The Lactometer and its Application. 95 



108. Influence of temperature. Like most liquids, milk 

 will expand on being warmed, and the same volume will, 

 therefore, weigh less when warmed than before; that is, 

 its specific gravity will be decreased. It follows then 

 that a lactometer is only correct for the temperature at 

 which it is standardized. If a lactometer sinks to the 

 32-mark in a sample of milk of a temperature of 60 F., 

 it will only sink to, say 33, if the temperature of the 

 milk is 50 F., and will sink farther down, e. g., to 31, 

 if the temperature is 70 F. Lactometers on the market 

 at present are generally standardized at 60 F., and to 

 show the correct specific gravity the milk to be tested 

 should first be warmed (or cooled, as the case may be) 

 to exactly 60 F. As this is a somewhat slow process, 

 tables have been constructed for correcting the results 

 for errors due to differences in temperature (see Appen- 

 dix, Table V). 



109. As the fat content of a sample of milk has a 

 marked influence on its specific gravity at different tem- 

 peratures, the co -efficient of expansion of fat differing 

 greatly from that of the milk serum, the table cannot 

 give absolutely accurate corrections for all kinds of milk, 

 whether rich or poor. But the errors introduced by the 

 use of one table for any kind of whole milk within a 

 comparatively small range of temperature, like ten de- 

 grees above or below 60, are too small to have any im- 

 portance outside of exact scientific work, and in such, 

 the specific gravity is always determined by means of a 

 picnometer or specific gravity bottle, at the temperature 

 at which this has been calibrated. In taking the spe- 

 cific gravity of a sample of milk by means of a lacto- 



