TRANSACTIONS OF THE SECTIONS. 41 



any effect except that of completing their translucency and improving 

 their appearance. 



" 3rd. When raised to a red heat in the air, they slowly combine with 

 oxygen, and yield the same products as the amorphous substances. 

 In all respects they comport themselves as the same carburets when 

 uncrystallized, except that, as might have been anticipated from their 

 hardness, they are far less susceptible of reaction. And hence a 

 specimen may be freed of uncrystallized powder by cautious heating 

 in the air, and subsequent washing with the common acids. 



" These facts, besides their bearing on geological and other questions, 

 prove that the only essential condition of the crystallization of a body 

 is, that its particles be slowly segregated from any previous condition 

 whatever. This will appear to be more important when it is recol- 

 lected, that in all former experimental crystallizations there seemed 

 to be txoo elements, or essential conditions, viz. slowness of separation 

 of particles, with the presence of fluidity in some form or other, as 

 the medium of their easy motion." 



Experimental Demonstration of the certain existence of Haloid Salts 

 in Solution. By Dr. George Wilson. 



It was observed that all previous attempts to decide the question, 

 whether haloid salts do or do not decompose water, when dissolved 

 in it, had afforded no certain results, since none of the methods em- 

 ployed yielded an experimentum crucis. The object of this paper was 

 to show, that though the inquiry had long been abandoned as hopeless, 

 a demonstration can be given of the persistent haloid condition of the 

 dissolved haloid salts of the electro-negative metals. The mode of 

 experimenting followed was based on an important difference between 

 the two great classes of metals. The electro-positive metals, as po- 

 tassium, sodium, zinc, iron, &c., dissolve in the hydracids with the 

 evolution of hydrogen, indicating thereby (according to the more sim- 

 ple theory of the change) an attraction for the radicals of the acids su- 

 perior to that of the hydrogen which they displace ; the electro-nega- 

 tive metals, on the other hand, do not dissolve in the hydracids, nor de- 

 compose them ; they cannot, therefore, displace hydrogen, but should be 

 displaced by it. As the halogens or salt radicals have thus a less attrac- 

 tion for the electro-negative metals than hydrogen has, this body may be 

 employed to decompose their haloid salts. The action of uncombined 

 hydrogen on the dissolved salts was shown to be not of itself decisive 

 as to their true state in solution, but its effect on them when evolved 

 from an hydracid affords an unequivocal experimentum crucis. Gold 

 and its terchloride were chosen as examples of an electro-negative 

 metal and its haloid salt ; and hydrobromic acid was taken as the de- 

 composing re-agent. In anticipating their action on each other, it 

 appeared that if the chloride of gold became by solution in water an 

 hydrochlorate of the oxide, it should not be decomposed by hydrobro- 

 mic acid, which has a less attraction for all metallic oxides than hydro- 



