BENEDICT. — DOUBLE SALTS OF ANTIMONY. 15 



crystals gave uo interference figure with the polariscope. This salt, 

 as the others, loses all its water of crystallization and antimonious 

 bromide in a desiccator over sulphuric acid, leaving a residue of mag- 

 nesic bromide. Analysis gave the following results : — 



a. 0.9131 gram of salt gave 0.2193 gram of antimonious sulphide. 



b. 1.1178 grams of salt gave 0.2128 gram of magnesic pyrophosphate. 



c. 0.5160 gram of salt gave 0.7044 gram of argentic bromide. 



d. 0.7013 gram of salt gave 0.1469 gram of water. 



Calculated for 

 SbBr3 . MgBr, . 8 HjO. Found. 



Antimony 17.40 17.15 



Magnesium 3.54 4.06 



Bromine 58.07 58.09 



Water 20.99 20.95 



100.00 100.25 



These three salts possess two important relations : — 



1. Entire uniformity of structure, i. e. one molecule of the alkaline 

 haloid combining with one molecule of the antimony haloid, and the 

 resulting compound crystallizing in each case with eight molecules of 

 water. 



2. Each salt completely dissociates at the ordinary temperatures in 

 a desiccator. 



The most strikins; feature of this research is the above mentioned 

 phenomenon. On attempting to estimate the water of crystallization 

 by desiccation, an irritating odor first indicated a decomposition which 

 was conclusively proven by the continual loss in weight. When con- 

 stancy in weight was obtained, the residue on treating with water 

 gave a hissing sound, and dissolved to a perfectly clear solution. This 

 solution, on acidifying with hydrochloric acid and adding a solution 

 of hydrogen sulphide, gave no precipitate, indicating an absence of 

 antimony. 



In the case of the salt SbCls . CaCl2 . 8 HgO, the per cent of residue 

 was 24.64, while the theoretical per cent of calcic cliloride in the salt 

 is 23.04. The excess would naturally be attributed to water which 

 the calcic chloride would not readily yield to the sulphuric acid in 

 the desiccator. The strong smell (volatilized antimony haloid) in the 

 desiccator was observed long before the theoretical amount of loss cal- 

 culated as water, i. e. 29.92^, had taken place. This showed that the 

 antimony haloid had escaped before all the water had left the mass. 



