REPORT OF THE CHEMIST. 



G9 



under which the sample of milk is obtained are known, the number 

 expressing its density is not conclusive in respect of its genuineness. 



This is a question, however, which has been most thoroughly dis- 

 cussed in connection with official control of the sale of milk, and it 

 would not be profitable to reopen the argument. 



(2) Volume of cream. — The volume of cream which a given milk will 

 afford depends ou many conditions. Among the causes which deter- 

 mine the variation may be mentioned distance and time of transporta- 

 tion, shape of vessel in which the milk is placed, temperature, and time 

 allowed for the cream to rise. On account of these causes of variations, 

 milks taken from the same cow and under conditions as nearly as pos- 

 sible show marked variations in the volume of cream produced. I have 

 also noticed that milks bought at random from the dealers do not show 

 so large a volume of cream as those which are presented for the purpose 

 of analysis. As an illustration of this, reference is made to the table of 

 analyses of milks obtained from Higby. These were purchased from the 

 milk-wagon each morning, and the driver did not know they were for 

 analysis. The mean per cent, of cream by volume is 7. 



On the other hand, the milks furnished by Smith were known to be 

 used for analysis. The mean volume per cent, for the two sets is 14J. 

 These significant facts show, the importance of having complete control 

 of the feeding and milking the cows in the subsequent studies of the 

 Department in this direction. In fact, I may add that the value of 

 milk analyses in determining a standard of comparison for American 

 milks depends chiefly on such a supervision as I have mentioned. 



(3) Fat. — The percentage of fat in a milk is not always proportionate 

 to the volume of the cream. Therefore the determination of the lat or 

 ether extract gives a better index of the butter-making value of the 

 milk than is afforded by the volume of the cream alone. Inasmuch as 

 the real market value of a milk depends largely on its content of fat, 

 the numbers given in the preceding tables for the fat per cents will 

 be studied with interest. It appears that the percentage of tat in 

 American milk (107 analyses) is not far from 5. 



Solids not fat. — When milk is evaporated to dryness and the water- 

 free residue weighed the percentage of total solids is obtained. If the 

 percentage of fat is subtracted from this number the percentage of 

 "solids not fat" is given. This percentage is nearly a constant quan- 

 tity, and in average milk is not far from 9.2. When the number falls 

 below 9 it is fair to presume that the milk has been watered or is of an 

 inferior quality. 



It would be out of place here to go into further details concerning the 

 analysis of milk and its adulteration. This subject will be presented at 

 a subsequent time in the form of a special report. 



EEPORT OF THE ASSISTANT CHEMIST. 



Bureau of Chemistry, Department of Agriculture, 



Washinoton, I). C, September 11, 1884. 

 SiR: I have the honor to submit for publication in the Annual lie- 

 port of the Department for 1884 the following synopsis of the work of 

 the past year which has been carried on under my direction. 

 Thanking you for the sincere support you have given me in the work, 

 I am, very respectfully, 



CLIFFORD RICHARDSON, 

 Dr. H. W. Wiley, Assistant Chemist. 



Chemist. 



