Snt B. C. BEODIE ON THE CALCULUS OF CHEMICAL OPERATIONS. 839 



Group 3. — Symhols of Antimony, Bismuth, Tin, Zinc, Cadmium, and Silver. 



It is evident that if some property of matter were discovered which admitted of accu- 

 rate estimation, and which should vary with the gaseous density according to a known 

 law, we should be able to infer the density from this property. Now in the num- 

 bers which represent the relative specific heats of chemical substances certain remark- 

 able relations have been observed, which render it probable that general laws of tliis 

 kind will hereafter be discovered, connecting the gaseous density of chemical substances 

 with their specific heat, and which will aiFord a more solid foundation than we at pre- 

 sent possess for the construction of a complete system of theoretical chemistry. 



The law of Dulonq and Petit is the most important of these numerical relations 

 which has been as yet ascertained. This law may be regarded as an experimental truth, 

 and thus stated : 



If A, Ai, A2, A^ be the smallest weights of the elemental bodies formed by the 



decomposition of the unit of any chemical substance, and if h, A„ h^, ... h^ be the 

 specific heats of these elements, either in the liquid or solid condition, then 



AA=AjAi=A2A2= A„A„. 



AA 

 In the following Table the value of the ratio -j^ is given in the case of those elements 



of which the symbols have been considered, and of which the specific heats have been 

 experimentally determined, with the exception of the elements carbon, boron, and 

 silicon, which do not appear to satisfy the condition. But these substances affect several 

 allotropic forms, and have more than one specific heat ; and it is not improbable that 

 some variety of these elements may yet be discovered which shall conform to the law. 



In the last column A„A„ is assumed as the mean of the values given in the preceding 

 column, namely, 3-289. 



A. h. hk. _Ml-. 



Sulphur 16 0-2026 3-241 0-985 



Selenium 40 0-0837 3-348 1-018 



Iodine 63-5 0-0541 3-436 1045 



Bromine 40 0-0843 3-372 1-025 



Phosphorus 15-5 0-2120 3-285 0-999 



Arsenic 37-5 0-0814 3-052 0-928 



Hence if the specific heat, h, of an element be knoA^Ti, we are able, from the equation 



A A 3*289 

 A= -^-^= ^ ' to calculate the value of A. The reasons have already been given 



which lead us to assume, with a certain probability, that W being the density of the 



element, A=W, or =— ' or = — . Whence, if A be known, W is determined within 



2 4 



certain limits. 



Symbol of Antimony. — In the decomposition of the terchloride of antimony into 



6x2 



