272 REPORT—1840. 
ture here adopted, is more also than a mere set of arbitrary 
visual distinctions, inasmuch as each class I have made holds a 
constant relation between the character of its fracture and its 
chemical constitution. Ihave also given the general working 
character of each such class of cast iron, by which, however, it 
is not to be understood, but that occasionally a mtxed cast tron 
may be found, possessing all these characters in working, and 
yet breaking with a slightly different fracture. The working 
characteristics given are, however, on the whole, correct. 
279. The present communication, I would hope, in some de- 
gree fulfils the desire of the British Association as to a portion 
of this inquiry, and will be found not devoid of use to the prac- — 
tical engineer. I do not purpose to enter at all in the present 
Report upon the chemical consideration of the changes which 
iron occasionally undergoes by the action of various solvents in 
passing into a substance analogous to plumbago, nor of the or- 
ganic and other products which result from such reactions ; 
these I hope to bring forward on a future occasion, along with 
the results of all the other trains of experiment in progress or 
contemplation, and of the second immersion of all the cast and 
wrought irons for a period of two years, which will expire in 
January 1842. The results of their first immersion are now 
given, and with the results of the experiments now in progress, 
on wrought iron and steel, together with a review of the whole 
subject in its purely chemical relations, will, I expect, com- 
plete our researches. 
280. The latter experiments on wrought iron and steel have 
been for some months in operation ; and the tables of data be- 
longing to them, which best indicate their nature and extent, 
have been presented; but it is not necessary to publish them at 
this time, as the only results of this series actually completed as 
yet, are the specific gravities. These are given in Table XVI. 
The maximum specific gravity is that of tilted blister steel, 
made by the Mersey Steel Company, which is = 7°8461. The 
minimum specific gravity is that of cast steel in the ingot, be- 
fore tilting, which is =,7°4413 ; it contains microscopic vesicles. 
The specific gravity of the iron from which both were made, is 
=7'5839. 
From this Table it appears, that both in wrought iron and steel 
the density is increased more by hammering than by rolling, and 
that the densest specimens of both metals break with a fibrous 
or very fine crystalline fracture, while the least dense have a coarse 
crystalline or lamellar fracture. 
281. Experiments already detailed having demonstrated the 
great rapidity with which iron of every sort is corroded while 
