have in the diminishing the making of steam, according to the quantity of fuel consumed?-It would require considerably more fuel to raise the same quantity of steam, but I am not able to give a proportion.

"Do these crusts contribute to hasten the burning of the bottom of the boiler?—Yes; by preventing the transmission of the heat through the bottom of the boiler, the metal itself becomes much hotter than it ought to be, and consequently burns away much sooner than it should do.

"By so much heat not being transmitted through the bottom of the boiler, it follows that the flues must become hotter than they ought to be, and thereby be considerably injured?—Yes."

Mr. Field, in his evidence, at page 155, given at the same time, says, in reply to the following questions:

"Do you find any inconvenience in your engines, by the formation of salt in the boilers after the voyages?—Yes.

"Have you contrived any remedy for that inconvenience? -Nothing, excepting changing the water very frequently, and affording the greatest facility for that purpose to the engine-keeper."

And, again, at page 186:—

"Does not it require a very diligent attention, on the part of the engineer, to keep the engine constantly in good order? -Yes.

"What are the principal injuries that may arise from neglect on their part?-I think the greatest evil to be apprehended is to the boiler; their neglecting to feed it properly with water, and change it frequently.

"What is the consequence of that omission?-Burning the fire-place and destroying the flues.

"And also burning the boilers?—Yes."

Mr. Farraday, in addition to his evidence, from which the extracts have been taken, gave in a paper on a subsequent day to the Committee, containing the result of further and more accurate experiments. The following forms part of this interesting paper:

66

Royal Institution, May 7th, 1822.

"The following remarks are intended to accompany the evidence I have been called upon to give before the Committee, on Holyhead Roads.

“With regard to the composition of sea-water, the following numbers are very nearly correct, and accord with the best analysis. Its specific gravity varies, but may be estimated, as a mean, at 1027, pure water being 1000. When of a specific gravity of 1027.2, being such as I used in my experiments, one cubic foot of it weighs 1026.265 ounces avoirdupois, and contains—

Ounces.

25.762

3.282

2.212

1.013

32.27

"When any of these salts, in their pure and separate state, are dissolved in water, and left in contact with iron, or are boiled with wrought iron in a close vessel, analogous to a steam-engine boiler, corrosion of the iron takes place, and an oxide of that metal is formed. The effect even takes place at common temperatures, and is much increased by the free access of air. In consequence of this power of corrosion, which belongs also to the solutions when mixed, as they are in sea water, all iron boilers, in which sea water is used, will be subjected to a much more destructive process than when fresh water is used in them, notwithstanding any de

gree of care that may be given to them; and if care is not given, then other serious causes of injury arise, which greatly add to the bad effects necessarily attendant on the use of sea

water.

"When a boiler, charged with sea water, is heated, and steam sent off from it, the following effects take place within: the water becomes more and more concentrated, acting at the same time more powerfully on the iron. When the concentration arrives at a certain point, the sulphate of lime begins to deposit, and forms crusts on the bottom and sides of the vessel. Continuing the evaporation, the water becomes so much diminished in quantity as to be unable to hold even the common salt in solution, and it begins to deposit. During the whole of this evaporation the temperature of the fluid has been rising, and it requires more heat to make it boil than it did before. Ultimately, if the operation be continued, the salts become dry in the boiler, the temperature rises, and when it attains from 270° to 300°, the muriate of magnesia is decomposed, its earth or magnesia left free, and its muriatic acid sent off in the state of gas.

*

*

*

*

*

"One bad effect produced by this state of things, is the burning of the bottom of the boiler and flues. The heat, in traversing the bottom of the boiler to reach the water, has also to pass through the crust of deposited matter, and, this being of bad conducting powers, obstructs its passage, and causes its accumulation in the metal itself, which, of course, suffers from combustion more rapidly, in proportion to the temperature: at the same time, the flame and smoke, not being able to give off their heat to the already heated metal, pass on into the flues, at a temperature far above what they ought to do, and burn them.

"Another evil is, that less steam is raised; for the crust,

acting as a barrier between the fire and the water, prevents the latter from receiving that accession of heat which it ought to do; and the quantity of steam produced is proportionably less. Hence there is a waste of fuel in getting steam, or else there is a want of steam; and at the same time there is a burning of the boilers."

CHAPTER VII.

CONCLUDING OBSERVATIONS.-CERTIFICATES

USELESS IF AT VARIANCE WITH PRINCIPLES.-PREJUDICE MUST BE REMOVED BY ANTICIPATING OBJECTIONS.-SUMMARY OF THE ADVANTAGES OFFERED BY THIS PLAN. -IMPORTANCE OF IT FOR STEAMERS DISTANT FROM ENGLAND.-SAVING OF NEARLY ONE-THIRD OF FUEL, EVEN IN RIVER WATER.-CRITERION OF PERFECT INVENTIONS, SIMPLICITY IN THE MEANS, EFFICIENCY IN THE END.-MR. WATT'S SEPARATE CONDENSER ANALOGOUS.-SYMINGTON'S INVENTION DOES FOR STEAM NAVIGATION, WHAT THAT DID FOR THE STEAM ENGINE.

It is very probable the writer may not have succeeded in convincing others, that this invention is of the same importance as he himself attaches to it. He has been, however, far more desirous of demonstrating, in the clearest manner, the simplicity and reasonableness of the invention, by entering upon somewhat too much at length, perhaps its mode of action, than of parading a long list of certificates. These are wholly unnecessary where the principle of an invention is evident to the meanest capacity, and consistent with experience; they are impertinent where they are not, for they then seek to choke you with their rubbish, advocating, upon incorrect data, the advantages of long forgotten and disused plans. There are too many instances of the insufficiency of these alone, to carry conviction. Who will believe them, if not in accordance with well known principles-the operation of laws, however modified in application, the same in practice? Prejudice must be removed, by leaving it no hold to cling to; that, if objections be then urged, they can be attributed only to sources which must render them unimportant.