SOO Dr MacCullocli on Black Lead from Cast-Iron. 
These pieces of iron were cast cones, perforated with holes, 
and about an inch thick, being used as strainers, to prevent 
foreign substances from getting into the pipes. They had been 
immersed in the porter for many years, — no one knew how 
many. On examining them, they appeared entire and un- 
changed ; but some of them, instead of being iron, were en- 
tirely of black lead ; and, in others, there was a thick coat of 
that substance on each side, a little iron only remaining in the 
middle. 
As this was then a new phenomenon in chemistry, 1 was in- 
duced to repeat the experiment in the laboratory, and it was 
attended with the same results, after some failures. An acci- 
dent, however, occurring about this time, shewed me that the 
fact was not so new as I had imagined, and I therefore took no 
notice of it in public. Since that it has been observed by many 
persons, who all probably imagined, with as good reason, that 
they had made the same discovery. As many of these accounts 
have appeared in your own Journal, I need not refer to them 
more particularly. 
The circumstance to which I allude was the following, which 
I happened to meet with in one of my journeys in the Western 
Islands. 
After Captain Roe had invented the diving-bell, he joined 
Sir Archibald Grant, a great speculator of that day in coal- 
mines and other matters, in an attempt to weigh the Florida, 
one of the Spanish Armada, which had foundered off the coast 
of Mull, near the entrance of Tobermory harbour ; she having 
been taken by the natives, assisted by some treachery on the 
part of the crew, which is said to have hung up the Captain at 
the yard-arm. There her timbers are still lying. 
This attempt, which took place in 1740, was unsuccessful, as 
far as related to the ship ; but some guns both of brass and 
iron were brought up. The former, whether they belonged to 
the Spanish vessel or not, had the mark of an English founder, 
R. and J. Phillips, 1584, with a crown and E. R. on them. 
The iron guns were deeply corroded, and on scraping them, it 
was said that they were found^so hot that they could not be 
touched, and that they did not become cool till they had been 
two or three hours exposed to the air. 
