ACTION OF THE HALOGENS^ ETC. 169 



somewhat diluted sulphuric acid which remains on the crystals. The 

 analysis of this variety gives however good results because the extra 

 water which is present compensates the extra amount of sulphuric 

 acid. When the red variety is dried in the desiccator, the water of 

 crystallization is removed, not however that which is present on 

 account of the mechanically adhering acid. A too high amount of 

 sulphuric acid is therefore found, always about .6%. This assump- 

 tion, that mechanically adhering diluted sulphuric acid influences the 

 analysis, was confirmed by the following water determinations, in 

 which it was found that the yellow variety really contained from .1% 

 to .2% of water. 



The determinations were made from samples from three differ- 

 ent crystallizations. The following amounts of substance were 

 heated at 110° to constant weight: 



.1491 grms. lost .0106 grms.=7.11%. 

 .2417 " •' .0201 " =8.31%. 

 .1841 " " .0139 " =7.55%. 

 .2108 grms. lost .0028 grms.=1.18%. 

 .1717 " " .0034 " =1.98%. 

 .2369 " " .0030 " =1.27%. 



Difference between the corresponding 

 red and yellow modification =amount 

 Computed: of water found. 



2H,O = 6.20%. «— a'=5.93%. 



6— 5'=6.33%. 

 ,,'_c'=6.27%. 

 From this it seems most probable that the red modification con- 

 tains two molecules of water of crystallization, while the yellow in 

 the pure state would be anhydrous. 



Hydrochloric Acid Salt. 



The base dissolves with difliculty in concentrated, easily in 

 dilute, hydrochloric acid. From this solution yellow crystals of the 

 HCl salt separate out. It is better however to dissolve the base in 



