CAUSE AND EFFECT OF INCRUSTATION. 177

S. S. “ Lancefield ” with about ten times thesurface which it had been customary to give tosuch apparatus; but the results, as stated at arecent meeting, were so much at variance withmy understanding of the ordinary theory, thatI think a statement of the facts will helpothers to a clearer knowledge of the matter.

“ The vessel sailed from Glasgow about noonevery Thursday for the Hebrides , lay in oneof the lochs there from Saturday evening tillMonday morning, and arrived again in Glasgow on Wednesday, to recommence on Thursday asimilar voyage. The steam was up or at handall the voyage : about fifteen stops, of two orthree hours each, were made each week, duringwhich time the boiler was supplied with feedby a Giffard’s injector, but little or no blow-off.While steaming, however, the quantity of watercontinually discharged through the regeneratorwas so great that the glass hydrometer usedfor ascertaining the density showed very littledifference between the sea and the boiler water.The boiler was worked in this manner for aboutfour weeks, and then examined; when, insteadof being found, as I expected, clean, with littleor no scale or deposit, the coating was muchthicker than usual, but soft, very much likenewly-made mortar, not difficult, before gettingdried, to scrape off at all accessible places, butwhich when dry was nearly as difficult ofremoval as the ordinary compact scale.

“ During one of the voyages, when I waspersonally directing the experiment, and hadfor some time been keeping the greatest amountof feed on the boiler which the engine couldsupply, I observed the water in the gauge glassgot muddy, but did not then discover the cause.About two years before this I found the same

soft limy deposit in the S. S. ‘ Isleman’s ’boiler, when trying similar experiments on thesame station; but as I had disregarded the‘ Isleman’s ’ experience, and did not thenknow the experience of others, the ‘Lance-field’s ’ regenerator was continued, but withlesser quantities of feed and discharge, for'about six months, when the tubes of theapparatus giving way, it was discontinued. Iwas fortunately saved further trouble, and theexpense of repairing it, by discovering in theAnnales des Mines for 1854, an interestingpaper by M. Couste, ‘ On the Incrustations ofBoilers.’ He there shows that the sulphate oflime can be deposited by heat alone, withoutany evaporation, and that at a temperature of124 deg. Cent., or two atmospheres of pressure,sea water in its natural state is very near thepoint of saturation. As the ‘ Lancefield’s ’boiler was loaded to nearly 40 lbs. of absolutepressure, and worked generally at about twoatmospheres, or 255 deg. Fahr., or about thepoint of saturation of the lime, it is clear thatthe greater the amount of sea water suppliedto the boiler, the greater would be the quantityof lime deposited in it. And although therewas a constant discharge from the surface by aconical tube, only some of the deposited matter—that which had not attached itself to theboiler—could be so discharged. If this be notthe true explanation of the great deposit in the‘ Lancefield’s ’ boiler, of the difficulty of work-ing hollers with sea water at higher pressures,and of the ordinary experience that boilers arecleaner when worked at a greater density, itwill remain for others to explain it.

“ M. Couste s experiments, however, appearto me to be conclusive. He suggests a method

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