432 Blake — Composition of Bredig's Siloer Rydrosols.. 



metallic silver collected on it, from wliicli tlie yellowish clouds 

 were derived ; the anode at first gave rise to snow-white clouds 

 (silver hydroxide % ), but soon became coated with a brown-red 

 layer of silver peroxide, whereupon the white clouds ceased to 

 be evolved in appreciable amount. On one occasion, when the 

 anode was nearly touching one of the asbestos plugs, a bridge 

 of tlie snow-white material was formed between the anode and 

 the asbestos. When the current was broken this band soon 

 dissolved, leaving a skeleton of peroxide ; but the white band 

 re-formed when the circuit was closed again. The resulting 

 solution was strongly alkaline at first, but became neutral by 

 standing, doubtless because silver hydroxide was originally 

 present in the solution and was changed to the carbonate by 

 the carbon dioxide of the air. Part of the silver derived from 

 the yellowish clouds remained in suspension, forming a 

 hydrosol."^ When alcohol is substituted for the water no 

 action takes place without sparking and only the cathode is 

 eroded with sparking, forming a black silver alcosol, thus 

 strengthening the supposition that the erosion of the anode in 

 the presence of water when the spark is not passing is due to 

 oxidation. It would seem very likely, moreover, that the 

 anode would be similarly oxidized while the spark is passing, 

 not to mention the possibility that part of the finely-divided 

 silver torn off from the cathode might also be oxidized when it 

 is carried into the region of the anode. 



In Bredig's method of preparing silver hydrosols by spark- 

 ing between silver electrodes under water, the current is 

 frequently stopped on account of the rapid erosion of the 

 electrodes. During such intervals of stoppage the conditions 

 are the same as in the experiments of which a description has 

 just been given, excepting, possibly, the distance between the 

 electrodes. It seems certain, therefore, that in Bredig's 

 experiments silver compounds must have been formed, thus 

 accounting for the facts mentioned in the opening paragraph 

 of this note, and for the fact, noted by Mcintosh, f that the 

 electrical conductivity of the water is greatly increased by the 

 process of sparking. It would seem essential that these facts 

 should be taken into consideration in such extended investiga- 

 tions as the latter author has made on the catalytic properties 

 of the finely-divided silver contained in hydrosols prepared 

 according to Bredig's method, especially when working with 

 neutral or acid solutions. 



This inquiry was made at the suggestion of Prof. F. A. 

 Gooch, to whom my thanks are due. 



*Cf. Billitzer, Ber. Deutsch. chem. Ges., xxxv, 1929. 

 f Jour. Phys, Chem., vi, 15. 



