On the Oxidation of Metals, particularly of Lead. 367 



means of an axis adjusted at its two extremities. Every one 

 knows how easy it is to turn round a machine of this kind 

 hy means of a water-mill. 



In order to procure a continual supply of fresh air in the 

 barrel, I contrived to introduce at various points in its cir- 

 cumference leaden tubes open at both their extremities, and 

 which almost met in the centre of the barrel in the form of 

 radii ; the other end of these tubes protruded a few inches 

 from the outside of the barrel, to which they were soldered 

 at their junction with it so closely as not to admit of any 

 water escaping. 



You will find in the box I have sent you a little bottle, 

 numbered 1., containing oxide of lead, prepared as above, 

 and which has never yet been taken out of the water. 



In No. 2. there are pieces of oxide dried in the air in a 

 glass capsule ; the brilliant white surface of it was exposed 

 to the air of a room during its desiccation, and the porous 

 and dirty white surface was that which was in contact with 

 the glass of the capsule. 



In No. 3. there is the same oxide hanging to the end of 

 the tube, and become yellow, then red, by simple exposure 

 to the light of the sun. The tube is scaled hermetically, 

 and filled partly with water and partly with atmospheric 

 air. 



InNo. 4. is thesarru.' oxide, hanging in a tube hermetically 

 scaled, also filled partly with water and partly with air, ex«- 

 posed for a very long time to the light on one side, but 

 coated on the other with a mixture of wax and lamp-black. 



No. 5. is a small bottle, containing oxide of lead agi- 

 tated with water and carbonic acid gas. 



If you find the present results worthy your attention, I 

 shall communicate to you the further progress of my expe- 

 riments. 



I have given the name of oxide to No. 1 . I think it is an 

 oxide, but it does not appear to be a common one : I would 

 have examined it with more attention, but it required more 

 time than I can at present spare. 



LXI. Ex- 



