152 THE ACTION OF SEA-WATER UPON CAST-IRON. 
heated and smoked in the course of a minute. In another case 
when a considerable quantity of it had been heaped together it 
undred specimens of cast and wrought iron and steel, as well as 
to test the advantages of various protective paints and varnishes 5 
they also contain the results of experiments made to ascertain the 
protection afforded by zinc, &c., to iron structures in contact with 
water. 
Mallet states that Priestley was one of the first of those a 
observed this conversion of cast-iron into a plumbago-like ee 
mixed oxide of iron and carbonaceous matter, and peat 
residues frequently but not invariably became hot or spontan y 
inflammable on exposure to the air. Mallet states that de 
tain circumstances even the purest malleable iron is conver Te 
Ae ete, 1 RRS OE eS Bind i tos instances. The bt 
d in the a7") 
mentions that some cannon-balls which were foun ee 
the site of the battle of La Hogue had, after an im ia 
years, been converted into plumbago to the depth of an their 
some cases and right through in others ; assum? 3a.lb 
diameter to have been about 6} inches, the usual size depth of 
shot, he points out that the iron had been destroy: pee rapid 
3} inches during the above number of years,—® much mor? isle 
rate of action than he obtained from his special expe? ae 
The foregoing will probably suffice as instances mie Mallet’s 
i 
sea-water, brought about more or less by reage! Mr ‘merely 
