17 
Ordinary Meeting, November 2nd, 1875. 
R. Angus Smith, Ph.D,, F.R.S., &c., Vice-President, in the 
Chair. 
Peter Spence, E.C.S., &c., exhibited a piece of 2 to 3 
inch lead pipe in which the metal had been entirely 'trans- 
formed into galena, the crystalisation being visible through 
the whole of the specimen. 
The shape of the lead pipe was unaltered, showing that 
the lead had not been exposed to a melting heat, no increase 
of bulk was visible, but the pipe was so brittle as to shiver 
with a blow. The circumstances in which this change was 
effected, as nearly as can be made out, were as follows. 
The pipe had been used for the conveyance of gas ammo- 
niacal water and was sunk under ground. It was in the 
vicinity of a furnace which heated the ground where it 
lay. It had been disused for some years but never 
taken up. When the ground where it lay had to be ex- 
cavated for a new erection, it was found that there had 
been a considerable leak of gas water, as the ground for 
some space was impregnated with ammoniacal salts. About 
25 per cent of the ammonia in gas water being sulphide, 
and the ground being warm, a constant atmosphere of 
sulphide of ammonium would surround the pipe, and this 
seems to have been the cause of the conversion of the lead 
into sulphide, as only that part of the pipe which was in 
the vicinity of the leak was found to be transformed. 
On the Principle of the Electro-Magnet constructed by 
Mr. John Faulkner,” by Professor Osborne Reynolds, M A. 
PROcEEDiNas — L it, & Phil. Soc.—Vol. XV.— No. 2.—- Session 1875-6^ 
