4 APPENDIX. 



this was justified on each arrival ; hence no time was thus wastefully consumed. The order 

 for laying-to every three or four days, to blow the boilers entirely out, at sea, is still in force 

 in the navy, and forms part of the instructions to officers commanding her Majesty's steam 

 vessels ; but how far this is necessary, the fact of having never blown off entirely at sea will 

 explain : I believe the practice is now rarely resorted to, although some are still inclined 

 to think it necessary. 



7. I am also decidedly of opinion, that it is unnecessary to prescribe any specifics for the 

 prevention of deposit or chemical action in copper boilers affixed to marine engines, such as 

 the introduction of large masses of iron, &c. ; the same effects exhibiting themselves in iron 

 as well as copper boilers, when submitted to the influence of a highly concentrated solution 

 of saline matter, 8cc. in a constantly boiling state, viz. deposition of the salts, 8cc. and 

 ultimate destruction of the boilers. As a proof of the fallacy of such applications, the incision 

 I made in a copper boiler with a chisel was not obliterated or sensibly diminished by the 

 action of the water alone, at the end of three years ; the boilers, during the time, being 

 employed in the North Sea and Channel, and free from incrustation, except a film with which 

 the tubes were whitened. After the experiments before alluded to, the boilers were con- 

 stantly employed in the Mediterranean, and on the Lisbon service ; and were not in any way 

 submitted to the form of cleaning out, till the expiration of the third year : a very slight 

 scale was then removed, leaving the surfaces scaled, precisely as when rolled. 



8. The remarkable preserving influence these calcareous matters possess over copper 

 and other metals has recently been exhibited in the bronze guns, raised by the enterprising 

 Mr. Deane from the Royal George at Spithead ; which properties, if generally known, 

 might be available for some useful purpose. I give the notice extracted from the ' Mechanic's 

 Magazine :' " The guns are incrusted with a coat of lime about the twentieth of an inch 

 thick, to which several oysters have attached themselves ; but these, as well as the calcareous 

 coating, separate very easily from the metal, leaving the gun perfectly clean and sharp in 

 its castings." It observes also, "that the rings of wrought iron attached to the breech 

 were totally decayed, the cast iron shots and wads being in a perfect state of preservation." 

 The preservation of the shot is easily accounted for, being pent up by its wad ; but the 

 galvanic agency of the iron, exposed to the water, neutralized its destructive effects on the 

 gun ; and hence the calcareous formation, which, when the existence of the iron should 

 totally cease, would certainly defend the bronze from all attacks of the sea. The adhesion 

 of oysters favours this view of the circumstance. 



Since noting the above in the Mediterranean, I have seen in the arsenal at Woolwich 



O 



several of the guns alluded to, which in every respect confirm what is stated in the 

 extract. The condition of these guns is a fair specimen of the interior of a boiler 

 after a few voyages to sea, except that in the case of the boiler the surfaces are incrusted 

 more uniformly : the coating however in both instances equally protects the surfaces from the 

 destructive attacks of the sea water ; but the causes of deposition are different : in one case 

 it is effected by galvanic influence ; in the other by depriving the water of a component part, 

 by the simple operation of boiling. 



9. The experiments of Davy on copper sheathing induced many to attempt the applica- 

 tion of the principle to other purposes, and marine boilers (copper) proved to be a failure 

 of this description ; for the electric action which was induced by the application of cast iron, 



