ON MARINE BOILERS. 5 



zinc, &c. to copper sheathing, favoured marine vegetation, and the adhesion of shell-fish, 

 lime, &c. to the ship's bottom ; a disadvantage greater than the evil it was intended to obviate. 

 Iron placed in a copper boiler, for the object alluded to, was speedily decayed, without appa- 

 rent effect : in fact, it was treating the boilers for a distemper which existed only in imagi- 

 nation. Hence no calculable diminution of weight is sustained in copper boilers, from the 

 action of salts, Sec. when held in solution, at sea : but when the interior becomes incrusted 

 with laminae of insoluble calcareous matter, which firmly adheres to the surfaces of 

 the flues, and fire places, and thus certainly protects them from chemical action, and 

 frequently fills the interstices or water-ways of the boilers, it requires violent mechanical 

 means to extract it. In removing these masses, the boilers are much injured ; quantities of 

 rivet heads imbedded in the deposit, and portions of the metal, being alike separated by the 

 instruments used for the purpose. These facts obtain alike in iron and copper boilers. 



10. An evil, however, most sedulously to be avoided, is the accumulation of soot, 

 salt, &c. in the flues ; the chemical action of which is very destructive to boilers. Water, 

 whether cold or boiling, filters through numerous apertures insignificant in dimensions, and 

 almost inseparable from the intricacy of the construction, and mixes with the soot, forming 

 a combination which corrodes the material very rapidly. The heat of the boilers, when 

 employed, evaporates the water, and leaves the salt, 8tc. in a concrete state ; which, when 

 cold, is again dissolved, and recommences its action more formidably. 



On a voyage to the Mediterranean in the months of September and October, 1835, the 

 stay at Malta, on the passage to Corfu, being too short to clean out the flues or to inspect 

 the interior of the boilers, these duties were necessarily delayed till the arrival t Corfu 

 out, and thence to Gibraltar home ; and in both instances there appeared an unusual quantity 

 of soot, &c. in the flues. The congeries of salt, soot, and water was thrown out upon the 

 iron plates of the engine room flooring, where in both instances it remained for nearly two 

 days (the time occupied in properly sweeping) ; when removed and the plates well washed, 

 a pretty and novel phenomenon was exhibited. The iron plates had precipitated the copper 

 from the solution which covered them, exhibiting a permanent metallic surface of copper. 

 This is a valuable practical corroborative of the observation just made concerning the great 

 transmission of the metal, when such solvents are not removed at frequent intervals. I was 

 first attracted to the fact at the above period, have had many opportunities of seeino- it 

 repeated since, and have collected the water, to amuse others by the experiment of the 

 precipitation of copper by iron, from an acid having a greater affinity for the latter. 



The leaks whence the salt resulted, on careful examination, were found so unimportant, 

 that the usual measures to stanch them could not be attempted without the risk of increas- 

 ing the evil ; particularly as this voyage immediately succeeded a general caulking of 

 the flues in parts requiring it, when numbers of screwed rivets were substituted for de- 

 fective ones. 



11. Now, as the defects exist exclusively in the angle pieces and rivets of the bottom 

 of the flues, the top and sides being invariably tight, I have applied a fillet of Parker's or 

 Roman cement in these cases, so as to completely inclose the angle pieces, with their defects, 

 and have thus succeeded in checking the destructive effects of these otherwise trivial, but 

 numerous and incorrigible channels. I have recommended its adoption in other steam vessels, 



