244 THE CHEMICAL CONTROL OF THE DAIRY. 



and of detecting the somewliat hypothetical case of scientific 

 skimming and watering. 



A very important rule, which is of great use in the control 

 work of the dairy chemist, may be enunciated as follows : — 



The specific gravity of a milk in lactometer degrees 

 added to the percentage of fat will remain constant, whether 

 the cream has been diminished or increased. The sum of 

 the two will be lowered by the addition of water. For 

 instance, the original milk had a specific gravity of r032& 

 or 32"5°, and contained 4 per cent, of fat. The sum is,, 

 therefore, 36 '5. 



If a sample of (say) series (2) were found to have a specific 

 gravity of 1"0315 or 31 '5°, and contained 5"0 per cent, of fat, the 

 sum would be still 36'5. 



If the sample had a specific gravity of 1'0335 or 33 '5°, it will 

 be found that the fat amounted to only 3"0 per cent., and the 

 sum would be 36 '5. 



If the sample, however, contained only 3'8 per cent, of fat, 



and had a specific gravity of 31 "5°, the sum would be only 35'3 ; 



and it could then be concluded that the milk had been watered^ 



35 '3 

 and that it contained only ;^^^ X 100 = 97 per cent, of the 



original milk, or, in other words, 3 per cent, of water had been 

 added. 



It has been found that this rule holds with remarkable accuracy 

 for any percentage of fat between and 10, and it is not very 

 far out with even higher percentages of fat. 



It must not be expected that the sum of the lactometer 

 degrees and fat will always add up to the same identical 

 figure, as there is a liability to error in both determinations ; 

 with care, however, the difference due to this cause should not 

 exceed 0"5. 



The value of the samples of series (3) lies in the fact that 

 rising of cream is most easily detected by their percentages of 

 fat being considerably difierent from that in series (1), as the 

 total effect due to this cause is usually marked. 



The Solution of Analytical Prolblems. — A dairy chemist is 

 frequently called upon to solve the most diverse problems with 

 regard to milk and its products. In the following paragraphs 

 a few such problems are given, together with the analytical 

 data from which the solution was deduced. They cover a fairly 

 wide range, and may be taken as fairly representative of the- 

 questions a dairy chemist is called upon to elucidate. All are 

 actual examples. 



Problem I. — To determine to what the low specific gravity of 

 the milk is due. 



