158 Wells, Wheeler and Penfield — Ccesium and 



the similarity of such formulae as CsCl . C1 3 I and CsCl.Cl 3 Au, 

 but since some of these gold salts have never been described and 

 as they show some interesting relations among themselves, our 

 results are deemed worthy of publication.* 



Th. Rosenbladt,f in an article on the solubility of the chlor- 

 aurates, states that the caesium and rubidium salts lose their 

 water of crystallization almost completely when dried over 

 sulphuric acid. He gives no statement of the amount of 

 water, but refers to his dissertation of 1872 which is inacces- 

 sible to us. He mentions, however, that the crystals of both 

 salts belong to the monoclinic system, so that it is probable 

 that the compounds he obtained were the ones that we have 

 found to be anhydrous. 



The compounds that have been prepared are CsAuCl 4 , 

 2CsAuCl 4 . H 2 0, CsAuBr 4 , Bb AuCl 4 and RbAuBr 4 . We have 

 attempted in each case to obtain bodies containing more caesium 

 and rubidium, but no evidence of their existence has been 

 found. 



An investigation of the corresponding iodine compounds 

 was also undertaken, but, on account of the instability of auric 

 iodide, we did not obtain any pure or well crystallized products. 



Preparation : — The salts are so insoluble that they form 

 precipitates when moderately concentrated solutions of the 

 component salts are mixed, and the products are readily recrys- 

 tallizecl from water or from the mother liquors. It is usually 

 immaterial whether the solutions are neutral or acid or whether 

 the gold or alkaline halide is in excess, but the salt 2CsAuCl 4 . 

 H 2 requires special conditions for its preparation, for it is 

 apparently formed only when a large excess of gold chloride 

 is present and when the solution does not contain much free 

 acid. We have used four atoms of gold to one of caesium in 

 making this salt, but it usually requires repeated trials under 

 these conditions before it is obtained free from the anhydrous 

 compound. The two salts are however so distinct in form that 

 there is no difficulty in distinguishing them. 



Properties: — The color of CsAuCl 4 and of 2CsAuCl 4 . H 2 

 is golden-yellow ; RbAuGl 4 is yellowish-red ; the two bromides 

 are black, but give a dark red powder. 



All the salts are. sparingly soluble in water, especially when 

 cold, and the caesium compounds are less soluble than the 

 rubidium. All of them are only slightly soluble in alcohol 

 and insoluble in ether. 



*The announcement by Professor Remsen (Am. Chetn. Jour., xiv, 89), that lie 

 and Mr. H. C. Jones proposed to examine the gold-rubidium halides, was not 

 made until after the work described in this article had been completed. 



f Berichte, xix, 2535. 



