﻿130 MEIGS ON THE RELATION OF 



elastic force, on the contrary, is exceedingly great ; while cold alone, or a pressure of 

 but four atmospheres is sufficient to condense chlorine. The expansive power of 

 hydrochloric acid gas, is equal to the pressure of 40 atmospheres, at the temperature 

 of 50°. Now the atomic heat of H is 21-2064 ; of CI, 14-4627 ; and of HC1, 28-9263. 

 Four volumes of HC1 must contain as many atoms as two volumes of H, or of CI ; 

 or, two volumes of HC1 contain as many atoms as one volume of H or CI. But one 

 volume of H contains half an atom, hence one volume of HC1 must contain one-fourth 

 of an atom, which must therefore be surrounded by twice as large a heat-sphere as 

 the half-atom of H. Such facts authorize us to conclude, that chlorine in combining 

 with hydrogen has its specific gravity reduced, in consequence of abstracting from the 

 latter gas an additional quantity of caloric, by which its particles are separated further 

 from each other and made to occupy a larger bulk. This supposition will also account 

 for the change in elasticity. The union of iodine, bromine, cyanogen, &c, with hydro- 

 gen is accompanied by a similar reduction in specific gravity, and alteration in physi- 

 cal and chemical properties. When hydrogen unites with sulphur, phosphorus, and 

 arsenic-vapors, and with carbon, in different proportions to form, respectively, sul- 

 phuretted, phosphuretted, arseniuretted, and light and heavy carburetted hydrogen 

 gases ; with oxygen to form aqueous vapor, and with nitrogen to produce ammonia, 

 the resulting specific gravities of these respective compounds is very much less than 

 the sum of those of their constituent elements, The volume and elastic force of these 

 gases are also altered in a remarkable manner. 



According to Graham, the more nearly bodies agree in composition, they are the 

 more likely to act as solvents of each other, or to be miscible in the liquid form.* But 

 we have seen that in both compound and elementary bodies of the same atomic con- 

 stitution and of like chemical constitution, the specific heats are in the inverse pro- 

 portion to the atomic weights. In this connection, I may refer to those numerous 

 and interesting examples of change in the solubility of bodies after being heated 

 although their composition remains the same. Alumina, binoxide of tin, sesquioxide 

 of chromium, and other metallic peroxides, and certain salts, such as silicates, tung- 

 states, phosphates, antimoniates, &c, after exposure to a temperature just below red- 

 ness, lose their solubility in acids. In its cubic form, the bisulphuret of iron resists 

 the action of both air and water ; but in its right rhombic form, when exposed to 

 moist air, it absorbs oxygen with great avidity, and is converted into a crystalline 

 mass of copperas.f Spontaneous ignition often accompanies those changes in solubility, 

 and generally just as the body is passing from the soluble to the insoluble state. " Je 

 crois meme que ce changement de chaleur specifique correspondant a un changement 

 d' agregation, donne l'explication d'une phenomene bien connu des chimistes et des 

 physiciens, je veux parler de rincandescence qui se manifeste subitement dans certains 



* Elements, p. 142. -j- Kane. 



