OLD COAL-PJT WATfiB UPON IRON. 



2d 



exposure. Its specific gravity is l'77S. This fact militates 

 against an observation made by Mr. Hatchett, and repeated 

 by M. Becquerel, that anchors and other objects of forged 

 iron sustain no alteration in sea water but oxidation ; from 

 which we must suppose that the contact of iron and plumbago 

 in the cast iron, produces a current which accelerates the 

 action of the latter. 



In Mr. Mallet's report before alluded to, he only mentions 

 one case of the effects produced by waters in mines upon 

 cast iron. This was given by one of the most distinguished 

 members of this Society, the late Dr. William Henry, F.R.S., 

 and is printed in vol. v., p. ^, of the Annals of Philosophy. 

 It is entitled — " On the conversion of cast iron pipes into a 

 substance bearing some resemblance to plumbago." As this 

 communication bears so much on the subject of this paper, 

 and appears to be but little known, I shall give it entire. 

 He says — 



" I \vas lately requested by a gentleman who resides in the neigh- 

 bourliood of Newcastle-upon-Tyne, to examine the nature of the 

 change eflfected in a cast iron pipe, placed in the shaft of a coal 

 mine near that town. In sinking the shaft it was necessary, as 

 sometimes happens, to put down a curb, or cylinder, of cast iron, in 

 order to support a bed of quicksand: and into a suitable opening 

 in this cylinder, the cast iron pipe, three inches diameter, was 

 bolted by means of a fianche at its extremity. Its use was to 

 allow an exit to the water and gas which issued from the stratum 

 of quicksand, 



" The fragment of the pipe with which I was furnished was of a 

 dark grey colour : its inner surface was smooth and black ; and its 

 outer surface had a thin ochrey incrustation. The usual fracture of 

 cast iron was exchanged for an earthy one, except near the centre of 

 the mass, where somewhat of the usual texture of cast iron was still 

 visible. It was soft enough to be easily scraped with a knife, and 

 was readily broken by a slight blow of a hammer. Some parts of it 

 left a black trace on writing paper, but destitute of the lustre which 

 the traces of plumbago exhibit, 



