general principles a n d procedures involved in t h e use a n d calibration of these calibrating pipettes will be given. It so happens t h a t in previous articles there is not very good agreement as t o t h e details of determining t h e capacity of t h e pipette itself a n d in some cases t h e methods of calculating t h e final values obtained for t h e different points on t h e burette scale are unnecessarily long. M a n y recent text-books also d o not refer t o t h e use of such calibrating instruments and, therefore, there is perhaps some justification for presenting in t h i s place a more complete account of their ‘ advantages a n d use. T h e i n s t r u m e n t ‘ illustrated here is in its general operation like others t h a t have been described, i. e., i t is a device for accurately measuring successive portions of water as they may be drawn from t h e burette under examination. I t differs, however, from t h e previous instruments by its using t h e two-way glass cock as a zero adjustment instead of t h e usual mark on t h e lower stem. The enlargement a t C may also be looked on as a n improvement, since i t furnishes a convenient place for attaching t h e clamp for holding i t a n d also permits t h e use of a rubber stopper for connecting t o t h e burette, which makes a more satisfactory joint t h a n t h e g u m tubing t h a t would otherwise h a r e t o be employed. All of t h e previously described pipettes of this sort have had a mark on t h e lower stem which served as a zero point, t o which t h e water was adjusted before a portion was drawn out of t h e burette for measurement a n d a t which t h e outflow was stopped when t h e pipette was emptied t o make room for t h e next portion from t h e burette. T h e accompanying figure will illustrate this form of pipette if a mark around
