Citric acid content of milk

Citric acid content of milk

Feb., .Igq.] CURRENT TOPICS. 347 ROBERT FEAKON, of New Test for Cyanic Acid-W’IrmAb~ Trinity College, Dublin, Ireland (jour. Biol. Chem., 1926, 70,...

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Feb., .Igq.]



ROBERT FEAKON, of New Test for Cyanic Acid-W’IrmAb~ Trinity College, Dublin, Ireland (jour. Biol. Chem., 1926, 70, 785792), has devised the following test for cyanic acid and its salts. The reagent is prepared by addition of two to five drops of a 6 per cent. solution of benzidine in alcohol and several drops of a 6 per cent. solution of cupric acetate to 5 C.C. of water, and mixing. The cyanate solution, which must be either neutral or faintly acid, is added to the reagent. A purple color develops, and1 rapidly changes into a sepia precipitate, which soon deposits. This test will reveal the presence of 0.1 milligram, and even less, of potassium cyanate. Alkalies inhibit formation of the colored compound; certain compounds interfere with the test, acids decompose the colored compound and hydrolyze the cyanate, sulphates precipitate the benzidine, and cyanides, thiocyanates, thiosulphates, iodides, and bromides react with the reagent to form dense colored precipitates. The precipitate yielded by cyanates contains one copper atom, two cyanate radicals, and one benzidine molecule: its formula is : Cu(OCN),.NH,.C,H,.C,H,.NH,, both amino groups being in the para position. The reaction may be used for the quantitative determination of cyanates, collecting the precipitate on a filter, washing with water and alcohol, and drying. This test cannot be applied directly to the solution obtained on digestion of urea with urease, since urease interferes with the reaction. However, if the digested solution be treated1 with an excess of normal silver nitrate solution, a precipitate is produced. If this precipitate be. mixed with the cyanate reagent, and the mixture be carefully acidified with tenth normal hydrochloric acid, the characteristic cyan&e reaction is obtained, showing that silver cyanate was present i;l the precipitate, and that a cyanate was one of the products formed during the enzymic hydrolysis of urea. J. S. H. Citric Acid Content of Milk. F. F. SHERWOOD and B. W. HAM?MER (Agric. Exp. Station Iowa State College of Agric. attd Meclzanic Arts Research Bull. No. 90, 19-39, 1926) have determined the citric acid content of 335 samples of milk obtained from 20 individual cows, including five Jerseys, three Guernseys, seven The cows were on pasture during the Ayrshires, and five Holsteins. summer and received a liberal supply of silage in the winter. The citric acid content of the milk ranged between 0.07 and 0.33 per cent., was not influenced with an average of 0.18 per cent.; it apparently by the season, the stage of lactation, the time of day of milking, or the breed. In these 335 samples of milk, the acidity, calculated as lactic acid, ranged between 0.10 and1 0.25 per cent. with an average of 0.17 per cent., the ash between 0.38 and 1.10 per cent. with an average of 0.70 per cent., the fat between 1.60 and 9.20 per cent. with an average of 4.58 per cent., the total solids between 8.82 and 20.15 per cent. with an average of 13.52 per cent. When the total solids were calculated as the sum of one-fourth the lactometer reading plus VOL. 203, No. 1214-24




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1.2 times the fat, the calculated value tended to be higher, rather than lower, than the value obtained by analysis. The citric acid content of 27 samples of cream obtained from a separator ranged between 0.9 and 0.19 per cent. with an average of 0.13 per cent., while the citric acid content of 26 samples of mixed farm cream ranged1 between 0.10 and 0.20 per cent. with an average of 0.15 per cent. No evidence was obtained of a seasonal variation in the citric acid content of cream. J. S. H. New Indicators .-BARNETT COHEN, of the Hygienic Laboratory, U. S. Public Health Service (Public Health Reports, 1926, 41, 3051-3074)) describes six new compounds of the sulphonephthalein series which are of value as indicators in volumetric analysis and as reagents for the calorimetric determination of hydrogen-ion concenThe new compounds have the following scientific names, tration. proposed common names, useful pH range, and color change in passing from acid to alkaline : Tetrabrommetacresolsulphonephthalein (brom cresol green), 3.8 to 5.4, yellow to blue; Tetrachlormetacresolsulphonephthalein (chlor cresol green), 4.0 to 5.6, yellow to blut ; Dibromphenolsulphonephthalein (brom phenol red), 5.2 to 6.8, yellow to red ; Dichlorphenolsulphonephthalein (chlor phenol red), 4.8 to 6.4, yellow to red1 ; Dibromdichlorphenolsulphonephthalein (brom-chlor phenol blue), 3.0 to 4.6, yellow to blue ; Metacresolsulphonephthalein (metacresol purple) with a dual pH range and color change, i.e., 1.2 to 2.8, red to yellow, and 7.4 to 9.0, yellow to purple. J. S. H. Faught Test for Acetone.In this test, the unknown solution is mixed with an aqueous solution of sodium nitroprusside. Then several drops of an aqueous solution of ethylene diamine hydrate are added as an upper layer. If acetone be present, a pink or red zone forms at the line of contact. The solution of sodium nitroprusside HARRY J. SCHAEFFF;R, of the Philadelphia must be freshly prepared. College of Pharmacy and Science (Am. Jour. Pharmacy, 1926, 98, 643-645), has studied the relative sensitivity of the various tests for He finds that the Faught test is the most efficient and acetone. delicate, and is of extreme value when small quantities of acetone are He reports the delicacy of the various tests for to be detected. acetone as follows : Dibenzalacetone I : 500, Lieben I : 1000, Kolthoff J. S. H. I : 2500, Legal I : 10,000, Faught I : IOO,OOO. Professional Engineers. More Than 3000 in United States Civil Service.-The United! States Civil Service Commission has just issued an interesting pamphlet which describes the work of engineers There are more than 3000 in the Federal executive civil service. civilian professional engineers in the Government’s employ. Federal engineering operations are carried on in practically every part of the United States, and extend to Alaska, Guam, Hawaii,