108 Testing Milk and Its Products. 



the mechanical condition of the nitrogenous compo- 

 nents of the milk. The results obtained after a couple 

 of hours will, as a rule, come about one degree higher 

 than when the milk is cooled down directly after milk- 

 ing and its specific gravity then determined. 



117. Influence of solid preservatives on lactome- 

 ter readings. When potassium bi-ehromate, corrosive 

 sublimate, etc., is added to milk samples to preserve 

 them from souring (190), the specific gravity of the 

 milk will be increased ; with the quantity usually added 

 (% gram to a pint of milk) the increase amounts to 

 about 1 lactometer degree, and this correction of lacto- 

 meter readings should be made with milk samples pre- 

 served in this manner. To avoid this error, Dr. Eich- 

 loiP recommends the use of a solution of potassium bi- 

 chromate in water (43 grams to 1 liter), the specific 

 gravity of which is 1.032, or similar to that of average 

 milk;- 5 cc. of this solution is required for a pint of 

 milk. No correction is necessary for the dilution with 

 this small amount of liquid preservative. 



118. Cleaning the lactometer. The lactometer should 

 be cleaned directly after using, by rinsing with cold 

 water; it is then wiped dry with a clean cloth and 

 placed in the case. 



n8a. Testing the accuracy of lactometers. The 

 correctness of lactometers may be determined with a 

 fair degree of accuracy by placing them in different 

 salt solutions prepared by dissolving exactly 3, 4, and 5 

 grams of pure dairy salt in 100 grams (cc.) of water. 

 The specific gravities at 60 F. of solutions thus ob- 



l Technik der Milchfriifung, p. 98. 



