23 



Difference between milk taken and dry solids = water + vola- 

 tile substances. 



Good milk should have 12.5 per cent, of solids. 



Determination of ashes and phosphoric acid : The residue 

 from the determination of solids is then heated first over a small 

 flame, and finally at a dull-red heat, until complete incineration is 

 effected. It is advisable to incinerate, if possible, in a muffle. 

 The dish is then covered, and allowed to cool in the desiccator, and 

 finally weighed. 



Platinum dish + cover -\- ashes, 

 Less platinum dish + cover. 



Leaves ashes. 



The ashes ^of milk vary from 0.5 to 0.75 per cent. More than 

 0.75 per cent, found in an analysis would indicate the addition of 

 alkalies, which are frequently used during the hot season in the larger 

 cities to retard souring. The reaction of such ashes is then alkaline, 

 and will show effervescence on the addition of acid. The ashes of 

 normal milk show a neutral reaction, and do not effervesce with 

 acids. 



The phosphoric acid is easily and accurately determined by 

 the following method : In the manner stated above, 50 c.c. milk are 

 dried and incinerated. The salts are then dissolved with some 

 hydrochloric acid, and the solution is brought to 20 c.c. To 10 

 c.c. of the cold solution, ammonia or caustic soda is added until 

 the reaction of the fluid has become alkaline. This is then acidi- 

 fied with acetic acid. The solution thus treated contains but 

 little acetates, which would interfere with the deltcacy of the end 

 reaction of ferrocyanide of potassium and uranium. To this solu- 

 tion a standardized solution of uranium is added. When the pre- 

 cipitate ceases to increase, the whole is boiled for a few minutes, 

 and one drop of the clear supernatant liquid is brought on a porce- 

 lain plate, and tested with a solution of ferrocyanide of potas- 

 sium. A brown coloration indicates the presence of an excess of 

 uranium solution, which, however, may disappear again on con- 

 tinued boiling. The addition of uranium solution is continued 

 until the reaction remains. It is of advantage to make two titra- 

 tions at a time, using in one 0.5 c.c, between the tests, and in the 

 other, 0.1 c.c. 



