178 THE ESTIMATION OF PROTEINS. 



and Bosworth's method is to place 20 c.c. of milk in a 200 c.c. 

 flask, add 100 c.c. of water, 1 c.c. of phenol-phthalein solution, 



N 

 and titrate with sodium hydroxide solution till a faint pink 



colour appears ; raise the temperature to between 18 to 24 C., 



N 

 and add acetic acid in 5 c.c. portions, shaking vigorously after 



each addition, till the casein separates in the form of white 

 flakes ; usually 25 c.c. are sufficient, but the addition of acid 

 should be continued, 1 c.c. at a time, after 25 c.c. have been 

 added, till on standing a short time the liquid appears quite 

 clear. Water is now added to make up 200 c.c., the contents 

 of the flask shaken vigorously, poured upon a dry filter, and 

 the whole of the filtrate collected. Of the filtrate, 100 c.c. 



N 

 are titrated with sodium hydroxide solution till a faint pink 



colour appears, care being taken that the shade of pink is the 

 same as that obtained before (a colour standard, see p. 179, 

 may usefully be employed). A second titration may be made 

 with 50 c.c. of the filtrate, the results being doubled. The 

 percentage of casein is deduced by subtracting the number 

 of c.c. of sodium hydroxide solution used per 100 c.c. of the 

 filtrate from half the volume of the acetic acid added and multi- 

 plying by 1 -0964. 



The method works well with fresh milk, but milk that is suffi- 

 ciently sour to coagulate on boiling does not give satisfactory 

 results. 



Estimation of Curd.- Lindet proposed deducing the amount 

 of curd from the difference of specific gravity of milk and the 

 whey produced therefrom by rennet. The author has modified 

 slightly his method to the following : 



Estimate the specific gravity and fat in the milk by any con- 

 venient method ; to 100 c.c. of milk add 0-01 gramme of rennet 

 powder, and keep at 42 C. till curdled ; cut up the curd, and 

 allow it to settle, and strain off the whey through muslin ; cool 

 the whey to 15-5 C., and estimate the specific gravity and fat 

 as before. 



Add the degrees of gravity and the percentage of fat in the 

 milk, and subtract the sum of the degrees of gravity and the 

 percentage of fat in the whey ; the difference divided by 3-5 will 

 give the percentage of dry curd available for cheese-making. 

 This will, of course, be very much less than the pressed curd 

 actually obtained, as this not only contains a considerable per- 

 centage of water, but also the bulk of the fat in the milk. Eoughly 

 speaking, the dry curd multiplied by 4 plus the difference in 



