486 M. Carey Lea — Allotropic Forms of Silver. 



combination with it, the remaining 2 or 3 per cent fully 

 accounted for by ferric oxide and citric acid determined as 

 present as accidental impurity ; the substance itself readily 

 amalgamating with mercury by simple friction, nevertheless 

 abundantly soluble in water. If I had been able to find any 

 other explanation for these facts without admitting the solu- 

 bility of silver, I should have adopted it. But none presented 

 itself. 



Whether in solution it exists as a hydrate, that is, in more 

 intimate combination with one or more equivalents of water, 

 cannot be said with entire certainty ; but the easy amalgama- 

 tion with mercury seems hardly to favor that view. No means 

 could be found for settling the question absolutely. Certainly 

 at 100° C. all water is expelled, but this is of course not an 

 argument. All the water is not expelled by indefinite expo- 

 sure to a vacuum over sulphuric acid. But the proportion left 

 is very small. 



The material examined was in all cases as nearly as possible 

 the same as that originally precipitated, but absolute identity 

 could not be obtained. The purification absolutely necessary 

 effects some change. This is shown by the color. The freshly 

 precipitated material dissolves to a blood red liquid, by great 

 dilution yellowish red. The purified substance gives a darker 

 red solution, which with dilution remains still red. Of the 

 nature of the substances in the condition in which they were 

 analyzed, I can speak with some positiveness, and these include 

 a substance soluble in water and nevertheless appearing to be 

 nearly pure silver. 



The constitution of the lilac blue substance at the moment 

 of formation and whilst still under its mother water is a matter 

 of more difficulty ; it could not be said with certainty that it 

 was not in some way altered in the purification. Much time 

 and labor were spent in endeavoring to settle this point, with- 

 out entirely satisfactory results, and I am at present engaged 

 in the search for a better method. 



When this blue soluble substance, purified either by washing 

 very moderately by ammonium nitrate, or by washing with 

 pure water, using those portions which remain undissolved 

 after most has been carried through the filter, is brushed over 

 paper and dries rapidly, it exhibits a very beautiful succession 

 of colors. At the moment of applying it appears blood red ; 

 when half dry it has a splendid blue color with a lustrous 

 metallic reflection ; when quite dry this metallic effect disap- 

 pears and the color is mat blue. Examined with a polarizer 

 it shows the same characters as to two reflected beams of light 

 polarized in planes perpendicular to each other that are 

 described further on under B. 



