228 GENERAL SCIENCE 



The following formula is often used to determine the per cent 

 of solids not fat. Remember, normal milk has an average of 8.2 

 per cent solids not fat. Test some of the milk you are using at 

 home. 



Formula for Finding the Total Amount of Solids in Milk. 



- + - + .14 = S.N.F. (Solids not fat.) 

 4 5 



Add 4 points to the lactometer reading for every degree above 

 60. 



,, f Lactometer reads 104. 



For example, suppose the 1 mu j /.oo 



( Thermometer reads 62. 



104+8 = 112 . 



G = specific gravity. 



F = butter fat. 



Multiply by .29, the corrected reading of the lactometer. 



.29 XI 12 = 32.48 specific gravity. 



The real specific gravity is 1.03248. 



Suppose the amount of fat in milk was 3.3 per cent. 



Then 



<?+^+.14 = S.N.F. ^+^+.14 = 8.92. 

 45 45 



Leach's Casein Test for Formaldehyde. To 2 tablespoonfuls of pure milk 

 add an equal volume of hydrochloric acid, containing about 1 per cent of 

 Fe 2 Cl 6 . Place in a basin of water so as not to burn the milk, and heat slowly, 

 stirring or shaking the contents constantly to break up the curd. When nearly, 

 but not quite, at boiling point, remove the heat. If a purple color shows any- 

 where on the sides of the test tube or dish, formaldehyde was used to preserve 

 the milk. 



Milk does not sour if preserved with formaldehyde; it rots. 

 Formaldehyde is very seldom found in milk. Occasionally a poor 

 grade of old milk will be found to have been preserved with it. 



Detection of Boron Compounds. Place 5 c.c. of pure milk in a watch 

 glass and acidulate slightly with 10 per cent HC1. Add five drops of turmeric 

 tincture, and evaporate to dryness over a water bath. A red color indicates 

 boric acid or other boron compounds. 



Detection of Bicarbonate of Soda. The ash of pure milk shows no effer- 

 vescence with HC1. Burn 10 c.c. of milk to a white ash in a porcelain or quartz 



