1815.] into a Substance resembling Plmnbago. 6^ 



bulky sulistance, whicli, when dried and projected on red-liot nitre, 

 burnt rather more vividly than the original substance, but still 

 afforded much oxide of iron. 



It was clear, therefore, that a large share of the metallic part of 

 the pipe had been removed ; and that what remained was composed 

 of iron, plumbago, and other impurities usually present in cast- 

 iron. With the view of ascertaining the cause of the change, I 

 next examined the water from the bed of quicksand, a bottle of 

 which had been sent along with the fragment of pipe. 



The water had a brackish taste, and was of the specific gravity 

 1008. It gave no traces of iron, either with triple prussiate of 

 potash, or succinate of ammonia. I collected the gas from a wine 

 pint of it; but it was lost by accident before being examined. By 

 the usual methods of analysis, a wine pint gavt? 6"4 grains of dry 

 salt, composed of 



Muriate of soda 32 



i magnesia H> 



lime 10 



Sulphate of lime 4. 



Carbonate of lime 2 



6*4 



It is most probably to the agency of the muriates of lirne and 

 magnesia, that v/e a're to ascribe the removal of the metallic part 

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

 salts in discharging writing ink from the lal)els of bottles, to which 

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

 several attempts to restore the legibility of some of the M.S.S. of 

 a most accomplished scholar (the late Mr. Tweddell ot 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 

 Experiments 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, lie observes, explains what happens to 

 cast-iron pipes in pits, the water of which is im[)regnated with 

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

 called, rotten, and may l)e cut with a knife. 



In Cornwall, 1 am iiif(.rmed, cast-iron pipes are disused in many 

 of the mines; but this is owing to the iircsencc tf sulpluitc of 

 copper in the water, the corroding effects of which render it neces- 

 sary to substitute pipes of brass or copper. 



• Abiidjjedand uictlioJi/cJ, vol. iii. [lait iii. s<-ct. 9. 

 £ 2 



