482 31. Carey Lea — Allotropic Forms of Silver. 



salts present : this much will dissolve the greater part but not 

 the whole, which is not necessary. A little of a saturated 

 solution of amnionic nitrate is to be added, just enough to effect 

 complete precipitation. 



As the material appears continually to change, the amount 

 of washing needed must depend upon the object in view. If 

 wanted for analysis, the washing must be repeated many times 

 until ferric salt ceases to come away, but no amount of washing 

 will entirely eliminate it. After seven or eight solutions in 

 pure water and as many precipitations, the material is to be 

 thrown on a filter, the liquid forced out as completely as pos- 

 sible with a pump and then the amnionic nitrate washed out 

 with 95 per cent alcohol until the filtrate leaves nothing on 

 evaporation. The substance at this point is still soluble in 

 water, though much less so thau at first. During the washing 

 the solubility slowly but steadily diminishes, a fact rendered 

 noticeable by less and less amnionic nitrate being needed to 

 precipitate it from its solution. 



Analysis. — The product after thorough washing as above 

 described with alcohol, was dried at ordinary temperatures or 

 a little above, and was then reduced to very fine powder and 

 washed again with water as long as anything dissolved. It 

 was then dried at 100° C. in water bath. Three silver deter- 

 minations were made. 



Al 97*31 per cent silver. 



A2 97-18 " 



B 97-21 " " 



Al and A2 were made with different portions of the same 

 material, JB with different material prepared in exactly the 

 same way. 



The substance therefore contained on an average 97*27 per 

 cent of silver. The nature of the residue would decide 

 whether the material was silver with a certain amount of 

 impurity firmly attached to it, or whether we had to do with 

 silver in chemical combination with other elements. 



The filtrate from the silver chloride in analysis A2 was 

 evaporated to dryness and was found to contain chiefly iron 

 and citric acid. The iron was thrown down as sulphide, redis- 

 solved in nitric acid, precipitated hot, washed with boiling 

 water and gave 0894:7. The residue therefore consisted of 

 ferric oxide and citric acid, probably in the form of ferric 

 citrate and attached so strongly that even the very careful and 

 prolonged washing given failed to remove them. Stronger 

 means would be required than could be used without altering 

 the condition of the substance. The conclusion therefore 

 seemed to be justified that the material consisted of uncom- 

 bined silver simply mixed with impurity. 



