302 EIGHTH REPORT 1838. 



fectually preserved the iron it was in contact with. It is still 

 more remarkable, however, how great the discrepancy in consti- 

 tution of the two specimens of Liverpool brass is, the latter 

 containing an enormous proportion of lead. 



121. It is not difficult to imagine that the mistake of Mr. 

 Hartley has arisen from neglect in observing that which Pro- 

 fessor E. Davy has first pointed out, namely, that iron, or other 

 metals, in its relation to water are preserved from corrosion by 

 covering surfaces, although the water insinuates itself between. 

 Nor does it appear difficult to account for this result. It would 

 appear to be a case of slow or retarded chemical action by the 

 opposition of capillary forces of the same class as slow action, 

 through Becquerel's clay plugs or diaphragms, in which, when 

 once the first portion of air, combined with the fluid between 

 the surfaces in contact, is decomposed and taken up, the chemi- 

 cal affinity of the iron, or similar metals, for it, is counteracted 

 by the capillarity of the flat tube formed by the opposed sur- 

 faces which it is unable to overcome, so as to draw in fresh air 

 to the fluid within, already exhausted of it, 



122. Indeed, if Mr. Hartley be reported rightly, he is stated 

 to have mentioned that '^soil," mud I suppose, lay on the sluices 

 said to have been preserved, and which had to be removed prior 

 to their examination ; if so, there is little wonder they should 

 7iot have sustained corrosion. — Liverpool Journal. 



123. Another, and an extremely probable reason for the mis- 

 take, may have been the supposed preservative surfaces being 

 often smeared with oil or grease, which, for a considerable time, 

 resists the action of sea or fresh water, and protects the metal 

 on which it lies. Indeed, if we could get an air and water-tight 

 covering which would remain so, no further protect(n' for im- 

 mersed or moistened metals need be sought for. 



124. Accordingly, Mr. Arthur Aikin suggested the applica- 

 tion of melted caoutchouc, with or without admixture of oil of 

 turpentine, as a varnish to preserve iron and steel, &c., from 

 corrosion, so far back as 1821. — Gill's Tech. Rep. vol. i. p. 55. 

 And Dumas has proposed the employment of caoutchouc in so- 

 lution as a varnish to the shot and shells in the French arsenals 

 {Comptes Rendus, 1836. p. 373) ; but Payen states that this had 

 been tried by the nmnicipality of Grenoble in the year 1834, and 

 found useless after a short period. 



125. During the experiments already detailed it seemed just 

 possible that Mr. Hartley's might be yet a concealed case of 

 Professor Schoenbein's anomaly of passive iron, or of Dr. An- 

 drew's inactive bismuth, and the writer was just about com- 

 mencing some experiments with a view of elucidating this, when 



