ON COPPER BOILERS. 11 



to the substitution of screwed rivets, which at the best are a poor substitute for a rivet of the 

 original kind. 



I have found, that when sufficiently acted on chemically, the above observations equally 

 apply to the joints of the plates with the "angle irons," the apertures formed between them 

 being sometimes entirely in the plate, which is thus decayed so as to receive copper pins of 

 considerable size. This is the worst state of the evil ; for the water by its pressure, in addition 

 to that of the steam, acts mechanically as well as chemically in forcing its passage, which, 

 if not timely stopped, will certainly eat transversely through the plate. It is also worthy of 

 note, that the flues are found perfectly tight over-head and along the sides ; the lower parts 

 and the " angle iron " of the bottoms only, and that in spots difficult of construction, yielding 

 to the action. 



After a lapse of six years of active employment, 1 can safely pronounce the parts above the 

 bottom of the flues and fire-places, exposed to the constant action of the fire and water, to 

 retain nearly their original thickness ; I say nearly, because the deficit cannot be actually 

 observed or estimated unless by weight. From the line, however, which the usual length of 

 voyage permitted the salt to accumulate downwards to the bottom of the flues, that is, to the 

 extent of thickness of salt deposited, corrosion has evidently taken place, so much as to 

 threaten the security of parts originally well manufactured, even in the face of caulking, &c. 

 This evil necessarily continued in action for some months in the Mediterranean, when 

 employed between Malta, Egypt, and Syria, on an average of twenty to twenty-four days per 

 month at sea, in the total absence of Roman cement ; which, when procured, again kept the 

 flues tight and dry. The advantages of the cement, here exhibited, suggest its use not only 

 when a boiler is defective, but when perfectly new. 



I should propose, that when tried and found perfect, the flues should be well cleaned, and 

 a flooring of cement applied by proper persons, so as to include the "angle irons;" tiles 

 should then be imbedded nicely, forming a perfect surface from the chimney to the furnace, 

 or, which was the method I adopted, a fillet should be applied all round the "angle irons," 

 with a flooring beneath the funnel. Thus the water from the chimney, impregnated with the 

 matters of the soot, would be entirely prevented, in the beginning, from acting on the bottoms 

 of the tubes ; and any spot beneath, being disposed to " weep," would be prevented till it had 

 been permanently filled with sulphate of lime or other matter, which, on the contrary, would 

 be forced onwards into the bottoms of the flues if water could freely pass. It would have 

 another advantage, it would afford facility in sweeping the flues, and would occupy the 

 intricate parts, from which the soot is never thoroughly cleaned. No very material loss of 

 heat would be sustained by this application, the fires not being calculated to reverberate 

 downwards to a great extent: on the contrary, I have often sent wood into the flues, which 

 has been withdrawn, merely charred; a proof that the bottoms of the flues, those leading 

 directly from the furnaces excepted, contribute little to steam generation, even before any 

 deposition of soot has taken place. 



I think it probable, that "weeps " in the tops and sides of the flues, before alluded to, are 

 first checked by the intensity of the fire acting on the water as it oozes, when the lime subsides 

 and hardens to cement ; for there is no reason why " weeps " should not have existed in 

 equal abundance in these places, as well as in the bottoms ; but it is certain that none have 

 been exhibited. 



