96 Mr R. Adie's Experiments with Thermo- and 



when the large pole is on the hydrogen side, sparks may be obtained in 

 both gases ; then reverse the voltameter, and the hydrogen side only will 

 shew sparks. 



27. The cell, fig. 4, was used to carry on electrolysis under great pres- 

 sure, when it appeared that a high pressure from hydrogen could change 

 the action from one where gas was eliminated, to another where metal 

 was deposited in lieu of the hydrogen. This takes place with many of 

 the metals, but the account of an experiment with copper poles decom- 

 posing water acidulated with sulphuric acid, should sufficiently illustrate 

 this kind of action. 



The voltameter is hermetically sealed ; electrolysis begins with the 

 formation of the black oxide of copper at the positive pole, and bells of 

 hydrogen rise from the negative pole ; the gas eliminated, rapidly in- 

 creases the pressure in the voltameter ; a blue solution of the sulphate of 

 copper soon appears between the two poles ; hydrogen then gradually 

 ceases to rise, the last bubbles of gas adhere to the pole ; at this stage, 

 with the voltameter in the focus of a microscope, a brown film appears 

 to coat the gas-bells attached to the pole, which changes to be more and 

 more opaque, until the exterior surface of a beautiful sphere of copper ap- 

 pears in the field of the instrument. Naw nip off the point of the capillary 

 tube, so ab to remove the pressure in the voltameter ; immediately, the 

 original action recommences, viz., oxide of copper at the positive pole, 

 and hydrogen at the negative pole, and continues until the solution of the 

 sulphate of copper becomes strong enough to allow the precipitation of the 

 metal to go on under atmospheric pressure. Here the compressing force 

 merely effects a change quickly, which, under ordinary circumstances, 

 would have been brought about by time, so that with compounds of an 

 evanescent kind, this mode of manipulating may be useful. 



28. A number of decomposing cells, fig. 4, were prepared with a pair 

 of poles, of each of the undernoted metals, and filled with a saturated 

 solution of pure common salt ; to ascertain how many of them could be 

 oxidized at the positive, and deposited in a metallic form at the negative 

 pole, through this wide-spread solution. Deposits on the negative pole 

 appeared in leaf-like forms while using poles of silver, copper, tin, z-inc. 

 The last metal is difficult and uncertain ; in the majority of the experi- 

 ments, the cells burst before any zinc appeared. Deposits on the nega- 

 tive pole were obtained in a pulverulent form ; for antimony, palladium, 

 and platinum, black ; cobalt, dark brown ; gold, dark purple ; arsenic, 

 a flocculent dark brown ; mercury, whitish grey. The antimony and 

 platinum required a high pressure before their deposits appeared. Iron, 

 lead, bismuth, cadmium, and nickel poles, eliminated hydrogen until 

 they burst the strongest cells ; but of these five exceptions, three of them 

 can be transferred through another element of sea- water, iodide of potas- 

 sium or sodium : when this solution is substituted for common salt, lead 

 is obtained in beautiful leaves at the negative pole, bismuth and cadmium 

 as dark powders. In the 16 pairs of poles of different metals tried, there 

 are only two from which a metallic deposit on the negative pole cannot 



