Wells — Complex Chlorides containing Gold. 



323 



stood for a considerable time. It was finally f ound, how- 

 ever, that the dark color was due to the reducing action of 

 filter-paper and the formation of aurous chloride. The 

 solutions had been filtered frequently and extracts of the 

 filter-papers that had been used for drying the crystals 

 had been added to them. When a little nitric acid, left 

 after dissolving the gold, together with free hydrochloric 

 acid were present in the solutions the reduction was pre- 

 vented, but otherwise a single filtration of a hot solution 

 that had previously given an orange-red product caused 

 the formation of a very dark one. The following analyses 

 of some of these products were made : 



Cs 

 Hg 



Au 



ci . 



i 



Dark 

 brown, 

 trans- 

 parent 

 . 34.25 



24.99 



II 



Nearly 

 black, 

 trans- 

 parent 

 33.39 



III 



Black, 



opaque 



33.99 



26.19 25.07 



IV 



Black, 



opaque 



34.09 



25.15 



Black, 

 opaque 



14.81 

 24.32 

 26.48 



VI 



Black, 

 opaque 

 33.89 

 14.24 

 24.52 

 26.72 



Calculated for 

 Cs 4 HgAu 2 Cl 12 

 Orange- 

 red 

 34.23 

 12.93 

 25.42 

 27.42 



The first four analyses were made by the method of 

 heating in hydrogen, already mentioned, and on account 

 of the presence of aurous chloride reliable results for 

 mercury were not obtained. The determinations of mer- 

 cury and chlorine were made by weighing mercuric sul- 

 phide and silver chloride. 



The results show that the dark products differ but 

 slightly from the pure compound in composition. The 

 high percentages of mercury in the last two products indi- 

 cate that too large a proportion of mercuric chloride was 

 used in their preparation, resulting in the crystallization 

 with them of a little of the isomorphous double salt 

 CsHgCL. 



Efforts were made to prepare the pure black compound, 

 or to obtain some light upon its composition, by preparing 

 products from solutions that had been subjected to long, 

 hot digestion with filter-paper, but, on account of the 

 instability of aurous chloride, metallic gold was usually 

 precipitated during the digestion, and products of a con- 

 stant composition were not obtained in this way. After 

 the pure black triple salt had been prepared in a pure con- 

 dition by another method, to be described in the next sec- 

 tion of this paper, and its composition was known to cor- 



