OLD COAL-PIT WATER UPON IRON, 



31 



" It is most probably to the agency of the muriates of lime and 

 magnesia, that we are to ascribe the removal of the metallic part of 

 the pipe. 1 have often remarked the effect of solutions of these 

 salts in discharging writing ink from the labels of bottles to which 

 they have been accidentally applied : and I was lately baffled in 

 several attempts to restore the legibility of some of the MSS. of a 

 most accomplished scholar (the late Mr. Tweddell, of Trin. Coll., 

 Cambridge) which had lain some time under sea water, abounding, 

 as is well known, in muriate of magnesia. The texture of the paper 

 was entire, but the iron basis of the ink, as well as the gallic acid, 

 was entirely removed. 



" In that copious repository of valuable knowledge, Dr. Priestley's 

 Eocperiments and Observations on Air, some facts are stated that bear 

 an analogy to the one which I have described. Cast iron nails, he 

 found, dissolved very slowly in diluted sulphuric acid ; and left a 

 large proportion of black matter which had the original form of the 

 nails. This experiment, he observes, explains what happens to cast 

 iron pipes in pits, the water of which is impregnated with vitriolic 

 acid ; for, in time, they become quite soft, or, as it is called, rotten, 

 and may be cut with a knife. 



" In Cornwall, I am informed, cast iron pipes are disused in many 

 of the mines ; but this is owing to the presence of sulphate of copper 

 in the water, the corroding effects of which render it necessary to 

 substitute pipes of brass or copper. 



"The following fact, which was lately observed at the printing 

 works of a friend of mine, belongs to a different class of phenomena, 

 and is, perhaps, to be accounted for by galvanic agency. In order 

 to confine the heat in some cast iron steam pipes, they were placed 

 in a trough or gutter made of bricks, into which powdered charcoal 

 was tightly rammed. At a place contiguous to a joint, formed by 

 bolting two flanches together, a leak had happened, and when the 

 iron pipe was taken ap, it was found, in the neighbourhood of the 

 leaky part, to be perfectly soft and rotten. I was not able to obtain 

 an opportunity of examining the nature of the change by an experi- 

 ment on the altered iron." 



The facts which will be brought before you in this com- 

 munication occurred in the deep pits of the Pendleton 



