162 ANALYTICAL EDITION Vol. 1, No. 3

days the total biochemical oxygen demand for carbonaceous substances is not equal to the theoretical oxygen demand of the substance. Urea, however, shows complete oxidation.

Table I-Comparison of Biochemical Oxygen Demand with Theoreti- cal Oxygen Demand of Pure Substances

SUBSTANCE PER CENT OF THEORETICAL OXYGEN DEMAND IN 30 DAYS AVERAGE

Lactose 82.5, 69.0, 80.5, 67.5 75 .0 Starch 87.5, 78.7 83 .0 Cellulose (Elter paper

Whatman KO. 1) 78.0, 69.0 71 .0 Sodiumhalmitate 75.0, 81.0 78 .0 Peptone" Urea Sodium oleate (20 days)a

a Unpublished data of E. L. Pearson, of this laboratory.

Conclusions

82 .5 100.0 76 .0

of the theoretical oxygen demand depending on the sub- stance.

2-The biochemical oxygen demand of urea in 20 days is equivalent to the calculated theoretical oxygen demand.

3-The rate of deoxygenation of a sample containing any of the carbon compounds studied follows the equation of a first-order reaction.

4-Compounds containing both carbon and nitrogen show two-stage oxidation, the first of which fits the above equation. Urea, showing no carbon oxidation, gives a curve which ap- pears as the second-stage oxidation curve.

Literature Cited

(1) Greenfield, Elder, and McMurray, IND. EKG. CHEM., 18, 1276 (1926). (2) Mohlman, Edwards, and Swope, [bid., 20, 242 (1928). (3) Standard Methods for Water Analysis, 6th ed., 1925, A. P. H. A. (4) Theriault, U. S. Pub. Health Service, Pub. Health Bull. 173, App. 111, Oxygen demand Of carbonaceous sub-

stances in 30 days is equivalent to from 70 to 85 per cent p. 163 (1927).

Note on the Recovery of Platinum'

G . J. Hough

BUREAU OF CHEMISTRY AND SOILS, %'ASHINGTOZI, D. c.

HE following method for the recovery of platinum and al- T cohol from the filtrates and residues obtained in methods involving the use of platinic chloride for the determination of potassium has been in use in the soils laboratories for several years and has proved very convenient and satisfactory.

In order to recover the platinum and alcohol in the filtrates, obtained from washing the chloroplatinates, about 1 gram of ammonium chloride crystals is added to each 300 cc. of fil- trate, the mixture stirred well, allowed to stand until clear, and filtered.

If the 80 per cent alcoholic solution with the platinum were allowed to stand before the addition of ammonium chloride, a slow reaction with the formation of platinum black and acetone would occur and render the alcohol unfit for use and difficult to purify. Hence, precipitation should be made a t once after filtering. The alcoholic solution may be allowed to accumulate until a suitable quantity for rectification is obtained. If it is distilled to one-fourth of its original volume, the distillate will consist of 83 to 85 per cent alcohol suitable for re-use.

The ammonium platinic chloride obtained above, together with the chloroplatinate residues from the potassium deter- minations, is dissolved in hot water, and a few cubic centi- meters of hydrochloric acid (1:2) are added. The solution is heated nearly to boiling, and magnesium powder is added gradually until a slight excess is present. After the platinum salt has been completely decomposed, concentrated hydro- chloric acid is added slowly to dissolve the excess magnesium, the solution is boiled several minutes, and the platinum black filtered off and washed well.

The recovered platinum is transferred to a porcelain dish, dissolved in aqua regia, and evaporated to a thick paste. The paste is treated three times with hydrochloric acid and evapo- rated nearly dry after each addition of acid; finally, it is taken up with hot water and a few drops of hydrochloric acid, fil- tered, and made up to the volume employed in making deter- minations.

Experience has shown that the loss of platinum by this method of recovery is very small. A solution of platinic chloride after two years' use, involving more than two hundred

1 Received February 27, 1929.

determinations and seven to eight recovery treatments, was found to have lost only 200 mg. of platinum. Consequently, the loss of platinum in each determination was less than one- fourth of a cent.

Simple Graduated Wash Bottles' Earle R. Caley

PRINCFTON UNIVERSITY, PRINCETON, N. J.

N analytical investigations it is sometimes desirable to know I the amount of fluid employed in washing precipitates. This is, indeed, necessary where a given precipitate exhibits a slight solubility in the washing medium used. In such cases a fairly accurate measure of the amount of wash liquid used must be made in order t o apply the necessary correction for the slight amount of precipitate lost in the washing operation.

Two simple forms of graduated wash bottles, which the writer has found to be serviceable for this purpose, are shown in the illustration. The one, constructed from a suitable-sized graduate, is most convenient in those cases where a cold wash- ing fluid is employed; while the other, constructed from a large test tube which has been calibrated and etched, is necessary where a hot washing medium must be used. In the latter case a turned wooden base is provided in order to main- tain the apparatus upright on the working table.