306 EIGHTH REPORT — 1838. 



or alkaline earth would be admissible and valuable if found 

 effective preservers of iron; for instance, lime-water might 

 readily replace the bilge-water in steamers, whose action is at 

 present so destructive to the holding-down bolts, blow-off pipes 

 and cocks, boiler bottoms, coal bunkers, &c., and to the de- 

 composition of which in a great degree the peculiarly offensive 

 smell of the bilge- water of steamers is owing. There is no rea- " 

 son to assume that dilute lime-water would have any injurious 

 action on the timbers of the ship. 



136. Dr. Andrews' and Schoenbein's experiments, however, 

 in which a metal becomes capable of rendering passive or of 

 protecting in certain cases another, alt/tough itself not acted 

 on, give hope that protectors of this kind may yet be found and 

 practically applied to iron ; and hence it is in this direction that 

 our efforts should be bent with most energy in seeking to pre- 

 serve metals from oxidation, namely, to obtain a mode of elec- 

 tro-chemical protection, such that, ichile the metal shall be 

 preserved, the protector shall not be chemically acted on, and 

 whose protection shall be invariable. 



137, In illustration of this I may adduce a very interesting 

 experiment of Becquerel and 'Dunms {Comptes Rendus, 6th Feb. 

 1837) : " Having taken a flask half filled with distilled water, in 

 which was dissolved -j-Ao ^f potass, they plunged into it a slip 

 of perfectly polished iron, and another of gold ; to each was fixed 

 a wire of the same metal passing through the cork. The flask 

 was sealed with all possible care to prevent the access of air. 

 Seventeen months afterwards the iron preserved all its bril- 

 liancy, no tubercles had formed on it, and every thing indicated 

 that it had undergone no appreciable alteration." 



When the gold and iron wires were placed in communication 

 with a multiplier with a short coil, an immediate deviation of 

 35° was produced, and the magnetic needle having oscillated 

 awhile, came to rest again at zero. On interrupting and again 

 re-establishing the communications it remained motionless, but 

 on leaving the circuit open for a quarter of an hour, and again 

 closing it, the needle deviated 25°, and after remaining inter- 

 rupted for half an hour, the deviation amounted to 35° again. 



The experiment was repeated, and always with accordant re- 

 sults. The current produced is then the result of a discharge 

 like that of a Leyden phial. 



Thus, when the iron is in contact with the alkaline water, the 

 metal takes by degrees a charge of negative electricity, and the 

 water a charge of positive electricity, as if there had been a 

 chemical reaction between them. (De la Rive in fact considers 

 that it is due to a chemical action, though excessively slow.) 



