The Action of Metals^ &c.y on India-rubber. 275 



proofed cloth, as when they are also present. The following^ 

 table gives the proportions of oily and greasy matters 

 present in the two samples of dyed cloth above-mentioned^ 

 and also the percentages of copper contained in them, 

 and also the proportion of copper contained in two cloths, 

 marked " E " and " C," which had been proofed, and become 

 hard within a few weeks or months : — 



Per cent. 

 Oily and Copper Oxide. 

 Greasy Matter. (CuO). 



Black Cloth ("I") 3-38 0-29 



*Decomposed Proofed Cloth, \ 



said to be same as above >... 0*12 



after proofing ("E") ) 



Black Cloth ("M") 3-14 1-30 



*Decomposed Proofed Cloth, \ 



said to be same as above V... 0*33 



after proofing ("C") ) 



Within the last few years a bright blueish black has been 

 produced by means of copper salt with logwood, or more 

 commonly by dyeing, first with logwood, using iron salts as 

 a mordant, and finishing the dyeing with the use of a 

 copper salt as a mordant, and it will be found that if cloth 

 so dyed be proofed, the rubber will rapidly perish. It is 

 remarkable that cloths proofed with a mixture of india- 

 rubber containing a large quantity of " india-rubber sub- 

 stitute" (vulcanized oil) are not so easily affected by copper 

 salts as those proofed with pure india-rubber. A curious 

 piece of evidence as to the action of copper on rubber came 

 into the hands of one of us, after proofing the above- 

 mentioned pieces which had been divided into 3 parts as 

 above described and obtaining the results just given. A 

 chemist placed in our hands two pieces of the same black 



* These pieces were prepared by the same manufacturer, and said by the 

 proofer to be from the same lots respectively as the unproofed cloths marked 

 "I" and "M." 



