British Association for the Advancement of Science. 25 



with any probability, be predicated of black cast iron got by the 

 rapid coohng of the white variety, as suggested by Prof. Johns- 

 ton.— Dr. Thomson stated, that cinder is a mixture of sihcates 

 of iron ; and subsequently expressed his conviction, that the qual- 

 ity of iron, notwithstanding what had been alleged to the contra- 

 ry, is chiefly dependent on its composition, and that if phosphorus, 

 for example, or sulphur, were present, the metal could not be 

 good. The same gentleman, in conclusion, decried the doctrine, 

 which would place what was called the Rule of Thumb above 

 what he considered a much more valuable guide — the Rule of 

 Science. 



77ie action of Water upon Lead. — Mr. Pearsall brought under 

 consideration the action of water upon lead. He commenced by 

 a reference to the researches of Col. Yorke and Prof. Christison, 

 which demonstrate the corrosion of lead by pure water, though 

 saline water does not dissolve it. (This fact was first noticed by 

 Guyton Morveau.) The great object of his communication was 

 to show, that rain water collected in leaden cisterns will dissolve 

 the metal in considerable quantity, probably as hydrated oxide, 

 but that, if such water be passed through a filter, or agitated with 

 carbonaceous matter, it is altogether removed. This point he es- 

 tablished in the course of some investigations having a reference 

 to certain disastrous cases of poisoning which have occurred re- 

 cently at Hull. 



Mr. Mallet stated, that, according to his experience, lead alone 

 is corroded which contains c»pper. This opinion was combated 

 on the ground, that all the lead of commerce includes copper. 

 Col. Yorke also stated, on the other hand, that he had established 

 that perfectly pure lead is corroded by water when it contains air ; 

 that the calx is of a crystalline nature, and composed, according 

 to his experiments, of carbonate united to oxide of lead. A gen- 

 tleman, whose name we could not learn, stated, that the follow- 

 ing experiment was instituted some years ago, and is still in pro- 

 gress. Into three bottles, filled, the first with Thames water, the 

 second with distilled water containing air, and the third with dis- 

 tilled water deprived of air, three slips of lead were introduced, 

 and the bottles hermetically sealed. The lead in the first has 

 been acted upon ; that in the second has been still more exten- 

 sively corroded ; but that in the third continues perfectly bright 



Vol. XXXIV.— No. 1. 4 



