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



being left in its original condition, one havingnpthe oily^ 

 and greasy matters removed, and the third having both 

 oily and greasy matters and copper removed ; these were 

 again joined in a line to a 'piece of grey cloth in its original 

 condition, and to a piece of the same from which the 

 oily and greasy matters were removed. It was, of course, 

 unnecessary to use a third piece of this cloth, as it was 

 free from any trace of copper. The eight pieces thus 

 arranged in one line were divided along the line into two 

 parts ; one was covered with a continuous sheet of pure 

 Para india-rubber, the other piece was covered with a 

 rubber composition. Both were vulcanized by the cold 

 process, and afterwards arranged in loops, and hung in 

 an incubator at 140° Fah. for eight days. After that 

 time the rubber on both pieces of grey cloth and the two 

 pieces of black cloth, from which both grease and copper 

 had been removed (in both series), was found to be 

 perfectly sound, whilst the rubber on the two black cloths 

 in their original condition, and on the two from which the 

 oily and greasy matters had been removed, but in which 

 the copper remained, were completely destroyed, the effect 

 of the oil and grease in contact with the copper. (Some 

 of the copper contained in cloth is usually found in 

 solution in the oily or greasy matters also present). The 

 effect is to reduce the rubber to the condition of a soft 

 sticky substance, resembling grease in consistency, and to 

 this condition the proofing is soon brought when the oily 

 matter present in copper mordanted cloths exists in con- 

 siderable quantity. The mixture thus produced is often 

 absorbed into the fibre of the cloth, leaving it in a some- 

 what limp and sticky condition ; when, however, the oily 

 and greasy matters are removed, the rubber simply 

 becomes hard. It is curious, therefore, to find that the 

 presence of copper, even when oily and greasy matters are 

 absent, is almost as destructive to the rubber, on rubber 



