690 REPORT— 1892. 



in this cell fully into electrical energy, the metal being solid, there must be a. 

 difference of both the energies if the same metal is in the liquid state, and vice 

 versa. It is therefore proved that there must exist cells whose chemical and 

 electrical energies are not equal. 



4. Note on Exact Weighing. By Dr. J. Gibson. 



5. Analysis of Manganese Nodules. By Dr. J. Gibson. 



6. On the Iodides of Sulphur. 

 By Professor Herbert McLeod, F.B.S. 



An iodide of sulphur, Slg, isomorphous with iodine was prepared by Landolt and 

 measured crystallographically by vom Rath (Pogg. ' Aunalen,' ex. 116). It was 

 made by allowing a solution of iodine and sulphur in carbonic disulphide to evapo- 

 rate spontaneously. As the existence of this compound has been adduced as a 

 proof of the hexad character of sulphur, it seemed advisable to investigate its 

 properties. 



Some of the substance was prepared by the process mentioned, and in order to 

 separate it from any admixture of iodine it was placed in a tube which was after- 

 wards exhausted by the Sprengel pump and sealed. One end of tlie tube was then 

 surrounded by muslin, kept wet with water by means of a piece of cotton-wick; 

 iodine volatilised, at first rapidly, but afterwards more slowly. After the lapse of 

 three months a residue was left at the end of the tube, which, on analysis, was 

 found to contain 98'5 per cent, of sulphur. 



Another quantity was dissolved in carbonic disulphide and the solution allowed 

 to evaporate ; as crystals were formed the liquid was poured off and the crystals 

 washed with carbonic disulphide. In this manner five crops of crystals were 

 obtained, none of which contained more than -5 per cent, of sidphur ; the residue 

 left on allowing the mother liquor to evaporate contained 56 per cent, of sulphur. 



The iodine is entirely removed from the substance by digesting it in a solution 

 of potassic iodide. 



AVhen some of the powdered substance is exposed to the air in a shallow layer 

 the iodine all volatUises, leaving a residue of sulphur. 



"When acted on by a solution of sodic hydrate a residue of sulphur is left, and 

 the solution gives very little precipitate with baric chloride after acidifying with 

 hydrochloric acid. 



The properties of the substance seem to indicate that it is a mechanical mixture 

 of iodine and sulphur, and not a chemical compound. 



Some experiments were then made with the iodide of sulphur, SoL, described 

 by Guthrie. This was prepared by mixing chloride of sulphur, So01o,*with ethylic 

 iodide and allowing the mixture to remain in a sealed tube for four" days. Black 

 crystals were then found in the tube. On opening the latter a large quantity of 

 the vapour of ethylic iodide escaped. The crystals were removed from the tube 

 and powdered. On heating a portion in a test tube it fused at a temperature a little 

 above the boiling point of water. 



Some of the substance in vacuo gave oflF iodine, leaving a light-coloured residue. 



Some of the substance dissolved in sulphide of carbon was crystallised fraction- 

 ally : the first crop contained -38 per cent, of sulphur ; the second, SI ; the third, 

 1-07; and the fourth, 34-78. On allowing the mother liquor to evaporate the residue 

 contained 76'32 per cent, of sulphur. 



When acted on by sodic hydrate the iodine is removed and all the sulphur 

 remains behind, the solution giving no precipitate with baric chloride after adding 

 hydrochloric acid. It is usually stated in text-books that the compound undergoes 

 a decomposition similar to that of chloride of sulphur, forming an iodide and a 

 sulphite or thiosulphate with separation of sulphur. 



