98 
The great diminution of strength at the melting point of 
zinc is remarkable. 
I take the liberty of communicating these results to you> 
as unfortunately I shall be away at the next Meeting, and 
thus shall not have an opportunity of seeing you.” 
Mr. Brockbank remarked that these experiments did not 
affect the conclusions stated in his paper, read at the last 
meeting. He believed that the strength of Iron under 
torsion was most affected by the heat developed by the 
twisting, and that the cooling mixture employed by Mr 
J ohnson would have the effect of making the wire stand a 
greater number of twists by counteracting the excessive 
heat produced by the torsion. 
Mr. Brockbank, F.G.S., exhibited a drawing of the 
machine used by him in his experiments on the strength of 
Cast Iron at different temperatures. 
“Experiments on the Oxidation of Iron,” by Professor 
F. Crace Calvert, Ph.D., F.R.S., &c. 
Some two years since, Sir Charles Fox inquired of me if 
I could give him the exact composition of iron rust, viz., the 
oxidation found on the surface of metallic iron, I replied 
that it was admitted by all chemists, to be the hydrate of 
the sesquioxide of iron, containing a trace of ammonia; to 
this, he answered, that he had read several books on the 
subject, in which the statements referring to it differed, and 
from recent observations he had made, he doubted the cor- 
rectness of the acknowledged composition of iron rust. He 
further stated that if he took a bar of rusted wrought iron, 
and put it in violent vibrations, by applying at one end the 
fall of a hammer, scales would be separated which did not 
appear to him to be the substance I had described. 
This conversation induced me to commence a series of 
experiments which I shall now detail. I first carefully ana- 
lysed some specimens of iron rust, which were procured, as 
far as possible, from any source of contamination. Thus 
