82 FOODS AND FOOD ADULTERANTS. 



scale marked to 45 C. The principle of the apparatus is based on the 

 fact that at 30 to 35 0., 100 parts of water will dissolve 36 parts of salt. 

 The operation is carried on as follows : Mix G2.5 grams of milk with 

 20.25 grams of salt and add 15 grams of litmus tincture, saturated with 

 salt, to color the milk. Eaise the temperature to 30 to 35 0., shake 

 thoroughly, and then place the apparatus so that all the undissol ved salt 

 will fall into the under-graduated stem of the apparatus. Each degree 

 of the scale corresponds to 62.5ui gr. of the salt. The part undissolved 

 subtracted from the total quantity will give the quantity dissolved, from 

 which the quantity of water is easily calculated. 



The lactometer of Geissler 1 is too complicated for ordinary use, and 

 the method of estimating the water content of milk by measuring the 

 volume of whey filtered from the coagulated albumens proposed by 

 Zenueck 2 does not afford sufficiently exact results to merit further 

 description. 



SPECIFIC GRAVITY. 



The specific gravity of a milk diminishes as its content of fat increases, 

 and hence within certain limits it may be a valuable index of the char- 

 acter of the sample under examination. 



When the cream has been removed, however, the specific gravity may 

 be reduced to that of normal milk by the addition of water, and then 

 the determination of the specific gravity alone is not a certain method 

 of detecting adulteration, yet it is a valuable indication and should al- 

 ways be determined. 



This determination may be made by any of the methods already de- 

 noted for fats and oils or by a hydrometer. Since the use of this latter 

 instrument (lactometer, lactodeusimeter) is easy and speedy, it is gen- 

 erally employed instead of the slower but more exact procedure with a 

 picnometer. 



Martin 5 found the average specific gravity of the milk from fifty cows 

 from E. B. Brady's farm, Westchester, K Y., to be 1.03101. From 

 another lot of thirty one cows, farm of Peter Knox, it was 1.03149; from 

 sixteen cows, farm of George Nelson, 1.03175. 



Jenkins 4 makes the following observations respecting the values of 

 the specific gravity determination: 



A consideration of the observations noticed above brings ns to the following con- 

 clusions with regard to the value of total solids, and of specific gravity, as criteria for 

 judging of the quality of milk. 



We have seen that pure herd-milk shows very wide variations in its content of 

 solids and fat, and varaitions less striking in its specific gravity. No instance appears 

 to be on record where a competent observer has found for the mixed milk of a num- 

 ber of healthy cows a specific gravity less than 1.029, and we may conclude with cer- 

 tainty that milk which falls below that density has been watered. 



] Ber. Chem. Gesel., Vol. 10, p. 1272. 



2 Vieth, Milch priifungsmethoden, p. 87. 



3 Fourth Ann. Kept., N. Y. State Bd. of Health, pp. 429 etseq. 



4 Kept. Conn. Exp. Sta., Vol. 10, pp, 88, 89. 



