174 EXPERIMENT STATION RECORD. 



" Casein takes up acids from dilute solutions. For example, 1 gm. of casein, 

 shaken with 100 cc. of N-1000 hydrochloric acid for 3 hours, takes from the 

 solution nearly 50 per cent of the acid. The amount of acid thus taken up is 

 not definite and fixed, but varies (1) with the concentration of the acid, (2) 

 with the duration of contact until equilibrium is reached, which requires some 

 hours, (3) with the degree of agitation until equilibrium is reached, (4) with 

 the temperatux'e, and (5) with the kind of acid. Some acid is always taken 

 up, however small the amount of acid used ; but the acid is never completely 

 removed from the solution, however large the propoi'tion of casein present. . . . 



" The maximum amount of acid adsorbed by a gram of casein varies almost 

 dli'ectly with the concentration of the acid within the limits used (N-125 and 

 N-1000) in the case of hydrochloric, lactic, and acetic acids, so that at equilibrium 

 the ratio of acid in 1 gm. of casein to the acid in 1 cc. of surroiuiding solution 

 is nearly constant. In the case of sulphuric acid the ratio increases with dilu- 

 tion of acid. The equilibrium ratio reached when 1 gm. of casein is treated 

 with 100 cc. of N-500 solution at 0°, is 675 for sulphuric acid, 147 for hydro- 

 chloric, 80 for lactic, and 36 for acetic. Equilibrium is reached in 2 to 24 hours, 

 according to (1) the acid used, (2) the temperature, and (3) the degree of 

 agitation. The greater part of the acid reacting is generally taken up in the 

 first half hour or hour. Increase In temperature increases the rate at which 

 equilibrium is approached, but decreases the final amount of acid taken up, 

 when solution of casein does not result at the higher temperature. . . . 



" The acid taken up by casein ma.v be extracted by shaking with water. The 

 extraction continues until the equilibrium ratio (concentration of acid in 1 gm. 

 of casein divided by concentration <»f acid in 1 cc. of surrounding solution) is 

 established, and then ceases. . . . 



"Neutral salts (potassium chlorid and magnesium sulphate) are not ad- 

 sorbed from dilute solution by casein. 



" The behavior of casein with dilute acids, when no solution occurs, suggests 

 three different explanations : (I) an adsori)tion compound, (2) solution of acid 

 in casein, or (3) a hydrolyzable salt of casein. A careful api)licati()n of the 

 experimental rosults to each of these hypotheses indicates that the action ap- 

 pears to correspond in detail only with the characterisics which apply to an 

 adsorption. 



" On the basis of this explanation, the pi'oteid precipitated when milk sours 

 Is free casein in which lactic acid is held by adsorption." 



The hydrolysis of the sodium salts of casein, L. L. and D. D. Van Slyke 

 (Neio York Htatc ^tu. Tech. Bui. J, pp. 15Jf-162, figs:. 2). — "In determining the 

 amount of alkali neutralized by casein, different indicators give different re- 

 sults. Phenolphthalein has been in most common use in such work, giving 

 higher results than other indicators. The object of the work presented was to 

 determine the neutral point by means of conductivity measurements in compari- 

 son with the use of phenolphthalein and alkali. Our results Indicate that the 

 sodium salts of casein hydrolyze so readily that titration with alkali does not 

 give the true equivalent weight of the proteid. An >excess of casein, as of 

 phosphoric acid, is required to overcome the alkalinity of the hydrolyzing nor- 

 mal salt. The point at which the alkalinity is overcome is indicated by the 

 attainment of mininunn conductivity and corresponds roughly with the point 

 neutral to phenolphthalein. Because of the extreme weakness of its acid 

 properties, markedly greater excess of casein Is required to give an acid reac- 

 tion with less delicate indicators." 



The numerical determination of leucocytes in milk, A. R. AVard, Margaret 

 Henderson, and C. M. Haring (Bicn. Rpt. Bd. Health Col. 19 (1905-6), pp. 

 lJi2-15C)). — The methods which have been proposed for the enumeration of 



