DETERMINATION OF ACIDITY. 133 



whey produced therefrom by rennet. The author has slightly 

 modified 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 O'Ol 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 l-o'.o" C, and estimate the specific gravity and fat 

 as before. 



Add the degrees of gi'avity 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. . Roughly 

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

 the percentage of fat in the milk and in the whey will give the 

 curd actually obtained. 



Determination of Total Acidity — Lactic Acid. — The acidity 



of milk is determined by titration with alkali, using phenol- 



phthalein as indicator ; the author prefers to place 10 c.c. in 



a small beaker, add TO c.c. of phenolphthalein solution (0'5 



gramme per 100 c.c. of 50 per cent, alcohol), and titrate with 



N 



baryta or strontia till a faint pink colour equal to that pro- 



ducc'd l)y the addition of 1 drop of a O-l)! per cent, solution of 

 rosaniline acetate in 96 per cent, alcohol, is obtained. The 

 proci'dure should not be varied. 



Storch uses a solution of lime (lime-water), containing solid 

 bme as a standard alkali solution ; this remains constant in 

 composition, and is almost exactly twentieth normal. The 

 strength of the solution remains constant, as if any of the lime 

 is removed by carbon dioxide, more is dissolved ; its strength is 

 but little affected by ordinary variations of temperature. 



It is to be recommended for dairy use, as no precaution, except 

 to have an excess of lime in the bottle, is necessary. 



N 



(ienerally speaking, about 17 c.c. to 20 c.c. of — alkali is 



required ; each cubic centimetre of N alkali used per litre of milk 



N . 



is called 1° of acidity, hence a milk requiring 2 c.c. of .-^ solution 



for 10 c.c. will have 20" of acidity. 



M"(.'reath has devised a convenient form of apparatus for the 

 estimation of acidity (Fig. 12) ; he employs a caustic soda solu- 

 tion of such strength that each c.c. = 0"01 gramme of lactic acid. 

 Ten c.c. of milk, after the addition of phenolphthalein solution, 



