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



small square sheets of the fine sheet rubber, adhering to paper, 

 and painted one with a solution containing lo per cent of 

 sulphate of copper. On weighing the amount applied to 

 the rubber it was found to be equivalent to 3 84 grains of 

 crystallised sulphate of copper per square foot. This solution 

 was then diluted with its own bulk of distilled water and a 

 second sheet painted with the diluted solution. This second 

 solution was again diluted with its own bulk of water, and 

 a third sheet painted with it, and so on. There were thus 

 prepared 6 pieces, containing the following quantities of 

 copper salt per square foot of thin sheet rubber : — 



Grains of Sulphate Equal to grains 

 of Copper of Copper Oxide 



(CuSO^sHaO). (CuO). 



Sheet {a) 3*840 1*218 



{p) I '920 o'6o9 



{c) 0-960 0-305 



(d) 0-480 0-153 



{e) 0-240 0-076 



(/) 0-120 0-038 



{g) , without copper. 



All these pieces were placed in the incubator at 140° 

 Fah. for 9 days, when it was found that the sample (/") 

 which contained the smallest quantity of copper, had 

 entirely lost its elasticity and become quite rotten, whilst 

 the piece (^), which contained no copper, was perfectly 

 sound ; on examining the others they were all found to 

 have entirely lost their elasticity, and to be hardened exactly 

 in proportion to the quantity of copper salt placed upon 

 their surfaces {a) being the hardest. It is, therefore, evident 

 that an extremely small quantity of a copper salt has a 

 highly injurious influence on rubber with which it comes into 



