198 CLEAN MILK 



is about 1,030 to 1,034. This is shown in practice by floating the 

 lactometer in milk, placed in a cylindrical glass tube, when it will 

 sink in the milk to a mark on the stem corresponding to the specific 

 gravity of the milk. The greater weight of milk (as compared 

 with water), or its specific gravity, is due to the solids-not-fat it 

 contains, i. e., the casein, albumin and milk sugar. While the lacto- 

 meter may be used to determine the solids in unaltered milk as it 

 comes from the cow, it will not determine the solids in milk which 

 has been watered and skimmed. Milk fat weighs less than water,, 

 and, of course, less than milk. Removing cream raises the specific 

 gravity of milk. Then if water were added the specific gravity- 

 might be lowered again to the normal for untampered and un- 

 adulterated milk. 



To estimate the solids in milk by the lactometer, the tempera- 

 ture of the milk should theoretically be 6o° F. But the milk may 

 be at any temperature between 50 and yo° F. providing a correc- 

 tion is made for the temperature of milk above or below 6o° F. 

 Thus, if the milk is above 6o° F., one must add to the lactometer 

 reading 0.1 for each degree of temperature above this point; if the 

 temperature of the milk is below 6o° F., one should subtract 0.1 

 from the lactometer reading for each degree of temperature below 

 this point. For example, if a sample of milk at a temperature of 

 65 ° F. shows a lactometer reading of 29, then one should add to this 

 reading: — 5 X 0.1 = 0.5, which gives the corrected reading as. 

 29.5. If, on the other hand, the lactometer should float in milk to a 

 mark on its stem indicating 29, and the temperature of the milk 

 was 55" F., then one should subtract o. 1 for each degree of tem- 

 perature below 6o° F. from this lactometer reading, which gives 

 us 28.5 as the corrected reading. 



Now, to estimate the solids in milk we must have previously 

 determined the percentage of fat in the milk by means of Feser's 

 lactoscope or the Babcock machine. To find the total solids in 

 milk we divide the lactometer reading by 4, and, to the result, add 



