January 15, 1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
centrated sulfuric acid and 2 cc. of perchloric acid in microKjeldahl flasks on an electric heater until colorless and the excess of perchloric acid has been driven off. The perchloric acid is added in 0.5-cc. portions, one after the sulfuric acid, the second to the cooled flask after the charring is quite decided, and the remaining portions if, and as, needed. The digestion requires from 30 minutes to 2 hours, When the digestion is complete, the contents of the flask are transferred t o a 150-cc. beaker, the flask is rinsed two or three times with small volumes of distilled water, the liquid cooled, and the acidity adjusted by the addition of concentrated ammonium hydroxide from a dropping bottle until just alkaline to litmus (a very small piece of litmus paper may be kept in the solution), then made just acid with concentrated sulfuric acid and an excess of from 5 to 10 drops of acid added. One cubic centimeter of the mercaptoacetic acid reagent is added and the solution made strongly alkaline by the addition of 1 to 2 cc. of concentrated ammonium hydroxide. The colored solution thus formed is compared with a series of standards in narrow tubes (12 X 20 mm.); therefore the volume should be kept below 20 cc. If the volume is too large for these tubes, other tubes of uniform diameter and appropriate capacity, such as Nessler tubes, may be used. TABLEI. RESULTSOF IRON DETERMINATIONS BY MERCAPTOACETIC ACID METHOD SAMPLE
VOLUME IRON ADDED IRON FOUND
cc Goat’s milk A Goat’s milk A Goat’s milk B Goat’s milk B Goat’s milk C Goat’s milk C Goat’s milk D Jersey COW’B milk Jersey cow’s milk Milk from local market
.
5 5 5 5 5 5 5 5 5 5
QTam
Dried miIk Dried milk Dried milk Dried milk
0.563 0.507 0.584 0.577
Hog’s bloodb Hog’s bloodb
0.020 0.01c
Hog’s bloodb
0.02d
cc .
Mg.
Mg. 0.0035,0.0035
0 665 0.008+
0.004--,0.0040 003 0.006540.003,0.0035 0 003 0.006 0.0035,0.003,0.003 0.0035,O.004 0:003 0.0065 0.0035 0.003.0.003 -
: :...
... ..... ....
... ... ... ... ...
0.0058 0.0056 0.0058 0.0059 0.01C0,0.0104 0.0050, 0.0053 0.0053,0.0052 0.0054,0.0052 0.0052 0.0100,0.0103 0.0104,0.0104
IRON^
Mg./-
100 cc.
0.07
0.06+ 0.08-
0.07+ 0.065 0.06
0.0063 0.075 0.07 0.06 1.03 1.10 0.995 1.02 51.0 52.3
... ... ...
52:s
Guinea pig’s bloodb 41.0 0.28 0.080,0.086,0.0S0 Guinea pig’s bloodb 0. If 0.045,0.045,0.045 45.0 Guinea -Die’s O.lf 41.5 0.02 0.06. 0.063 - bloodb a The added iron was subtracted before the calculation of mg. per 100 and the results are for 100 cc. excepting in the case of dried milk where they are for 100 grams. b See also section “Comparison with Other Methods.” Measured with blood.pipet. d 2 cc. of 1 to 100 dilution. e 2 00. of 1 to 10 dilution. f 1 CC. of 1 to 10 dilution.
The standards for color comparison are prepared by the substitution of 1 to 5 cc. of appropriate standard iron solutions for the sample to be analyzed. The entire procedure in the preparation of the colored standards must be identical with that for the sample. The standards occasionally fade within an hour; however, the color is satisfactorily restored if the solution is then shaken with air. Standards are often satisfactorily revived even after they have been allowed to stand for 24 hours or more. It is, however, advisable to replace some of the members of the aeries of standards every day to verify the values of the older aolutions. Table I gives results obtained by the application of this procedure to goat’s milk, cow’s milk, and milk powder. DETERMINATION OF IRON IN BLOOD. Samples of 0.01 or 0.02 cc. of blood are taken with the blood pipet, transferred with dilution to the micro-Kjeldahl flasks, and digested with 1 cc. each of concentrated sulfuric and perchloric acids. The remainder of the procedure is the same as described above.
