200 



MILK 



number of cubic centimeters of normal alkali used for neutraliza- 

 tion of 100 c.c. of milk by 0.009. 



Titration of milk for acid content by means of accurate chem- 

 ical methods is accompanied by some sources of error. Some 

 chemists recommend diluting the milk with water to facilitate 

 recognition of the end-point. However, an error is introduced by 

 .the addition of water, because alkaline phos- 

 phates are more easily soluble in diluted than 

 in normal milk. On the other hand, if milk is 

 titrated undiluted, the end-point of phenolph- 

 thalein is not as sharp as in diluted milk and the 

 acid may be overestimated. By heating milk 

 some of the acid phosphates are precipitated 

 and the carbon dioxid gas is lost, with the result 

 that lower figures are obtained than when raw 

 milk is titrated. 



THE MILK SEDIMENT TEST 



Fig. 72 Spill- 

 man's acid-test 

 cylinder (Van 

 Slyke). 



A test for visible dirt or sediment in milk is 

 valuable in giving a general idea of the methods 

 practised in the production of the milk. Dirt 

 is a carrier of bacteria and, therefore, should be 

 kept out of milk as far as possible. Aside from 

 the possibility of introducing disease germs with 

 dirt, the flavor of milk and milk products is materially depreci- 

 ated by its presence. 



The insoluble matter which settles to the bottom in bottles or 

 which is shown to be present by filtration of milk does not repre- 

 sent the whole amount of dirt actually present, to be sure. A por- 

 tion of the dirt goes into solution and escapes detection. There- 

 fore any test for visible dirt has no claim to scientific accuracy^ 

 This is further emphasized by the variability in the amount of 

 soluble material contained in the polluting material. Cow manure 

 is unquestionably the most important factor in furnishing the 

 dirt that enters milk, although cow hairs and particles from food 

 and bedding are liable to be present. Consequently there will 

 be relatively more insoluble dirt in the milk when cows are stabled 

 and live largely on stored fodder than in spring and summer, 

 when succulent fodder is abundant. The feces, as a rule, are 

 softer in summer than in winter and contain more soluble material* 

 Any quantitative determination of insoluble dirt in milk is 

 not absolute, but only relative. However, practice has shown 

 that much can be accomplished by a regular test for milk sediment. 

 Dealers and butter and cheese makers have used a sediment test 



