ON ELECTEOLYSIS IN ITS PHYSICAL AND CHEMICAL BEARINGS. 349 



Eolarisation after the current had passed through, but so slight that it might have 

 een due to impurity. The conduction was almost entirely non-electrolytic. 



Copper Sulphide, CuS. — This compound also, whether fused and powdered or 

 obtained as a precipitate, conducts readily enough. When silver electrodes were 

 used no polarisation could be detected. With platinum electrodes very little. The 

 silver plates remained bright when the fused sulphide was employed ; with the 

 precipitated substance they were both marked. 



Irmi Sulphide. — Natural iron pyrites gave no polarisation or discolouration of 

 the silver electrodes. An artificially-prepared fused compound gave a little polari- 

 sation, but its composition varies. 



Bismuth Sulphide. — Conducts very little. No polarisation was obtained. 



Mercury Sulphide {cinnabar). — Same results. 



Potassium Sulphydrate. — Dried at a red heat, this was found to be a non-con- 

 ductor. The same appears to be true of the sulphides of calcium and barium. 



It appeared, tlierefore, that solid sulphides divide themselves into two classes : 

 those which are electrolysed, and those which conduct with little or no decomposi- 

 tion. Now it happens that the two sulphides which are easily electrolysed — namely, 

 the silver and cuprous sulphides, are of analogous constitution, AgoS and Ou.^S, 

 and differ in that respect from the others. It occurred to us that the thallium 

 sulphide T1.,S might be like them. Mr. Crookes kindly gave us some small bars of 

 this compound, saying at the same time that he had found its power of conducting 

 electricity to be very rapidly augmented on heating. We found that it rapidly in- 

 creased in conductivity to about 105°, about which temperature it also softened, 

 and the conduction was accompanied by considerable electrolysis. We dissolved 

 up this specimen and estimated the thallium and sulphur. The results showed 

 that it contained much more sulphur than the compound Tl^S. It was probably a 

 mixture of that body with the compound TljSj, which is said to be soft even at a 

 summer temperature. 



We therefore prepared a specimen of the thallious sulphide T1„S ourselves, and, 

 after carefully drying it at 125° in a current of carbonic acid, found it on analysis 

 to be nearly pure T1.,S. This compound was not melted even at a temperature of 

 290°-300° C. It shows a small conduction at ordinary temperatures, and up to 

 100°, after which it increases slowly to about 170°. Beyond this the increase is 

 fmore rapid. 



Throughout the greater part of this range of temperature — that is, from 50° 

 upwards — there was evidence of polarisation, the value of which increased very 

 rapidly as the temperature rose from 100° to 130°. Measurements were made by 

 the potentiometer method, the highest value obtained being very nearly 0'3 volt. 



The results, therefore, in this case agree with our anticipation that solid sul- 

 phides similar in constitution to the silver and cuprous sulphides are capable of 

 being electrolysed ; while solid sulphides of the type MS conduct with little or no 

 decomposition. 



On the Electrolysis of TJiallium Trisulphide. 

 By J. H. Gladstone, Ph.D., F.B.S., and W. Hibbeet, F.I.G. 



In a communication made to the Committee in the early part of this year we 

 gave the results of some experiments on the electrolysis of solid sulphides. It was 

 pointed out that the sidphides electrolysed up to that time — silver and cuprous 

 sulphides — were of analogous constitution, containing two atoms of metal to one of 

 sulphur. Led by this circumstance, we succeeded in getting electrolysis of another 

 similar compound — thallious sulphide, TLS. 



Some of our early experiments happened to be made with a compound contain- 

 ing more sulphur than that required by the formula T1.,S, and this suggested an 

 attempt to electrolyse the compound of thallium and sulphur which has the 

 formula TLSg. This compound is soft and plastic at the temperature of a warm 

 summer day, and might reasonably be expected to show electrolysis. 



We found some difficulty in preparing the compound by the method given — i.e., 

 by fusing thallium with excess of sulphur, and driving off the excess at a very high 



