" Inactive " Condition of Solids. 139 



Exp. 2. A glass rod and a platinum spatula that had been 

 long exposed to the air were dipped first into A, then into B. 

 Gas-bubbles were abundantly liberated from the surface of both. 

 They were dipped into spirits of wine, rinsed in water, and then 

 placed in A and B. Not a bubble of gas appeared on either 

 surface except above the points at which the bodies had been 

 made chemically clean ; and there plenty of gas-bubbles appeared. 

 Indeed it was accurately determined by the formation of those 

 bubbles how far the rods had been dipped into the spirit. 



Now in these cases, where the surface is made chemically clean, 

 the attraction of adhesion between the liquid and the surface is 

 perfect. The clean surface is completely wetted, and there is no 

 liberation of gas*. But let the surface be not chemically clean 

 (and it readily becomes so by even a few minutes' exposure to the 

 air, or by handling, &c), then the adhesion is imperfect ; the 

 liquid does not wet the surface completely, and the gas, yielding 

 to the superior attraction of the solid, adheres to it. That is, 

 where there is but small adhesion between the liquid and the 

 solid, there may be strong adhesion between the gas and the 

 solid ; and hence it is that bodies not chemically clean are favour- 

 able for the liberation of gases from their solution sf. 



But it is said that the condition of the surface as to roughness 

 or smoothness has much to do with the action of the solid in 

 liberating gas. I do not find such to be the case, provided the 

 condition of chemical purity be attended to. 



Exp. 3. A rat's-tail file, that liberated gas abundantly on 

 being immersed in soda-water, was washed in spirit and rinsed in 

 water ; but it still liberated gas. It was then held in dilute sul- 

 phuric acid for about a minute until there was a decided smell of 

 hydrogen ; it still disengaged gas. It was then put into spirit 

 and kept there during some hours. When immersed in fresh 

 soda-water, not a single bubble of gas appeared on the surface of 

 the file. 



Exp. 4. The file was dried with a duster and drawn through 

 the moist hand, when on being placed in soda-water it libe- 

 rated bubbles of gas abundantly. It was now no longer che- 

 mically clean. 



Exp. 5. Dry iron-filings gently placed in soda-water liberated 

 an abundance of gas, and some of the filings were raised from 

 the bottom to the surface by gas-buoys. 



* 1 find spirits of wine more efficacious in cleaning the surfaces than 

 sulphuric or nitric acid, ammonia, or caustic potash solution. 



t A bottle of nitric acid that had become of a dark orange colour by ex- 

 posure to the light, disengaged gas freely from the surface of a platinum 

 spatula put into it. When the spatula was made chemically clean there 

 was scarcely any discharge of gas. 



