374 Miscellaneous Intelligence. 



Dr. Prout admits the principle which M. VauqueHii claims the 

 discovery of, and attributes his want of success in obtaining 

 purpuric acid, to his having used impure lithic acid. Dr. 

 Prout always used pure lithic acid, obtained from the excre- 

 ments of the serpent exhibited as a boa constrictor. Perhaps 

 the observations published by M. Brugnatelli, of which an ac- 

 count is given at page 370, will assist M. Vauquelin in getting 

 over this difficulty. 



7. 071 the Decomposition of Chloride of Silver, by Hydrogen, and 

 by Zinc, by M, Faraday, Chemical Assistant, Sfc. — M. Arfwedson 

 some time ago communicated to me a mode of reducing chloride 

 ofsilver, by hydrogen (see Vol. 5, page 360.) 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 

 nascent state. But lately resuming the experiment, with the 

 intention of ascertaining why the nascent state was more favour- 

 able for the combination of the elements, than that of develope- 

 ment, 1 found reason to suppose that the hydrogen was not at 

 all concerned in liberating the chlorine from the silver. 



When zinc is thrown into chloride of silver, diffused through 

 dilute sulphuric or muriatic acid, hydrogen is liberated, and the 

 chloride suffers decomposition. But the same effect takes place 

 if zinc be thrown into chloride of silver, diffused through pure 

 water, so that the hydrogen which escapes in the state of gas, 

 cannot, in its nascent state, have been the decomposing agent. 

 It may however be supposed, that water is decomposed even 

 when no acid is present, and that thus hydrogen is still the 

 agent. But I find that zinc decomposes chloride of silver, even 

 more rapidly when unembarrassed by water, than when water 

 is present. Thus, if a little fused chloride of silver, and a 

 Small portion of zinc, be heated in a glass tube, a violent 

 action takes place ; chloride of zinc is formed, and silver libe- 

 rated, and the heat rises so high as generally to fuse the silver; 

 or if dry chloride of silver in powder be triturated in a mortar 



