TRANSACTIONS OF THE SECTIONS. 53 
stopcock a certain quantity of the concentrated water of the boiler by the pressure of 
steam, after the admission above of an equivalent quantity of sea-water of ordinary 
density, appears to be, from the reports made, the most easy in practice, the least un- 
successful, and the most to be relied on. But, as in the instance given of the North 
American steamer, it can be viewed only as a palliative. 
Considering the composition of the incrusting matter, and the properties of its 
principal ingredient, the sulphate of lime, a compound soluble in water and in sea- 
water, and deposited only when the water containing it is concentrated to a certain 
degree, there appears to be no difficulty theoretically in naming a preventive. The 
certain preventive would be the substitution of distilled or rain-water in the boiler 
for sea-water; of this we have proof in the efticacy of Hall’s condenser, which returns 
the water used as steam, condensed, after having been so used: but, unfortunately 
for its practical success, the apparatus is described as being too complicated and ex- 
pensive for common adoption. Further proof is afforded in the fact that the boilers of 
steamers navigating lakes and rivers, in the waters of which there is little or no sul- 
phate of lime, month after month in continued use, remain free from incrustation. 
This I am assured is the case with the steamers that have been plying several sum- , 
mers successively on the lake of Windermere. And, it may be inferred, that in sea- 
going steamers, in which sea-water is used in the boiler, or indeed any water containing 
sulphate of lime, the prevention of deposition may be effected with no less certainty 
by keeping the water at that degree of dilution at which the sulphate of lime is not 
separated from the water in which it was dissolved. From the few trials I have made, I 
may remark, that sulphate of lime appears to be hardly less soluble, if at all less, in 
water saturated with common salt than in perfectly fresh water. This seems to bea 
fortunate circumstance in relation to the inquiry as to the means of prevention, and. 
likely to simplify the problem. 
If these principles be sound, their application under different circumstances, with 
knowledge and judgement on the part of the directing engineer, will probably not be 
difficult. His great object will be, in sea-going steamers, to economize the escape of 
water in the form of steam, and thereby also economize heat and fuel; also, when 
fresh water is available, to use it as much as possible; and further, to avoid using 
sea-water as much as possible near coasts and in parts of seas where sulphate of lime 
is most abundant. 
From the incrustation on the boilers of sea-going steamers, the attention can 
hardly fail to be directed to that which often forms, to their no small detriment, in 
the boilers of locomotive railway engines, and of engines employed in mines, and in 
the multifarious works to which steam-power is now applied. 
These incrustations will of necessity be very variable, both in quantity and quality, 
according to the kind of ingredients held in solution in the water used for generating 
the steam. Hitherto I have examined two specimens only of incrustations from the 
boilers of locomotive engines, and a single one only from the boiler of a steam-engine 
employed in a mine—a mine in the west of Cornwall. The latter was fibrous, about 
half an inch thick, and consisted chiefly of sulphate of lime with a little silica and per- 
oxide of iron, and a trace of fluorine. The former were from one-tenth of an inch in 
thickness to an inch. They were laminated, of a gray colour, and had much the ap- 
pearance of volcanic tufa; they consisted principally of carbonate and sulphate of 
lime with a little magnesia, protoxide of iron, silica, and carbonaceous matter; the two 
last, the silica and carbonaceous matter, probably chiefly derived from the smoke of 
the engine and the dust in the air. From the engineer's report, it would appear that 
the thinnest, the incrustation of about one-tenth of an inch, had formed in about a 
week, during which time the locomotive had run about 436 miles, and consumed 
about 10,900 gallons of water. 
On a peculiar Form produced in a Diamond when under the Influence of 
the Voltaic Are. By J. P. Gassiot, F.RS. 
M. Jacquelin was the first to show that when the diamond is submitted to the high 
temperature and influence of the voltaic arc, it quickly becomes converted into a 
_ black carbonaceous matter, having all the appearance of coke. The diamond, when 
in a native state, is an insulator or non-conductor of electricity, but when thus changed 
into coke it becomes an excellent conductor. 
