11)2 Mr. M. M. Pattison Mui 



r on. 



ditious of equilibrium of the system : — 



Sodium chloride q =0'62 Hydrochloric acid p =0*38 

 Sodium sulphate q l =0*29 Sulphuric acid ... p l — 0'll 

 Sodium oxalate q 2 =0*10 Oxalic acid p 2 =0'90 



Of the remaining systems considered the more important 

 are : — 

 4. Si/stems consisting of gaseous substances arising from, the 



dissociation of a solid ; and 5. Systems consisting entirely 



of gaseous substances. 



If a gas M be an addition compound of the form # A + /3B 

 + 7C, then, by dissociation, one molecule of this gas will be 

 resolved into a molecules of A, /3 molecules of B, and 7 mole- 

 cules of C. If, further, p, q, and r be the amounts of the 

 different components in unit volume, and if the most general 

 case be considered, in which, besides the amounts present of 

 p, q, r (the dissociated constituents of M), an amount P of 

 the original compound is also present, then the equation of 

 equilibrium is deduced, 



j>yt»=*[p+F(0]. _• • • • • (?) 



This equation is also applicable to cases in which indifferent 

 gases, other than A, B, or C are present. The equation is 

 developed and applied by the authors especially to the results 

 of experiments upon the dissociation of N 2 4 into N0 2 where 

 the product of decomposition of the original compound is alone 

 present, and to the dissociation of HI in presence of either of 

 the products of decomposition (see Deville and Troost, Compt. 

 Rend. 1875, and A. Naumann, Berl. Ber. x. 2045 ; see also 

 Lemoine, Ann. Chim. Phys. [5] xii. 145). 



In his earliest paper (Pogg. Ergzsbd. viii.) Ostwald de- 

 scribes the experimental method which he has adopted, viz. 

 measurement of the change in specific volume of a liquid ; 

 and shows that it is possible by this method to measure small 

 amounts of chemical change occurring between those sub- 

 stances solutions of which are mixed to form the liquid in ques- 

 tion. Thus, if the specific volumes of normal solutions of potas- 

 sium sulphate and of nitric acid be determined, if these solu- 

 tions be mixed, and if the specific volume of the mixed liquid 

 be then determined, it is found that a certain amount of expan- 

 sion has taken place, and that this expansion measures the 

 amount of chemical action which has occurred*. Ostwald 



* K. Hofmann (Pogg. Ann. exxxiii. 575, 1868) seems to have been the 

 first who attempted to deduce measurements of chemical change from 

 determinations of sp. vol. and of coefficients of refraction. His attempt, 

 however, was not altogether successful. 



