52 REPORT—1850. 
and the West Indies. Iam promised specimens from the Red Sea and the Indian 
Ocean, but these I have not yet received. 
The character and composition of the incrustation, whether formed from deposition, 
from water of narrow seas, or of the ocean, I have found very similar, with few ex- 
ceptions crystalline in structure, and, without any exception, composed chiefly of 
sulphate of lime, so much so, indeed, that unless chemically viewed, the other ingre- 
dients may be held to be of little moment, and rarely amounting to five per cent. of 
the whole. 
From two specimens of incrustation from the boilers of steamers crossing the At- 
lantic, one of which you sent me, in which you had detected a notable portion of 
fluorine, judging from its etching effect on glass, I also procured it; it was in com- 
bination with silica; and I procured it also so combined from two obtained from 
steamers navigating our own seas, one between Dundee and London, the other be- 
tween Whitehaven and Liverpool. Of this I had proof by covering with a portion of 
glass or platina-foil a leaden vessel charged with about 200 grs. of the incrustation 
mixed with sulphuric acid, and by keeping the glass cool by evaporation of water from 
its surface, and by supplying moisture for the condensation of the silicated gas by a 
wet band round the mouth of the vessel. After about twenty-four hours under this 
process, a slight but distinct deposition was found to have taken place, 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 dis- 
solved 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 the incrusting deposit, 
collected in one or more thin layers; aad further, that in some, especially of steamers 
navigating the narrower and least clear part of the British Channel, the deposition 
presented a brownish discoloration, produced by the admixture of a small quantity of 
muddy sediment: incrustations 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 struc- 
ture, and that that was crystalline; it was not unlike the fibrous variety of gypsum 
of the mineralogists. ‘The specimens received, as might be expected, varied very 
much in thickness, viz. from one line 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 circumstances, 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 steam-ship “ Europa,” which arrived at 
Liverpool on the 15th of November, at 4r.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 incrustation of about the same thick- 
ness was formed 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 eruption, it is probable that, ceteris 
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 re- 
ferred 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 
partial success,—as the introduction of a certain quantity of sawdust into the boiler, or 
the application of tallow, or of a mixture of tallow and plumbago to its inside, to pre- 
vent 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 
means of flame kindled with oakum after emptying the boiler and drying it, Ofall the 
methods hitherto used, that of “ blowing off,” that is, the discharging by an inferior 
