PROFESSOR CHRISTISON ON THE ACTION OF WATER UPON LEAD. 275 



with one equivalent of hydrated oxide of lead. The exact numbers by calculation, 

 supposing the oxide correct, are 21.035 oxide, 2.656 acid, and 0.540 water. The 

 slight deviation in my numerical results for the carbonic acid from the exact ato- 

 mic numbers, probably depends on some of the protoxide of lead having absorbed 

 oxygen from the atmospheric air passed through the tubes at the close, while heat 

 was applied to the oxide, so that some of it became red oxide of lead. 



This experiment was repeated with 27.965 grains, and the products were 



Oxide of lead, * . "' . . . 24.275 



Carbonic acid (6.33 cubic in.), '/' . ''."" 2.992 



Water, . . 0.650 



27.917 



These numbers, like the last, approach closely to the theory 3PbO 4. 2C0 2 + Aq, 

 the exact numbers, by calculation from the oxide, being 3.06 of carbonic, and 

 0.62 of water. 



In a third trial with 23.935 grains, the results were 



Oxide of lead, ..... 20.870 



Carbonic acid (5.285 cubic in.), . . . 2.497 



Water, . . . . . . 0.547 



23.914 



Theory applies here exactly so far as regards the water, but the acid is somewhat 

 deficient, the correct numbers, by calculation from the oxide, being 2.635 acid, 

 and 0.540 water. 



I have also examined the proportion of carbonic acid in other differently pre- 

 pared specimens, by wrapping the powder in filtering paper, and introducing this 

 into a jar filled with mercury and a little strong muriatic acid previously charged 

 with carbonic acid gas. The results have been conformable with those stated above. 

 When the water was freely exposed to the atmosphere, I have never found that 

 the proportions differed more than a small fraction from the theoretical numbers 

 just assigned. 



The substance in question is therefore a definite compound of two lead salts. 

 Other analogous examples have been for some time known to exist among the 

 oxides and salts of this metal. Though of a brilliant whiteness while in water, 

 it is rather gray when dry. It is permanent in the air ; for a specimen exposed 

 for many months gave the usual proportion of carbonic acid, when decomposed 

 with muriatic acid. When suspended in water and treated with a stream of car- 

 bonic acid, the water of the hydrated oxide is displaced, and a neutral carbonate 

 is formed, which is more dense, and of a pure white colour when dry. 



On first ascertaining the nature of this substance, I imagined it was a new 



