RECENT WORK IN AfxRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY— AGROTECHNY. 



Studies relating to the chemistry of milk and casein, L. L. Van Slyke and 

 A. W. BoswoRTii (Neio York State Sta. Tech. Bui. 37 (1914), pp. 11; Jour. 

 Biol. Chcm., 19 (1914), Nos. 1, pp. 67-71, 73-76; 3, pp. 397, 398).— This bulletin 

 consists of three parts, as follows: 



I. The cause of acidity of fresh milk of coics and a method for the detennina- 

 tion of acidity (pp. 4-6). — '"The acidity of fresh milk is due to the presence 

 of acid phosi)hates. Titration of phosphoric acid with alkali, in the presence 

 of calcium salts, results in hydrolysis of dicalcium phosphate formed during 

 the titration, whereby free calcium hydroxid and phosphoric acid are first 

 formed and then calcium hydroxid unites with more dicalcium phosphate to 

 form insoluble tricalcium phosphate. As a result of these reactions more alkali 

 is required to make a solution, containing calcium and phosphoric acid, neutral 

 to phenolphthalein than is required in the absence of calcium. The calcium 

 must be removed previous to titration by trentment of 100 cc. of milk with 2 cc. 

 of saturated solution of neutral potassium oxalate"." 



II. The phosphorus content of casein (pp. 7-10). — "The amount of phos- 

 phorus in casein has been commonly given as about 0.S5 per cent. By treating 

 a solution of casein in dilute NHiOH with ammonium oxalate and an excess of 

 NH4OH and letting stand 12 hours the phosphorus content is reduced to about 

 0.7 per cent. This lower percentage can not be explained as being due to 

 hydrolysis of casein and splitting off of phosphorus. While some of tbe casein 

 is hydi'olyzed, this portion does not enter into the final preparation and does 

 not affect its composition, because the hydrolyzed portion is not precipitated 

 by acetic acid while the unhydrolyzed part is. The higher figure ordinarily 

 given is due to the presence of inorganic phosphorus (dicalcium phosphate) 

 carried from the milk into the precipitated casein and not entirely removed 

 under the usual conditions of preparation. The lower figure corresponds very 

 closely to two atoms of phos^ihorus (0.60S per cent) in the casein molecule. 

 Analyses of various preparations of casein containing varying amounts of ash 

 show a general correspondence between the ash and phosphorus content." 



III. The action of rcnnin on casein (pp. 10, 11). — This study was made for 

 the purpose of determining whether the change from casein to paracasein is 

 accompanied by cleavage of any of the elements contained in the casein 

 molecule. The use of an excess of ammonia commented on by Harden and 

 McCallum (see p. 607) was not found to result in the loss of phosphorus due 

 to cleavage of the casein molecule. " The similarity between the composition 

 of casein and paracasein, and the fact that casein has been shown to have 

 a molecular weight of 8,SS8+ and a valency of S, while paracasein has been 

 shown to have a molecular weight of 4,444+ and a valency of 4. seems to be 



"Amor. Jonr. riiysiol., (1013), No. 5, pp. 265-278. 



606 



