197 
but regularly purchased by him in the market for his oum 
use as an iron founder, and the importance of this was to be 
found in the fact that several results were entirely at vari- 
ance with Mr. Fairbairn's experiments on iron from the same 
works. It did not prove that Mr. Fairbairn was incompetent 
to conduct such an experiment, but really and truly that he 
had not the means of doing so in such a satisfactory manner 
as Mr. Todd had done. The experiments were highly im- 
portant to the iron founder, because, although the practice 
and effect of the mixino^ of irons made with different mate- 
rials had been long known, it was not so with respect to the 
running it into moulds at particular temperatures. He was not 
aware whether any experiments had yet been made on this 
point, but the strength of castings, when the iron was run 
into them at a cool temperature, it seemed was much dete- 
riorated. He could dwell longer upon the subject, from the 
interest which it possessed, but he hoped to hear some ob- 
servations from gentlemen resident in Leeds, to whom the 
subject was quite of as much importance as to himself. 
The Chairman inquired whether any philosophical re- 
port had been written upon the subject ? 
Mr. Hartop believed not. The mixing of two irons had 
a very considerable effect on the crystalization while cooling, 
by which it was, he thought, that the strength of the iron 
was very considerably influenced. Where a fracture took 
place in a casting on a large scale, there was invariably a 
flaw or defect in it, and it was astonishing what a material 
effect upon the strength of it a very small air bubble would 
produce. A bar of iron a ton weight had been known to 
break where an air bubble had existed to not a greater extent 
than a small pea. The Yorkshire iron had besides another 
advantage, — that the castings were more permanent in quality, 
as compared with most other irons, whether made by hot or 
cold blast. As an iron master, his experience had led him 
