Chemical Properties of Stannic Chloride. 



489 



cannot fail to be suggestive. At present it may be noted 

 that " where there exists an aptitude for directed decompo- 

 sition," such as is involved in the above dynamical cone jptic n, 

 and such as exists in the aqueous or alcoholic solution of 

 stannic chloride, there sulphuretted hydrogen at once precipi- 

 tates stannic sulphide ; whereas between the dry sulphuretted 

 hydrogen and stannic chloride there is found only a small 

 quantity of addition compound (SnCl 4 . 5H 2 S), which, when 

 agitated into a condition of instability by elevation of tempe- 

 rature, gives the stannic sulphide observed by Dumas. This 

 influence of alcohol on stannic chloride and sulphuretted hy- 

 drogen is typical of that of catalytic agents in general ; and 

 the explanation here suggested is of wide application. The 

 phenomena discovered by Prof. Dixon, to whom I am indebted 

 for a complete list of the published papers on the action of dry 

 substances, are of a parallel nature. He found that the com- 

 bination of dry carbon monoxide and dry oxygen, 



2CO + 2 =2C0 2 *, 



occurs only in the path of the spark, but that when the gases 

 are moist the combination is explosive. Again, Dixon has 

 shown that, in the combustion of carbonic oxide and hydrogen, 

 the influence of the steam is not of a physical but of a che- 

 mical nature f. The inactivity of dry hydrochloric acid and 

 dry oxygen, of dry hydrobromic acid and dry oxygen, and 

 their activity in the presence of water is of the same nature % 

 (Richardson). The observation, made by Pringsheim§, that 

 dry chlorine and dry hydrogen do not combine in sunlight, 

 but that the presence of a small quantity of water is sufficient 

 to determine their combination, is quite parallel. Baker has 

 proved that some dry solids are incombustible in dry oxygen, 

 though he finds that others are combustible ||. 



It cannot be maintained as a law of nature that no two pure 

 substances, AB, DC, combine ; either 



(1) AB + DC = AB.DC, 



(2) AB-fDC = AD + BG, 

 possibly passing through the stage 



AB. DC-AD + BC. 

 As an example of such a change, we have 



SnCl 4 + 5H 2 S = SnCl 4 . 5H 2 S, 

 SnCL 5H 9 S - SnS 2 + 4HC1 + 3H 2 S : 



* Phil. Trans. 1884. 



\ Journ. Chem. Soc. li. p. 803. 



|| Phil. Trans. 1888, "A." 



t Journ. Chem. Soc. 188G, p. 94. 

 § Wied. Ann. xxxii. p. 884. 



