262 EIGHTH REPORT — 1838. 



from Charles Horsfall, Esq. to Dr. Traill, in which bars of cast 

 iron of 3 inches broad by 1 inch thick, which formed protectors 

 to the copper of a vessel, to the amount of abo'ut ^no ^^ its sur- 

 face, were, in a voyage of not quite five months, to Jamaica and 

 back, converted into plumbago to the depth of half an inch ; it 

 heated on being scraped and exposed to the air when the ship 

 first went into dock. Mr. Brande, in the Quarterly Journal, 

 vol. xii., describes an iron gun which had long lain in water as 

 converted into plumbago to the depth of an inch. I have also 

 been favoured by my friend, Mr. Firmston of Glasgow, with a 

 piece of similarly changed cast iron from the false keel of the 

 John Bull, East Indiaman. In four years this piece of 1| inch 

 by 4 inches was completely altered through. Its specific gra- 

 vity is 1*259. I have not yet been enabled to determine the 

 composition of this specimen, or that from the wrought iron 

 before alluded to. 



25. Mr. Pepys found cast iron similarly changed by the ac- 

 tion of pyroligneous acid (Gill's Tech. Rep., vol. iii.) ; and I 

 have myself obtained specimens so produced by this acid in a 

 state of vapour. The same change is produced by the vapour 

 disengaged in the roasting of coffee ; and a curious case of simi- 

 lar action of sherry wine on wrought iron and steel is to be 

 found in Thomson's Annals. It is also well known that the 

 cast-iron plates at first used in the interior of Coffey's Patent 

 Still, were I'apidly converted into plumbago by the action of 

 the low wines and proof spirits. Much more lately cannon 

 shot have been found immersed in the sea, near the site of the 

 battle of La Hogue, converted to the depth of an inch into plum- 

 bago, or, according to another statement, all through. The 

 battle of La Hogue took place in May 1 692 ; hence these shots 

 have lain in the sea for a period of about 145 years; it is pro- 

 bable they were thirty- two pound shot, and, if converted into 

 plumbago all through, this fact shows that some cast irons may 

 be wholly destroyed in the above period by sea water, to the 

 depth of 3^ inches, — a 32 lb. shot being about 6j in. in diameter. 



26. I have thus collected and given at a tedious length nearly 

 all the cases of this singular change published ; they serve as an 

 index for future experiments, and they show how very little we 

 know of the real nature of the phenomena. It is equally ob- 

 vious that, from the want of precision and of data as to time 

 and surface, &c. in most of the statements, no information is 

 afforded of any use to the engineer. 



It strikes one at once, that every author hitherto who has 

 studied this subject has wholly omitted any consideration of a 



