PHYSICAL 



29 



is allowed to stand for one hour to eliminate air bubbles, it 

 will be found to have a density somewhat lower than that 

 taken subsequently (Recknagel's phenomenon). This pecu- 

 liarity has been investigated by several observers. Vieth con- 

 firmed Recknagel's results and found the average rise to be 

 +1.3° (water = 1000). H. Droop Richmond ^^ reports that in 

 70 per cent of his experiments the rise varied from 0.3° to 1.5° 

 averaging 0.6°, and that in 30 per cent of the observations no 

 rise in density was indicated; also that the rise was more 

 rapid at low temperatures than at high temperatures. H. D. 

 Richmond, from consideration of experiments made in con- 

 junction with S. 0. Richmond on the effect of heat upon the 

 density and specific heat of milk, regards the phenomenon as 

 largely due to the increase in density of the fat on solidification. 

 Changes in the milk sugar, cessation of expansion of the case- 

 inogen, absorption of gases, and enzyme action have also been 

 suggested as causes of this phenomenon but cannot be regarded 



Table VIII 

 EFFECT OF TEMPERATURE ON VOLUME 



as satisfactory. Various data confirming Richmond's hypoth- 

 esis were obtained by Toyonaga, and Fleishmann and Weig- 

 ner.^* The latter observers found that the change in density 

 was proportional to the amount of butter fat present. Micro- 

 scopical examinations also showed that the solidified globules 

 were of greater density than the liquid globules at the same 

 temperatures. 