47
Table I includes data for determinations on hog’s blood by this procedure, and by using 1-and 2-cc. portions of a 1 to 100 dilution, and also data from some earlier experiments with guinea pig’s blood in which amounts equivalent t o 0.1 and 0.2 cc. were taken from a 1 to 10 dilution. In the latter case, the final volume of the colored solutions was 25 cc. and the colors were compared in the colorimeter. COMPARISON WITH OTHER METHODS. Kennedy’s thiocyanate method applied to the sample of guinea pig’s blood, ranging from 0.1 to 0.4 cc., with and without added iron, gave results which when calculated for 1-cc. samples are 0.42, 0.39, 0.40, 0.395, 0.435, and 0.414 mg., respectively. The average is 0.412 mg., compared with an average of 0.423 mg. for nine determinations by the mercaptoacetic acid method, which are given in the table. Hog’s blood was used for a macrodetermination of iron by the digestion of 25-cc. samples with 60 cc. of concentrated sulfuric acid, dilution, reduction of the ferric iron to ferrous by pure zinc, and titration with standard permanganate solution. The iron found was 13.375 and 13.350 mg., respectively. Calculated for 100-cc. samples, the average is 53.75 mg., compared with 52.0 mg. for the mercaptoacetic acid method (Table I). OTHERAPPLICATIONS.This method was applied to eggs and to feces. Because of the larger quantities of iron the procedure for milk was modified as follows: two-gram samples were used, the product of digestion was diluted to 50 cc., and 10-cc. aliquots were used for color development without the adjustment of the acidity prior to the addition of the mercaptoacetic acid reagent. Either tubes or the colorimeter may be used. SUMMARY The mercaptoacetic acid method for the determination of small amounts of iron has been adapted to the analysis of milk and blood. ’ Wet-ashing with sulfuric acid and perchloric acid has been found satisfactory and avoids the contaminations and losses encountered in the dry-ashing procedures. ACKNOWLEDGMENT The authors desire to express their appreciation to Paul E. Howe for advice during the progress of the work and to A. K. Besley for the samples of milk. LITERATUBE CITED Andreasch, Rudolph, Ber., 12, 1391 (1879). Claesson, Peter,lbid., 14,412 (1881). Elvehjem, C. A., J. Bid. Chem., 86, 463 (1930). Ginsburg, J., and Bondzynski, S., Bet-., 19,116 (1886). Henriques, Valdemar, and Roche, Andree, Bull. SOC. chim. biol., 11, 679-92 (1929). (6) Kennedy, R. P., J. Biol. Chem., 74, 385-91 (1927). (7) Lematte, L., Boinot, G., and Kahane, E., J. pharm. chim., 5, (1) (2) (3) (4) (5)
325-31, 361-73 (1927).
( 8 ) Lorber, Leo, Biochem. Z., 181,391-4 (1927). (9) Lyons, Edward, J. Am. Chem. SOC., 49,1916-20 (1927). (10) Neumann, A., Z. phyaiol. Chem., 37, 115 (1902); 43, 32 (1904). RECEIVED November 18, 1932.
JAPAN TO MANUFACTTJR~ SILICON CARBIDE.Large-scale production of silicon carbide is proposed by Japanese interests, according to the Department of Commerce. Last ear Japan’s imports of “mineral substance for grinding or polistin amounted to 3120 metric tons, valued at 939,000 yen, of whicfihe United States supplied approximately 50 per cent. Annual consumption of silicon carbide in Japan is approximately 1000 metric tons. Two Japanese companies have started production on a commercial basis, and it is expected that their combined output will materially reduce imports of artificial abrasives.
