British Association for the Advancement of Science. 25 
with any probability, be predicated of black cast iron got by the 
rapid cooling of the white variety, as suggested by Prof. Johns- 
ton.—Dr. 'Thomson stated, that cinder is a mixture of silicates 
of iron ; and subsequently expresbiid 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 
jence. 
The 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. 
which demonstrate the corrosion of lead by pure water, though 
saline water does not dissolve it. (This fact was first noticed by 
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 copper. 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, 
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 bias 
been acted upon; that in the second has been still more exten- 
sively corroded ; but that in the third continues perfectly bright 
Vou. XXXIV.—No. 1. 4 
