Chemical Properties of Stannic Chloride. 389 



sulphide was a function of the temperature-change. Was its 

 formation induced by the elevation of temperature ? It was 

 noticed that, on warming up the product obtained by passing 

 the dry gas into the liquid, the white crystals dissolved and 

 the liquid became yellow ; there was thus a probability that 

 these white crystals would prove the key to the change. 

 Some of the crystals were separated and heated ; they then 

 evolved sulphuretted hydrogen, hydrochloric acid, and left a 

 residue of stannic sulphide. But it still remained to examine 

 whether the unheated saturated stannic chloride contained 

 any stannic sulphide. This point was determined by evapo- 

 rating the saturated liquid to dryness without heating it, an 

 operation which could be effected by taking advantage of the 

 volatility of the tetrachloride. A current of thoroughly dried 

 air was steadily driven into the saturated tetrachloride : fumes 

 of the tetrachloride mixed with sulphuretted hydrogen were 

 evolved ; but in the end, when all the liquid had disappeared, 

 it was found that not a trace of stannic sulphide had been 

 formed, and that in its place was a residue of the white crys- 

 talline solid. Therefore, then, dry sulphuretted hydrogen 

 may be passed into the tetrachloride, and, if the temperature 

 be not raised, not a trace of stannic sulphide is formed : by 

 far the greater part there is no combination, to the smaller 

 extent these crystals are formed. The transformation which 

 these crystals undergo when heated fully explains the forma- 

 tion of the stannic sulphide observed by Dumas. The com- 

 position of these crystals was determined. A small tube was 

 weighed and about ten grams of the tetrachloride were placed 

 in it, and saturated with dry sulphuretted hydrogen ; the 

 liquid was then evaporated to dryness by a current of dry air. 

 In this way, in two experiments, were obtained in the tube, 



(1) 1*15 gram of the compound SnCl 4 , wH 2 S. 



(2) -926 



The tubes were then carefully heated by a spirit-lamp. The 

 solid melted and evolved sulphuretted hydrogen ; and next, 

 as the heating was continued, hydrochloric acid, and a residue 

 of stannic sulphide to the amounts respectively, 



(1) *48 gram, 



(2) -365 „ 



which numbers correspond closely to the value n = 5. These 

 white crystals, which are the sole product of the action of 

 dry sulphuretted hydrogen on stannic chloride, are thus 

 SnCl 4 . 5H 2 S, analogous to SnCl 4 . 5H 2 0. 



The reaction which occurs on heating is thus : — 

 8n01 4 . 5H 2 S^ SnS 2 + 4HC1 + 3H 2 S. 



