272 Mr. Wm. Thomson and Mr. F. Lewis on 



one marked 7th May, 1875, which was cold-vulcanized 

 with chloride of sulphur dissolved in bisulphide of carbon. 



We carefully tested the whole of these for copper, and 

 found that all those which were quite sound were perfectly 

 free from it, whilst the sample which had become hard con- 

 tained a -trace of that metal. It appeared, therefore, that 

 this trace was sufficient to bring about the complete 

 destruction of the rubber after a number of years. 



It may be well to give, as follow, the results of a series 

 of experiments and analyses of some cloths, the rubber 

 proofing on which was found to be destroyed within a few 

 weeks or months after they were proofed. We pasted 

 together, end to end, 19 samples of cloth, taken pro- 

 miscuously, in one long line, and had the whole of them cut 

 along the line into five equal parts. Each line of samples 

 was then covered with a continuous sheet of different india- 

 rubber mixtures, and one with pure Para rubber. Strips of 

 each series were cut along the whole line, and then were 

 looped and fixed so as to hang from stretched threads in 

 the incubator kept constantly at a temperature of 150° Fah. 

 They were examined from time to time, but, finally, after 

 25 days, they were removed, and their condition noted ; and, 

 simultaneously, the analyses of unproofed pieces of the same 

 cloths were made to find whether they contained copper, 

 and the quantity of copper was estimated in some of them ; 

 the quantities of oily or greasy matters present were also 

 estimated. The following table gives the results of the 

 observations and analyses, and shows that the rubber 

 remained good in all the samples of cloth which were 

 free from copper, whilst it was more or less seriously 

 damaged in all the samples which contained copper, and, 

 still further, the damage sustained was, as nearly as could 

 be observed, in direct proportion to the quantity of copper 

 present : — 



