1820.] Chloride of Silver, Hydrogen, and Zinc. 31 



alone, it is not, in the first case, of sufficient quantity, and in 

 the second, it would be diminished by dilution. 



It is probable that if the tints produced be compared exactly 

 with those occasioned by alkalies, slight differences might be 

 perceived among some of them ; or that if the properties of 

 the altered colouring matter were examined, they would be 

 found different with the different substances, as M. Desfosses 

 has shown with regard to boracic acid and other acids ; but my 

 object has not been to trace these changes as far as possible, 

 but merely to show their general appearance ; to guard against 

 any deceptive conclusion with respect to solutions tested by 

 turmeric ; and to call attention to the distinguishing characters 

 of acids and alkalies. 



Action of Salts on Turmeric Paper*. 



AMONG the salts not alkaline, which have the power of affecting 

 turmeric paper like alkalies (see pp. 29, 30), those of uranium 

 are perhaps most powerful. The muriate, sulphate and acetate 

 affect turmeric paper strongly even when considerably diluted; 

 but the nitrate is the most powerful. A strong solution scarcely 

 seems to have its power diminished by dilution with ten or 

 twelve times its weight of water, and even when the solution 

 contains only ^^th of dry nitrate of uranium, it sensibly browns 

 turmeric paper. 



The muriate of zirconia also possesses this same property to 

 a considerable degree. 



On the Decomposition of Chloride of Silver by Hydrogen 



and by Zinc }. 



M. ARFVEDSON some time ago communicated to me a mode of 

 reducing chloride of silver by hydrogen J. In a few experi- 

 ments made some time since, in consequence of this communi- 

 cation, I found myself unable to decompose the chloride by a 

 stream of pure hydrogen gas, or by allowing an atmosphere of 

 the gas to remain for a long time in contact with it ; I supposed, 

 therefore, that the effect was produced by the hydrogen in its 



* Quarterly Journal of Science, xiv. 234. 

 t Ibid. viii. 374. t Ibid. v. 360. 



