98 Testing Milk and Its Products. 



should not be left in the milk more than a minute before 

 the reading is taken, as cream will very soon begin to 

 rise on the milk, and the reading, if taken later, will be 

 too high, as the bulb of the lactometer will be floating 

 in partially skimmed milk (23). In reading the lac- 

 tometer degree, the mark on the scale plainly visible 

 through the upper portion of the meniscus of the milk 

 should be noted. Owing to surface tension the milk in 

 immediate contact with the lactometer stem will rise 

 above the level of the surface in the cylinder, and this 

 must be taken into consideration in reading the degrees. 

 There is no need of reading closer than one-half of a lac- 

 tometer degree in the practical work of a factory or a 

 dairy. 



113. Time of taking lactometer readings. The specific 

 gravity of milk should not be determined until at least 

 three hours after the milk has been drawn from the udder, 

 as too low results are otherwise obtained (RecknageV s 

 phenomenon). 1 The cause of this phenomenon is not 

 definitely understood; it may come from the escape of 

 gases in the milk, or from changes occurring in the me- 

 chanical condition of the nitrogenous components of the 

 milk. The results obtained after three or four hours will 

 as a rule come about one degree higher than when the 

 milk is cooled down directly after milking and its specific 

 gravity then determined. 



114. Influence of bi-chromate on the lactometer reading. 

 When potassium bi-chromate is added to milk samples 

 to preserve them from souring (188), the specific gravity 



i Milchzeitung 1883, 419; Bulletin No. 43, Chem, Div., U.S. Department 

 Of Agriculture, p. 191; Analyst 1894, p. 76, 



