CHAPTER IX. 
THE DETERMINATION OF THE MELTING AND SUBLIMING 
POINTS OF MINUTE PARTICLES OF MATERIAL. 
The determination of the melting point of a compound is 
usually one of the simplest and most reliable tests at our dis¬ 
posal for ascertaining the purity of a known compound or for 
obtaining an idea as to the probable nature of a substance of 
unknown composition. In the case of organic compounds the 
melting point is one of the first constants to be ascertained and 
even with certain inorganic substances a melting point deter¬ 
mination may often prove of great value. 
It not infrequently happens that such a small quantity of 
material is available that the usual laboratory methods are im¬ 
practicable and recourse must be had to some microscopic 
method of procedure. Often, the chemist deals with material 
containing a large proportion of amorphous matter mixed with a 
crystalline substance and a satisfactory separation cannot be 
effected; or again, a preparation is obtained in which there 
appears to be two or more different crystalline substances but 
no means for separating them can be found. In all these cases 
a melting point would give the needed information were it possible 
to effect a separation. 
By spreading out the material in a thin layer upon an object 
slide and examining the preparation with the microscope, we can 
almost always find crystals or fragments of material here and 
there not in direct contact with others, but appearing in the 
image isolated and free. We have thus in reality effected a 
separation and if we apply heat, we should be able to make 
reliable observations upon the behavior of each isolated particle. 
If in addition we have some means of controlling and measuring 
the heat applied, it is obvious that a melting point can be ascer¬ 
tained. Inasmuch as a variety of methods for temperature 
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