THE FUSING POINT. 35 



tion, the second, which melts only when the temperature 

 rises to 31 or 32. If the liquid formed by fusion at this 

 point be kept for some hours at a temperature not varying 

 more than two or three degrees on either side of 31 32, it 

 becomes opaque, a great part solidifying as crystals, the third 

 modification, which retain their opacity till the temperature 

 rises to 40 or upwards, according to the length of time at 

 which the substance has been kept at a temperature about 

 31 32." The author has "reason to regard the crystals 

 formed in this manner as identical with those deposited in 

 an ethereal solution of butter, which melt at from 53 to 57, 

 according to their state of purification." 



After being heated to upwards of 60 and solidified by 

 cooling below 20, pork fat melted at 27 28; passing 

 into the second modification, it melted again at 37 38. 

 Long-continued heating near this temperature converts a 

 small proportion of this substance into the third modifica- 

 tion, so that any consequent elevation of the melting point 

 of the mass cannot be determined with precision. 



Mutton fat, after an exposure to a temperature presumed 

 to be higher than any of its melting points, and subsequent 

 solidification at a temperature presumedly below all of them, 

 melted at 39, solidifying again while the temperature rose 

 slowly to 52 53, where it melted a second time, and when 

 kept for some hours within a range of temperature not 

 exceeding 3 on either side of the melting point, solidified 

 again, and then melted only when the temperature rose to 

 57. It thus solidified only when the temperature fell 

 below all three melting points, unless the cooling were much 

 retarded. In all cases the temperature at which solidification 

 takes place determines the modification, and consequently 

 the melting point of the substance. 



Dr. Dupre" and others, as well as we ourselves, have 

 pointed out the effect continued heating has upon the 



