364 MR. HENRY ON THE COMPOUNDS OF TIN AND IODINE. 



substance could not be the neutral compound, for the 210 grs. of iodine would require 

 98 grs. of tin to form the protiodide instead of only 55 grs. 



The mass was therefore heated again in a Florence flask well-corked, with 45 grs. 

 of tin in very fine powder, to rephice the button removed from it, in order to ascertain 

 whether the neutral compound could be procured by digesting this substance with 

 the metal in a state more favourable to combination. The mass readily fused without 

 any further action on the tin ; but an orange-red sublimate was formed, condensing 

 on the sides of the flask in brilliant acicular crystals. As the mass in the flask dimi- 

 nished in quantity, it became less fusible, until at length it required a degree of heat 

 little short of dull redness to produce that effect, and then it ceased to giv^e off" 

 vapour. The flask was now allowed to cool ; when cold, it was cut, and the fused 

 residue removed, which was found to weigh 86*5 grs. after the separation of 37*5 grs. 

 of tin still uncombined. 



This substance was of a deep red colour and crystalline texture, affbrding a powder 

 of a bright red colour similar to that of minium ; 50 parts of it were treated with 

 strong nitric acid, which acted violently upon it, expelling iodine and leaving peroxide 

 of tin, which weighed after ignition 22*1 patts = 17-38 metallic tin =34-76 per cent. ; 

 a compound of one equivalent of tin = 59, and one of iodine = 126, would give 31-89 

 per cent. This excess in the quantity of tin arose from the heat employed in sepa- 

 rating the two compounds, producing a portion of oxide by the decomposition of the 

 protosalt, as will be seen further on. To ascertain the composition of the sublimate, 

 50 parts of it were decomposed by nitric acid, and gave 122 parts of peroxide 

 = 9597 metal = 19-19 per cent. 



100 parts, treated with a solution of pure carbonate of potash in slight excess, were 

 decomposed, carbonic acid being evolved and peroxide of tin precipitated ; the iodide 

 of potassium produced was separated by alcohol, and after dilution with water, was 

 treated with nitrate of silver; the precipitate dried and fused weighed 148-5=79-99 

 iodine. This gives 



Theory. Experiment. 



2 Iodine =252 81 79-99 



1 Tin . = 59 19 19-19 



311 100 99-18 



It was therefore a biniodidc. 



In the next experiment, I took one atoni of each substance, viz. 59 grs. of tin and 

 126 grs. of iodine. The action was violent as before ; there were 16 grs. of tin un- 

 combined, and after the sublimation of the biniodide, the fused protosalt weighed 

 66 grs. ; this was exposed to the air as little as possible during the process of subli- 

 mation, which being performed in a retort, less oxide was formed in consequence. 



50 parts gave 21*1 peroxide of tin =33*2 per cent, metal. In order to ascertain 

 the action of heat upon the protiodide of tin, I prepared some by precipitating a 

 warm concentrated solution of recently prepared protochloride of tin, by a strong 

 solution of iodide of potassium, in slight excess ; the salt formed on cooling in beau- 



