which forms in the Boilers of Steam- Engines. 251 



corresponding to the margin of the vessel, — a deposition such as that 

 produced by silicated fluoric acid gas under the same circumstances. 

 Thus it was not dissipated by heat nor dissolved by water, and yet 

 admitted of removal by abrasion, either entirely or in great part ; — 

 the former in the instance of the platina foil, the latter in that of 

 the glass. Besides the ingredients above mentioned, I may add that, 

 in many instances, oxide of iron, the black magnetic oxide, was found 

 to form a part of this incrusting deposit, collected in one or more thin 

 layers ; and further, that in some, especially of steamers navigating the 

 narrower and least clear part of the British Channel, the depositions 

 presented a brownish discoloration produced by the admixture of a 

 small quantity of muddy sediment. Incrustation so discoloured, I 

 may remark, are reported to be most difficult to detach. 



I have said that the incrustations, with few exceptions, were similar 

 in their structure, and that that was crystalline; — it was not unlike the 

 fibrous variety of gypsum of the mineralogists. — The specimens re- 

 ceived, as might have been expected, varied very much in thickness, 

 viz., from oneline and less to half an inch. I have endeavoured, by a set 

 of queries which I had distributed, to obtain information respecting the 

 exact time in which the incrustations were formed, and under what cir- 

 cumstances; but with partial success only, owing, it may be inferred, 

 to a want of exact observation. In one instance, that of the North 

 American mail-ship Europa, which arrived at Liverpool on the 15th 

 of November, at 4 p.m., having left Boston on the 7th of the same 

 month at 9 a.m., an incrustation was found in her boiler of about 

 one-fiftieth of an inch in thickness ; and it is stated that an incrus- 

 tation of about the same thickness was found on her outward voyage. 

 This example may aid in giving some idea of the degree of rapidity 

 with which the incrustation is produced, at least in the Atlantic, 

 with the precaution of " blowing off" every three hours, and with the 

 " brine pumps" kept in constant work. In other seas, especially 

 contiguous to shores, and more especially of shores formed by volcanic 

 eruptions, it is probable, cceteris paribus, the rate of the deposition 

 of the incrusting sulphate of lime will be more rapid. The results 

 of the trials of several portions of sea-water taken up on the voyage 

 from the West Indies to England, noticed in the paper of mine already 

 referred to, are in favour of this conclusion. 



To endeavour to prevent the deposition of the incrusting matter or 

 to mitigate the evil, various methods, it would appear, have been had 

 recourse to, — some of a chemical kind, as the addition of muriate of 

 ammonia and sulphate of ammonia to the water in the boiler, — without 

 success, as might be expected; — others, of a mechanical kind, with par- 

 tial success, — as the introduction of a certain quantity of saw-dust into 

 the boiler, or the application of tallow, or of a mixture of tallow and 

 plumbago to its inside, to prevent close adhesion, and the more easy 

 separation of the incrusting matter either by percussion, using a 

 chisel-like hammer, — or by contraction and unequal expansion, by 



