210 VARIATION IN SPECIFIC GRAVITY. 



the percentage of water or cream, the divisions on the 

 scale are so minute, while the latter marks them so 

 that they can be read off with greater ease and pre- 

 cision. 



For the purpose of showing the difference in the spe- 

 cific gravity in different specimens of pure milk, taken 

 from the cows in the morning, and allowed to cool down 

 to about 60, I used the latter instrument with the fol- 

 lowing results : The first pint drawn from a native cow 

 stood at 101, the scale being graduated at 100 for pure 

 milk. The last pint of the same milking, being the strip- 

 pings of the same cow, stood at 86. The mixture of the 

 two pints stood at about 93. The milk of a pure-bred 

 Jersey stood at 95, that of an Ayrshire at 100, that 

 of a Hereford at 106, that of a Devon at 111, while a 

 thin cream stood at 66. All these specimens of milk 

 were pure, and milked at the same time in the morning, 

 carefully labelled in separate vessels, and set upon the 

 same shelf to cool off; and yet the variations of specific 

 gravity amounted to 25, or, taking the average quality 

 of the native cows' milk at 93, the variations amounted 

 to 17_ 10 . 



But, knowing the specific gravity, at the outset, of 

 any specimen of milk, the hydrometer would show the 

 amount of water added. This cheap and simple instru- 

 ment is therefore of frequent service. 



The lactometer is a very different instrument, and 

 measures the comparative richness of different speci- 

 mens of milk. It is of very great service both in the 

 butter and cheese dairy, for testing the comparative 

 value of different cows for the purposes for which they 

 are kept. This instrument is very simple and cheap 

 and the practical dairyman can tell by it what cows he 

 can best part with without detriment to his business. 



