DAIRY PRODUCTS. 51 



arc a day or more old than pure butter. The analytical data, however, 

 are too meager to permit a definite statement of this kind. Should it 

 prove to be true, it would be a valuable indication in the discrimatiou 

 between pure and adulterated butters. An examination of the old 

 disks with the microscope did not reveal a crystalline structure, and 

 this change, therefore, must be attributed to a molecular modification 

 or superficial oxidation. 



EFFECT OF THE PRELIMINARY HEATING OF THE FAT TO DIFFERENT 



TEMPERATURES. 



A butter fat was melted at a low temperature and allowed to stand 

 until the temperature had fallen to 30 0.; it was still perfectly fluid. 

 The disks were formed by dropping on ice as usual. The melting point 

 obtained was 33 C. The fat was now heated to 50 C. and treated as 

 above; melting point, 33.4 0. The temperature was then raised to 

 80 C. ; melting point, 320.8 C. 



The above results, falling within the possible error of observation, 

 show that the temperature to which the fat is subjected before the for- 

 mation of the disks has no appreciable effect on the point at which the 

 fat particle becomes a sphere. 



EFFECT OF SUDDEN RISE OF TEMPERATURE. 



A sudden rise of temperature t<*nds to greatly lower the melting point, 

 A fat which showed a melting point of 35.3 C. when determined in the 

 usual way, melted at once into a perfect sphere when dropped into the 

 water-alcohol mixture having a temperature of 29 C. At 28.5 C. the 

 globule was irregular. 



A disk of neutral lard, having by the usual method a melting point 

 of 42.4 0., became at once a sphere when dropped into the water-alcohol 

 at 36.2 0. Below that temperature the spheroidal shape was not sym- 

 metrical. 



In all cases this phenomenon will appear. It may be suggested, 

 therefore, with strict propriety, whether this may not be regarded as 

 the proper melting point. Since the temperature at which the sphe- 

 roidal state is assumed can be determined within one or two degrees by a 

 preliminary trial, it would not be difficult to have a series of mixtures 

 of water and alcohol arranged so as to show differences of temperature 

 of 0.5 C. By dropping the disks successively into these mixtures the 

 instantaneous fusing point could be determined with accuracy. 



The method set forth in the preceding pages has been proved by 1G5 

 determinations to be capable of giving agreeing results. Not only will 

 Uic numbers obtained by the same observer be concordant, but also 

 those of different analysts. This arises from the fact that the moment 

 of the assumption of the spheroidal state is easily determined even by 

 an uupracticed eye. I have also noticed that in this condition pure 

 butter and oleo are quite transparent, while on the other hand neutral 



