SPECIFIC GRAVITY. 83 



alteration of tlie dimensions of the Ijulbs by the expansion of 

 the enclosed air, caused by rise of temperature. It is plain, 

 that the gravity of the bubble, determiaed at 60° F., does not 

 represent the actual gravity of the fat at the temperature 

 at which the experiment is made, but requires a certain 

 correction. 



The mode of manipulation finally adopted was as follows : — 

 Into the test tubes containing the melted fat are fitted 

 corks, bored with holes, through which are fitted pieces of 

 glass rod, with rounded ends, long enough to dip a quarter of 

 an inch or more below the surface of the fat. The bubbles 

 are held by means of the glass rods, below the surface of the 

 fat, and by this means surface adhesion, which would affect 

 the results, is avoided. 



The tubes being suitably supported are now immersed in 

 water, at about 100° F., contained in a beaker; the beaker is 

 itself immersed in another containing water at the same 

 temperature. The whole arrangement is very slowly heated 

 upon the said bath, until the bubbles are seen to detach 

 themselves from the rods. They faU very slowly, but there 

 is no difficulty in observing when the first Une of separation 

 is formed. 



The following results obtained by Mr. Wigner are given as 

 an illustration of the reliability of the method adopted : — 



The clean melted butter-fat was weighed according to 

 Dr. Muter's suggestion at 100° F. and 135° F. 

 Specific gravity at 100° F. compared with 



water at 60° F 907-2 



Corresponding to "actual density" at 100° F. 



compared with water at 1 00° F. ... 912-1 



Specific gravity at 135° F. compared with 



water at 60° F 895-2 



Corresponding to "actual density" at 135° F. 



compared with water at 1 35° F. ... 906-7 



