_

EFFECT OF SUBFACE CONDENSATION ON MAEINE BOILERS. 181

better still to provide that the brine in theboiler shall never rise above double the strengthof ordinary sea water; and for this purposethe brine discharged should be equal to thefeed-water in volume .”

When treating this subject chemically, hestates: “ Thedeposition of carbonate of lime canbe prevented by dissolving sal ammoniac in thewater ; for that salt and the carbonate of limeare mutually decomposed, producing carbonateof ammonia and chloride of calcium, of whichboth are soluble in water, and the former isvolatile. The deposition of sulphate of limecan be prevented by dissolving carbonate ofsoda in the water ; the products being sulphateof soda and carbonate of lime, of which theformer is soluble, and the latter falls down ingrains, and does not adhere to the boiler.”

From these conclusions it is evident that“ blowing off ” has been considered, by theseveral authorities quoted, as the most efficientmeans for the prevention of deposit on theinternal surfaces of the marine boiler. Apartfrom this it is certain that the means adoptedwere put in practice after the water was in theboiler. Now a casual observer might coincidewith the conclusion that this way of dealingwith the matter in question was a reversemode, inasmuch that the water should bepurified before it entered the boiler. Onreflection this seems feasible, and doubtless theorigin of surface condensers.

In the present allusion to this last-mentionedportion of the marine engine, no notice will betaken of its arrangement or detail, but merelythe effect of the fluid, after passing throughthe surface condenser, on marine boilers.

As practical evidence in all matters of science

is of respective value, it has been deemedexpedient to introduce the following paper byJames Jack, Esq., of Liverpool, “ On the effectofSurface Condensers on Marine Boilers,” read atthe Institution of Mechanical Engineers , 18G3.

“As Mr. Jack’s firm has constructed and fixeda considerable number of surface condensersduring the last three or four years, and ascertain actions have been found to take placeon the tubes and plates of the boilers with thesesurface condensers, of such a character that thefull advantages of the use of distilled watercould not with impunity be obtained, it wasthe purpose of the present paper to give theparticulars of these effects. The effects pro-duced upon boilers where surface condensersare used must have been noticed by manyengineers, and the object of the paper wastherefore to induce discussion upon the subject,and elicit information which will enable thegreat advantages in the saving of fuel resultingfrom the employment of surface condensers tobe realised. As the boilers where surface con-densers are used are insidiously and rapidlyacted on, the danger of delay and of accidentfrom explosion is thereby greatly increased, ren-dering the question one of serious importance.

“ Surface condensation is a process by whichboth the sensible and the latent heat of thesteam are conveyed away; and, although theadoption of any new system is necessarily slow,Mr. Jack did not doubt but that surface con-densation will ultimately entirely supersedethe jet. There are evils however which requireremedying before surface condensation can beuniversally adopted for steam ships; not in thecondenser itself, but in the effects produced onthe boilers by distilled water or something

2 c