ADULTERATION WITH WATER. 69 



For the above reason a few of the best processes are 

 here outlined. These apply only to cow's milk. 



(i) The method proposed by Leze and Hilsont is to 

 determine the time required to produce coagulation in a 

 known quantity of milk by the action of rennet. This 

 method gives at the same time a means of judging some- 

 what as to the freshness of the sample. Upon unadul- 

 terated fresh milk at 35 degrees C, rennet reacts in forty 

 minutes when added in the proportion of i :io,ooo, that 

 is, one liter of rennet will cause ten thousand liters of 

 milk to curdle in forty minutes when the temperature is 

 35 degrees. In this process a solution of good commer- 

 cial rennet is used, one c. c. of it being added to 100 c. c. 

 of milk. 



With the above proportions (i :ioo), pure milk coagu- 

 lates in three minutes and eleven seconds. When 10 per 

 cent of water is added it requires three minutes and four- 

 teen seconds, and with 50 per cent of water, five minutes 

 and forty-nine seconds. If the time of coagulation ex- 

 ceeds 3 min. 50 seconds, the addition of water or some 

 alkaline preservative is evidenced. On the other hand, if 

 the milk coagulates in less than two minutes it evidently 

 was not fresh, the sudden curdling being due to incipient 

 decomposition. Such milk is unfit for use as food. 



(2) For this purpose of detecting the admixture of 

 water to milk, Lescoeur suggests coagulating the sample 

 with rennet and determining the density of the serum 

 at 15 degrees C, and also the total dry matter contained 

 in it. The density of serum of pure milk varies from 

 1.029 to 1.03 1, and the dry matter per liter varies from 

 67 to 71 grams. The addition of four per cent of water 

 diminishes the density about 0.00 1, and the dry matter 

 about two grams per liter. In making comparisons the 

 following table may be used : 



