52 Mr. Noad ofi the Hydrates of Barytes and Strontia, 



quite agree with Dr. Schoenbein that it seems to belong to a 

 distinct class of phaenomena. It differs from iron in these 

 particulars: 1st, Platina wire will immediately stop its effer- 

 vescing action in nitric acid sp. gr. 1*2, though it will not pre- 

 vent its slow oxidation, as is proved by its turning black, and 

 also by appeal to the galvanometer : the same metal will not, 

 under similar circumstances, protect iron, as has sufficiently 

 been shown. 2ndly, I have observed, that when bismuth has 

 once had its action with the acid lessened, it does not regain 

 it for a long time, even after the surface has bee?i removed 

 by fling ; but by degrees its original character is restored : 

 and, lastly, when substituted for the bent iron wires, as in the 

 experiments above described, it allows the electrical current 

 to pass quite as freely as active iron wire. 



These are the principal facts I have thought worth com- 

 municating. I have made many other experiments with vol- 

 taic piles of various sizes, but the results at which I have arrived 

 have in general coincided so closely with those described by 

 Dr. Schoenbein, that I shall not trouble you with a relation 

 of them. In conclusion, however, I would strongly recom- 

 mend those who may have an opportunity of procuring cobalt 

 and nickel in a state of purity, and in sufficient abundance, to 

 repeat these experiments, substituting those metals for the 

 iron ; and I cannot help thinking, from the general chemical 

 analogy between these three metals, that something interesting 

 may thereby be elicited *. I am, yours, &c. 



Shawford. Dec. 11, 1837. * Henry M. NoAD. 



P. S. — I take the opportunity which this letter affords me 

 to state, that through the kindness of Mr. J. Denhara Smith 

 I have been furnished with some crystals of the hydrates of 

 barytes and strontia from the specimens on which his experi- 

 ments were made; and it is due to him and to the public to 

 state, that the results of my analysis have agreed so closely 

 with his, that there can be no doubt that the constitution 

 assigned by him to these hydrated metallic oxides is perfectly 

 correct. I have, nevertheless, repeated also the analysis of 

 the crystals I obtained, with the same results as stated in my 

 letter on that subject; and I can therefore only attribute the 

 difference to the extreme difficulty of depriving these hydrates 

 thoroughly of uncombined water. [See Lond. & Edinb. Phil. 

 Mag. vol.ix. p. 87; vol.xi. p. 301.] 



• It must be recollected, however, that Professors Schoenbein and Degen 

 were convinced, by their experiments, that the peculiar condition cannot 

 be excited either in cobalt or in nickel. See our last Number, p. 547.— 

 Edit. 



