ON MAEINE BOILEKS. 185

“ Mr. Jack did not presume to state con-fidently that distilled water is really itself theactive destroyer of iron boilers; but, from theobservations that have now been referred to,and the information he has been enabled toobtain, he thinks there is sufficient evidencethat distilled water is, if not the sole cause, atleast an active agent in producing the corro-sive effects that have been described. If thissuggestion should lead to the remedy of theevils that have been experienced where distilledwater alone has been used, another difficultywill have been overcome towards the completeintroduction of ‘ surface condensers.’ ”

This paper elicited a discussion usual on theseoccasions, of which the following is a portion :

Mr. D. Hollo observed “ with regard to theboilers at the sugar refinery that had beenreferred to, the corrosion could not, he thought,have been caused in that case by the presenceof brass particles in the water; for the steampassed only between the two cast iron platesof the evaporating pans, and when condensedreturned again to the boiler, without coming incontact with any brass at all in the apparatus,the leakage being made up by the addition ofa little fresh water. There were four boilersall working together, two fed with the distilledwater returned from the evaporating pans andtwo with fresh water: the two latter at thetime of examination were found in perfectcondition after four years’ work, having only alarge deposit or scale of lime over the surfaceof the iron ; while the other twm fed with thedistilled water, after the same time of working,had become quite unsafe from corrosion and hadto he very extensively repaired. They hadtried various remedies for the evil: suspending

zinc plates in the boilers, but with what resulthad not yet been ascertained; cast iron pipesinstead of copper pipes for conveying the steam;and tinned tubes, zinc, and galvanised irontubes in the condensers, instead of brass.Block tin tubes had also been tried, but werefound not to have strength enough to supporttheir own weight when placed horizontally.All these trials, therefore, still left the questionof the cause of corrosion undecided: but hethought it could not be the action of copper,because the analysis that had been made of thedeposit found in the boilers using surface con-densers showed a very small proportion of cop-per, the main metallic ingredient being iron, andthere was not sufficient copper collected from theboilers in the voyage of a steamship to accountfor such an extent of corrosion as was met with.Where much grease, however, was used in theengine he had seen the inside of a boiler pre-sent an appearance which, bethought, renderedit just possible that the fatty matter or acidscontained in the grease had something to dowith deteriorating the quality of the waterand causing its corrosive action.

He further explained that, in all the vesselsthey had fitted up with surface condensers, morethan twenty-five in number, the boilers hadbeen tubular boilers, all with iron tubes, ex-cepting only one or two cases where brassboiler tubes were used; and in all cases thecondenser tubes were brass. With regard tosteel boiler tubes, he had seen them tried, andwith no better results than the iron tubes;indeed, in some instances, they becamecorroded rather quicker than iron tubes, butwhether that was owing to the additionalcarbon contained in the steel he could not say.

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