RECKNAGELS PHEXOMENO^. 



75 



TABLE IX. — For Correcting Specific Gravity of 

 Separated Milk to 60° -F. 



The author has devised a scale for correcting the specific 

 gravity of milk to 60° F. It is usually engraved on the " milk- 

 scale," and is used by adjusting the specific gravity found (on 

 the slide) to the arrow at 60° F. The corrected specific gravity 

 is found opposite the temperature at which the determination 

 was made. 



The corrected specific gravities obtained by the " milk-scale " 

 agree generally within 0-1 of those taken from the table. At 

 very low temperatures, however, there is sometimes a larger 

 difference. 



S. H. Collins has devised a milk scale in which the temperature 

 correction for specific gravity is automatically made ; the points 

 denoting temperature and specific gravity observed are brought 

 together, and on the other side of the scale the percentage of 

 solids not fat corresponding to any percentage of fat is read off. 



The Rise of Specific Gravity of Milk on Standing. — 

 Milk drawn from the udder contains a large number of air bubbles, 

 and its specific gravity cannot be taken ; after the expiration of 

 an hour or so these have disappeared, and a specific gravity 

 determination is possible. It was first observed by Recknagel 

 that the specific gravity taken after the expiration of one hour 

 was lower than the specific gravity subsequently obtained. He 

 found the rise in specific gravity to be regular, more rapid at 

 low temperatures than high ones, and to amount on the average 

 to 0-001. lie attributed the change to an alteration in the 

 volume of the casein. 



Vieth completely confirmed Recknagel's observation, and 

 found the average rise to be 0'0013 ; Bourcart also observed the 

 phenomenon. 



The author has studied Eecknagel'-s phenomenon (as this 



