478 Jf. Carey Lea — Allotropic Forms of Silver. 



Newbury concludes to be a suspension of finely divided silver. 

 Muthmann* after a careful examination of Pautenberg's pro- 

 ducts concludes that that chemist was wholly in error in assert- 

 ing the formation of compounds of chromic, molybdic and 

 tungstic acids with silver hemioxide. He next studies the red 

 liquid obtained by Wohler's process and comes to the same 

 conclusion as Newbury, that it consists of finely divided silver 

 suspended in water. 



I shall not dispute the correctness of this opinion in the case 

 of the liquid examined by these two chemists. At the same 

 time I cannot accept the tests of solution employed by Muth- 

 mann. That a substance will not pass through a dialyser shows 

 that it is colloidal and is no proof whatever that it is not in 

 solution. Animal charcoal takes up many substances from true 

 solutions. Decolorization by animal charcoal is no proof what- 

 ever that the color removed was not in true solution. By 

 freezing, the molecular condition of a substance may be changed. 

 Muthmann found that when the red liquid was mixed with 

 gum water and precipitated by alcohol, the precipitated gum 

 carried down with it the red substance, thence deducing that 

 it was only in suspension. This conclusion is scarcely justified. 

 A solution of litmus was mixed with gum water and precipi- 

 tated with alcohol : the mass of the litmus went down with the 

 gum, a trace only appeared in the filtrate. With Hoffmann's 

 violet, the same result. Yet no one, 1 think, will assert that 

 these two substances do not make true solutions in water. 

 Even however, if these arguments could be admitted they 

 would not apply to the solutions presently to be described, 

 which can be proved by optical means to be true solutions. I 

 propose presently to show that silver may exist in a perfectly 

 soluble form, dissolving easily and abundantly in water. Start- 

 ing from this, it may show all degrees of solubility down to 

 absolute insolubility, still however, existing in an allotropic 

 form and quite distinct from normal or ordinary silver. The 

 solutions formed are as perfect as those of any other soluble 

 substance. 



Wohler's process was next repeated by G. H. Bailey and G. 

 J. Foster, who came to the conclusion that no citrate of hemi- 

 oxide was formed, and that Wohler's results must be rejected. 



Yon der Pf ordtenf endeavored to obtain hemi-compounds of 

 silver by acting on the nitrate with an alkaline solution of 

 sodium tartrate, and also with phosphorous acid. His deter- 

 minations were made volumetrically, based on an opinion that 

 a permanganate solution acidified with sulphuric acid would 

 dissolve silver hemioxide, but not metallic silver. Previously 

 to receiving his paper I had found that sulphuric acid, even 



*Bericht der D. Ch. Ges., xx, 983. f Ibid., xx, 1458. 



