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colliery near Newcastle, the water of which was strongly impregnated 
with the muriates of lime, magnesia and soda. The specific gravity of his 
specimen was 2.155, the decomposition had therefore evidently not been so 
complete as in the present instance. It had been known, so long since 
as in the time of Scheele, that though the affinity of iron for muriatic 
acid is less than that of soda, lime, or magnesia; yet when either of 
these substances, in the state of a muriate, is present in great excess, 
it is itself decomposed and a muriate of iron is formed. Hence Dr. 
Henry seems to have attributed the corrosion of the cast iron solely 
to the action of the muriates of lime and magnesia. But it has been 
recently proved by Dr. Marcet that muriate of lime does not exist in sea 
water; and though, by long continued action, the muriate of magnesia 
alone might possibly be adequate to the decomposition, without having 
recourse to galvanic agency; yet, as muriate of soda makes a powerful 
galvanic circuit between dissimilar metals, which undoubtedly existed in 
contact in the present instance, and probably in the case cited by Dr. 
Henry (as the corrosion seems to have taken place at the junction of 
two pipes) there appears to be no necessity for the rather improbable 
supposition that chemical affinity alone had effected so complete a de- 
composition in so short a time. How far the original formation of 
native graphite may be attributed toa similar cause, is so much a- matter 
of hypothesis, that I shall not waste the valuable time of this Society by 
attempting to discuss it. 
