on the Action of Water and Air on Lead. 85 



and the combination immersed in a phial of distilled water as 

 before. The next day, the white crystalline substance had 

 formed on the lead, and some rust on the head of the nail: 

 the point in contact with the lead remained bright many days. 

 Another nail, placed in a similar phial of distilled water, for the 

 sake of comparison, was covered by brown hydrated oxide in 

 three days. When the first arrangement was examined after 

 standing seven months, the nail next the lead was still partly 

 bright: the head was covered with rust, mixed with which the 

 grey laminar crystals of oxide of lead and the little dodeca- 

 hedral crystals were scattered over the surface both of the 

 lead and the iron. The water when tested by sulphuretted 

 hydrogen gave a deep brown tint. 



13. A slip of lead, which had the ordinary dull surface 

 which the metal acquires by exposure to the atmosphere, was 

 immersed in a phial of distilled water which had been agitated 

 with air, as in the previous experiments : the water was tested 

 at the end of a week by sulphuretted hydrogen, but gave no 

 indication of holding any lead in solution. 



On the white \flaky Crystals. 



14. Before I consider the nature of this substance, I should 

 observe, that when I made my first experiments on the sub- 

 ject, I was not acquainted with the researches of Dr. Christi- 

 son, contained in his Treatise on Poisons, p. 458 et seq., 

 2nd edit., but from my own (5.), I did not doubt that De 

 Morveau was right in concluding that the substance in ques- 

 tion was a hydrate. Dr. Christison, however, maintains as 

 the result of his experiments that both the white crystals, 

 whose external character he describes much as I have done, 

 and the lead held in solution by the distilled water, are in 

 the state of carbonate. Most, then, of the experiments that 

 follow were made with the knowledge of Dr.Christison's pre- 

 vious researches, and some with the particular object of deter- 

 mining between G. de Morveau's and my own first opinions 

 on the one hand, and Dr. Christison's results on the other. 



15. The substances were obtained as related (8.); the white 

 substance collected and dried in vacuo with sulphuric acid: 

 when dry it effervesced very slightly with a dilute acid. A por- 

 tion weighing 2*67 grains was introduced into a bent tube of 

 green glass closed at one end ; the open end of this was fitted in- 

 to another tube, both being provided with corks and previously 

 counterpoised : the substance was then heated red in the re- 

 tort tube, and some water condensed in the receiver tube ; the 

 tubes were then corked, and weighed when cold : the retort 



