Stability of
Wijs
FRANK A. NORRIS
Solution for Iodine Number Determinatior
AND
ROBERT J. BUSWELL, General Mills, he., Minneapolis, Minn.
T H E Wijs solution is probably t,he most satisfactory for
1 general use in determining iodine numbers. Its more widespread utilieation is hindered mainly by its supposed difficulty of preparation and short life. The first objection is hardly valid if ohlorheis @able and if t,heanalyst is reasonably careful. The short life would appear to he a much more serious objection, since three standard references on fat a.nalytical methods specifically caution against using this solution when it is more than 30 days old ( I , d, 4). However, Hilditch (8) does not accept this view, and Wijs himself (6) claimsindefinitestability for t,he reagent. Previous experience by one of the present authors is in agreement with the two last-named investigators. Since a decision on the stability of Wijs solution wits eonsidered necessary in connection wit,h some analytical imrk, the authors measured the stability. of the reagent when stored a t room temperature in 250-ml. dark bottles. The solution was prepared in the standard manner and eont,ained 1.5% excess equivalents of iodine over chlorine. Linseed oil, stored in the ice box, was used as the test substrate. Over a tota] period of 505 days, the \Viis solution did not chanKe sufficiently to muse a measurable difference in the iodine number of the substrate. No measurable differences weze found when the reagent was t.aken from bottles that, had been previoudy opened. These fa& indicat,e the validity of storing the solution a year or more, if 8toraae is in small bot,t'les IThich are opened as needed.
An Aid
Bottle NO.
.
I.
Stability of Wijr Soluti
Age of Solution, DW.
Days Since Bottl Firet Opened
1
a
2
a
3
: I 4 I .i
-
5
TURE CITED
(1) .4:n. Oil Chem.Soc., Methods. 1941. (2) A ~ ofiois*l ~ ~ them., ~ . offieinl and ~ ~ ~ Methods, , t ~ t5thi ~ ed., P. 430, 1940. (3) Hilditch. T. P., "Industrial Chemistry of Fats and Waxes", p. 4s. London. BailliBre, Tindall h Cor, 1941. (4) Jarnieson. G. 5.. "Vegetable Fats and Oils", p. 843. New York. Reinhold Publishing Coip.. 1932. (5) Wijs, J . J. A , , Analyst. 54, 11-14 (1929). i2. ~~~~~~lseries, cherniorl K
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, ~ e~en ern^ ~ 31i11~. I ~~
roo.
in Ashina Certain Materials
SELMA L. BANDEMER A N D P. 1. SCHAIELE Chemistry Section, Michigan Agricultural Experiment Station, East Lansing, Mich.
THE . '
itshing of many products is often difficult and time. . eonsummg, as 1s evldenced by the number of procedures published for special materials ( 1 ) . This is especially true for substances that are finely ground, contain oil or fat, 01' have a high phosphoms-to-base ratio. For such materials, a simple Promdure which was rem& devised to .ash large volumes of liquid egg white (e) is suggested.
,
Table
This procedure consists of lining the crucible with filter paper, charring the material over a Meker burner in this lined crucible, moistening the char with a solution of magnesium chloride, and completing the ashing in a, muffle furnace. Filter paper of the ComeCt (Whatman xo,4o or is folded as for filtering, the tip of the cone folded back, and this truncated cone fitted into the crucible. This liner orevents local overheating because of the air space between it'and the crucible and permits the easy e m p e of the volatile materials,
since the charring proceeds sloivly from the outside toward the center. The charred mass tends to retain its cone shape and is free of the crucible. Thus, the crucible malls are protected from the action of the materials ashcd. Fatty materials burn more evenly and slowly, without spattering. The char is moistened with a solution of magnesium chloride added dropwise over the entire and %shed in a m u ~ overnight e at The tLsh obtained is light, fluffy, and voluminous and dissolves readily in dilute hydrochloric acid on heating.
c,
this procedure, materials ,vhich have high If phosphorus-to-base ratio fuse on ignition to glassy mass which frequently entraps carbon that can then be burlled vi,ith great difficulty. This fusion is caused by the conversion of the dihydrwen and monohydrogen phowh*tes upon ignition to the metaphosphate (J), which does not dissolve readily in hot dilute hydrochloric acid. I n the suggested procedure, magnesium chloride supplies base t o produce the tertiary phosphate which is unaffected on heating t o 600" c. ash . Doorlv I n the authors' exaerienee., samples . . if thev do not ample base ;or the phosphorus or in the case-of plant matwid if t,h.hest,alks, stems, hullf, coatines, . , o'l bran have heen removed. In these materials, the use of the lined crucible and ~
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