388 Mr. W. Coldridge on the Electrical and 



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(h) " The product is a yellowish or reddish liquid heavier 

 than water." 



It was noted that no mention is made of the white crystal- 

 line compound. 



(c) " On heating the liquid, SnCl 4 is evolved and SnS 2 

 remains." 



This observation as to the residue of stannic sulphide was 

 verified, and beautiful specimens of the "mosaic gold" were 

 obtained. But it should be noted that the liquid has been 

 heated. 



The following experiments were then made : — 



(a) The fumes which are evolved on passing in dry hydro- 

 sulphuric acid smell strongly of the sulphuretted hydrogen 

 even when the gas was slowly delivered, and immediately 

 blacken moist lead-acetate paper : they are moreover acrid, 

 and distinctly smell of the tetrachloride rather than of hydro- 

 chloric acid. But to establish the presence of the tetrachloride 

 vapour, a test more reliable than the sense of smell was 

 required. The following was devised : — A glass rod with a 

 drop of water at the end was held in the fumes ; after a 

 minute, whilst the dry liquid below remained colourless and 

 clear, here in the drop of water stannic sulphide was deposited. 

 The fumes therefore contain the vapour of the tetrachloride 

 and sulphuretted hydrogen, which are caused to combine by 

 the action of the water. Thus, then, the statement that hydro- 

 chloric-acid gas is evolved, if it be in the least degree posi- 

 tively true, is fatally incomplete. 



(6) The liquid compound, the supposed stannic sulpho- 

 chloride, was next distilled. The warming was gently regu- 

 lated ; as the temperature rose gradually to 50°, 60°, 70°, 

 sulphuretted hydrogen was copiously evolved in such quantity 

 that the liquid assumed the appearance of boiling, whereas 

 distillation had not commenced. At 112° C, the boiling- 

 point of stannic chloride, a free distillation commenced, and 

 the greater portion of the tetrachloride was thus recovered. 

 Finally the temperature rose, a solid residue melted, and 

 stannic sulphide remained, though, from a gravitation expe- 

 riment, in less quantity than was required by the hypothetical 

 constitution " SnS 2 . 2SnCl 4 ." A veritable compound stannic 

 sulpho-chloride could not at low temperatures evolve sul- 

 phuretted hydrogen copiously and then distil at the ordinary 

 boiling-point of stannic chloride. 



(c) The presence of the residue of stannic sulphide proved 

 that, on passing dry hydrosulphuric-acid gas into the chloride 

 and then subsequently heating, some reaction occurred. But 

 the question remained as to how far this production of the 



