﻿124 MEIGS ON THE RELATION OF 



meme corps peuvent done changer completement avec la temperature."* Changes in 

 the form of a body correspond to variations in its combined heat. 



Many crystallizable bodies assume a peculiar state of aggregation known as the 

 vitreous condition, which may be considered as a variety or modification of dimorphism. 

 The binarseniate and biphosphate of soda resemble each other strongly in physical 

 and chemical properties. When exposed to the same heat, the first solidifies, on 

 cooling, into a white opaque mass composed of interlaced crystalline fibres, while the 

 second is converted into a transparent, colorless glass. While undergoing these 

 changes, the arseniate discharges sensibly more heat than the phosphate; hence, 

 probably, the glassy condition of the latter salt is due to the retention around its 

 particles of a portion of the heat of fluidity.-]" 



Ordinarily sugar has a granular or crystalline structure. When melted and allowed 

 to cool slowly, it assumes a glassy condition and manifests very different physical 

 properties. If, while still soft and viscid, (as at the temperature of 100°,) it be rapidly 

 drawn out into threads, a large quantity of heat is liberated,' and the sugar separates 

 into minute granules of a pearly lustre. 



That the vitreous condition is in some manner connected with the amount of heat 

 accumulated around the ultimate particles, is shown by the fact that glass kept soft 

 for a long time, gradually loses its heat and is converted into a substance known as 

 Reaumur's porcelain, in which it assumes different characters. The crystalline and 

 amorphous states of the same body differ to a certain extent in their properties; the 

 former being in general harder, specifically heavier and less soluble than the latter, 

 in which the atoms are placed farther apart than in the first. Graham also affirms 

 that the amorphous condition is accompanied by a larger quantity of combined heat 

 than the crystalline. 



Arsenious acid sublimes as a transparent glass with a light, yellow tint. By 

 exposure, the vitreous mass gradually changes into a congeries of small octohedral 

 crystals, and becomes opake, milk-white, and slightly altered in solubility and density. 

 According to H. Rose, if the vitreous mass be dissolved in hydrochloric acid, each 

 crystal as it separates emits a flash of light. Regnault, in his second memoir, says, 

 "l'acide vitreux (arsenious) devient promptement opaque a la temperature de 100°." 

 The vitreous acid has an atomic heat of 15.0796; the opaque, 15.2064. Now, 

 Guibourt has shown that the specific gravity of the vitreous acid diminishes during 

 the change to the opaque form, from 3.785 to 3.695; and that the latter dissolves 

 rather more abundantly both in hot and cold water than the transparent. This is an 

 exception to the ordinary cases, for the change from the amorphous to the crystalline 

 form is accompanied generally with increased density and diminished solubility. It 

 is interesting here to observe that the difference in atomic heat, though very small, is 



* Regnault. f Graham's Elements, p. 151. 



