ON THE ACTION OF AIR AND WATER UPON IRON. 269 
that the softer cast irons might be alloyed with a minute quan- 
tity of some other metal, which should produce a compound 
still more electro-positive with respect to hard cast iron than 
before. This view is supported by some facts recorded by Ber- 
_ thier, in the Annales des Mines, tom. xi. p. 512, third series. 
_ Soon after Algiers was taken by the French, some ancient shot 
and shells were sent to France to be recast, which had been 
_ discovered in the arsenal. They were found, however, unfit for 
"service; the metal of which they were composed was full of mi- 
_ nute cavities, so brittle as to be easily pulverized, white and 
_lameliar. Analyses of the shot and shells gave the following 
results in 1000 parts: 
Shot. Shells. 
Azsenie)) :5))40) 0. O"27O428s.44.0  O7098 
Carborie ae he) 2% POOL es eksieode vo OLS 
0°280 0°113 
They contained neither sulphur, manganese, calcium, nor sili- 
‘con. Specific gravity of shot = 7°650, of shells = 7°585. 
‘The cast iron alloy of which they were formed was found by 
Berthier to oxidate, when exposed to air and water, with un- 
usual rapidity : he supposes these projectiles to have been cast 
in Spain, of iron made from mispikel or arseniuret of iron. 
_ 271. I now proceed to make some remarks upon the specific 
gravities of cast iron, wrought iron, and steel, which follow in 
the accompanying tabulated results. In Table XI. are col- 
_ lected the specific gravities of all the cast irons of the preceding 
experiments. These specific gravities have been taken with an 
mnusual amount of care, and by a new method, described in 
the former Report*, which possesses some decided advan- 
tages in point of accuracy and convenience. They have all 
een taken on equal-sized cubes of the several cast irons cut 
j the planing-machine from bars of equal size, viz. one inch 
re, and cast in the same way, at the same temperature 
arly, and cooled at the same rates; all of which precautions 
_ are essential to procuring correct results. 
_ 272. Many of my specific gravities do not agree with those 
iven by Dr. Thompson or those of Mr. Fairbairn, contained 
heir respective reportst. This may arise possibly from Dr. 
mpson’s specific gravities having been taken from pieces of 
raw pig-iron, or castings of a different size from those I 
d, or of various dimensions with respect to each other. In 
r. Fairbairn’s case, probably from the circumstance that (as 
Bs S71: T In vol. vi. Report of the British Association. 
