The Lactometer and Its Application. 107 



an inch of the top, and the lactometer is slowly lowered 

 therein until it floats; it is left in the milk for about 

 half a minute before lactometer and thermometer read- 

 ings are taken, both to allow the escape of air which 

 has been mixed with the milk in pouring it, prepara- 

 tory to the specific-gravity determination, and to allow 

 the thermometer to adjust itself to the tem- 

 perature of the milk. The lactometer should 

 not be left in the milk more than a minute 

 before the reading is taken, as cream will soon 

 begin to rise on the milk, and the reading, 

 if taken later, will be too high, as the bulb 

 of the lactometer will then be floating in par- 

 tially skimmed milk (24). 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. Ow- 

 ing to surface tension the milk in immediate 



FIG. 40. Spe- 



contact with the lactometer stem will rise cific-gravity 

 above the level of the surface in the cylinder, 

 and this must be taken into consideration in making the 

 readings. It is not necessary to read closer than one- 

 half of a lactometer degree in factory or dairy work. 



116. Time of taking lactometer readings. The spe- 

 cific gravity of milk should not be determined until an 

 hour or two after the milk has been drawn from the 

 udder, as too low results are otherwise obtained (Reck-, 

 nag el's phenomenon).' 1 The cause of this phenomenon 

 is not definitely understood; it may come from the es- 

 cape of gases in the milk, or from changes occurring in 



1 Milchztg. 1883, 419 ; bull. 43. Chem. Div., TJ. S. Dept. of Agriculture, 

 p. 191 ; Analyst, 1894, p. 76. See also Fleischmann and Wiegner, Jr. 

 f. Ldw., 1913, pp. 283-323. 



