CHAPTEE VI. 

 THE LACTOMETER AND ITS APPLICATION. 



106. The Quevenne lactometer. This instrument (see 

 Fig. 38, next page) consists of a hollow glass cylinder 

 weighted by means of mercury or fine shot so that it will 

 float in milk in an upright position, and provided with a 

 narrow stem at its upper end, inside of which is found a 

 graduated paper scale. In the better forms, like the Que- 

 venne lactometer shown in the figure, a thermometer is 

 melted into the cylinder, with its bulb at the lower end 

 of the lactometer and its stem rising above the lactometer 

 scale. 



The lactometer is used for the determination of the 

 specific gravity of milk. The term specific gravity means 

 the weight of a certain volume of a solid or a liquid sub- 

 stance compared with the weight of the same volume of 

 water at 4 C. (39.2 Fahr.); for gases the standard of 

 comparison is air or hydrogen. If the milk which a can 

 will hold weighs exactly 103.2 fibs., this can will hold a 

 smaller weight of water, say 100 Ibs., as milk is heavier 

 than water ; the specific gravity of this milk will then 

 be Jff 2 - = 1.032. 



The specific gravity of normal cows' milk will vary in 

 different samples between 1.029 and 1.035 at 60 F., the 

 average being about 1.032. 



107. The lactometer enables us to determine rapidly 

 the relative weight of milk and water. Its application 

 rests on well-known laws of physics: When a body 

 floats in a liquid, the weight of the amount of liquid 



