TESTING BY THE LACTOMETER 139 



other than 60 R, next set the arrow on the sliding 

 portion of the rule opposite the per cent, of fat found 

 in the milk and read the total solids contained in the 

 milk corresponding with the corrected lactometer read- 

 ing or specific gravity. 



To illustrate, suppose the lactometer reading of a 

 sample of milk at 70 F. is 30 and the per cent, of fat 

 is 4. To correct for temperature and find what the 

 lactometer reading would be at 60 F., the lactometer 

 reading (30) is placed opposite the little arrow at 60 

 on the temperature scale. Then, looking at the point 

 of temperature 70, we find opposite this point 31.3, 

 which is the corrected or true reading. Next, we 

 place the arrow opposite the 4 per cent, mark, as the 

 milk contains 4 per cent, of fat, and then notice where 

 the point 31.3 (specific gravity), comes in contact with 

 the solids scale. It corresponds closely to 12.8, which 

 is the per cent, of total solids in the sample of milk 

 examined. Some practice with this slide-rule enables 

 one to work rapidly. 



Specific gravity of milk-solids. The following rule 

 has been proposed by Fleischmann for calculating the 

 specific gravity of milk-solids: Multiply the specific 

 gravity of the milk by 100, from the result subtract 

 100 and divide this result by the specific gravity of 

 the milk. Subtract the last result from the per cent, 

 of total solids in the milk and then divide by this re- 

 sult the per cent of total solids of the milk. This may 

 also be expressed by the following formula: 



Sp. gr. milk-solids= 



milk-solids 



milk-solids (rooXsp. gr.) 100 

 sp. gr. 



