MANUAL OF GENERAL AGEICULTUEE. 109 



The specific gravity of (milk) solids is determined by 



t 

 the following formula : S== 



100s 100 

 t 



s 



S being the specific gravity of the milk solids, s that of 

 the milk and t the total solids of the milk. 



Example: A sample of milk has been found to con- 

 tain 13. per cent of total solids, sp. gr. 1.032 ; then 

 100s 100 100x1.032100 



=3.101; t this or 13. 3.101 

 s 1.032 



13. 

 =9.899; then dividing t by this, - =1.31, the specific 



9.899 



gravity of milk solids. Let the teacher furnish samples 

 of normal, watered, skimmed and watered-and-skimmed 

 milk and the class determine each. 



82. TEST FOR CHEMICAL ADULTERATION OF 

 MILK. 



Materials: Salicylic acid, formalin in samples of 

 milk, ether, surphuric acid, alcohol, iron chlorid solution, 

 hydrochloric acid, evaporating dish. 



(a) Salicylic Acid. To 20 c.c. of milk add from 2 

 to 3 c.c. sulphuric acid and 4 to 5 c.c. ether and stir in 

 an evaporating dish. Evaporate and treat the residue 

 with about 3 c.c. alcohol, add a few drops of iron chlorid 

 solution and heat again. A deep violet color will be ob- 

 tained in the presence of salicylic acid. 



(b) Formalin (Formaldehyde). To one-fourth test 

 tube of milk add an equal volume of water and 5 to 10 

 c.c. sulphuric acid used in testing. A violet ring is formed 

 at the junction of the two liquids if formalin is present ; 

 if not, a slight greenish tinge will be seen. The violet 

 color is not obtained with milk containing over .05 per 

 cent formalin. 



