NO. 2. ON BOILER INCRUSTATIONS. Without entering into a history of all that has been said and written on the incrustation of boilers and its prevention, ! we will limit ourselves to a summary of the late conclusive ! experiments conducted by Arthur Morin and H. Tresca, which give a clear idea of the loss of fuel caused by " dirty" boilers. These gentlemen have practically demonstrated thai-, in a clean boiler, in good working order, they actually evaporated 441 lbs. of water by the combustion of 51'81 lbs. of coal, whereas, this same boiler, after having been run for some time, and becoming coated, only produced 299'88 lbs. of steam by the consumption of 76'51 lbs. of the same kind of coal In the first case, 18'74 lbs. of water were converted into steam I by the combustion of 2'205 lbs of coal; in the second, only 8'531bs.; this being equivalent to a loss of 52 per cent. In the ordinary apparatus for distilling salt water on board of ships at sea, the same quantity of coal which will evaporate 600 lbs. of water, when the kettles have been nowly cleansed, will, in a short while, only produce 200 lbs. of distilled water; being a waste of two-thirds of the fuel, attributable to incrustation alone. All impure waters, or such as hold in solution chloride of sodium (common salt), sulphate of soda, carbonate of soda, carbonate of lime, or carbonate of magnesia, protoxide of iron, silica, chloride of magnesium, sulphate of magnesia, or sulphate of lime (and few waters are completely free from one or other of these substances), will, inevitably, after a longer or shorter period of time, form solid deposits on the sides and bottoms of the vessels in which they are heated. The effect of this phenomenon is a constantly increasing waste of fuel by the gradual obstruction occasioned to the transmission of heat, from the coal to the water jn the boiler, through a bad conducting medium. The danger of burning the boiler-plates is well known to be great whenever incrustation is allowed to progress to any considerable extent, beside which, some of the impurities are sure, sooner or later, to find their way into the slide-valves and cylinders, where their action is eminently prejudicial to the durability of these parts of the engine. The genius of inventors has been, for some time past, tasked to a remarkable degree, in order to discover some means of preventing incrustation in steam boilers. Chemical science, natural philosophy, and mechanics have, each of them, contributed many supposed " panaceas" for the attainment pt this very important purpose, but we must humbly confess (regardless of the anathemas of said inventors), that we know of no universal remedy applicable in all cases, neither do we believe that such a one will be discovered. A good chemist, knowing the impurities of any particular water, may, in some cases, be able to indicate to the engineer a chemical agent which will precipitate a portion of these impurities in a special feed-water tank ; but in many instances the chemicals used will end by acting deleteriously on the iron or copper of the boiler or on the rubbing surfaces of the engine, so that they must always be applied with the utmost caution. Heating the feed water by means of the exhaust steam is in most cases quite inefficient, the temperature attained being too low to be serviceable, except in the case of bicarbonate of lime. Successful precipitation'at temperatures higher than boiling-water, needs the employment of accessory high-pressure boilers, which in their turn become incrustated, and waste as much fuel as the original boiler. Blowing off is the usual mode of relief resorted to by our present engineers; how unsatisfactory this has proved itself to be, we attempted to show in a previous article. Surface condensers, as at present manufactured, are too expensive and objectionable from many other causes. Mashed potatoes, oxalic acid, carbonate of potash or soda, nitric, muriatic, or acetic acids, sulphate of alumina, and one hundred or more " patented " and " unpatented " anti-incms-tators, may each of them individually find their useful application in special cases; but, as we have before remarked, none of them will answer for all sorts of boilers nor for all kinds of water. Which method is to be preferred must be left to the judgment and science of the competent engineer, who ought to know, the least objectionable remedy to be applied in, his own particular case. Much valuable information in regard to the present subject will be found by looking through the back volumes of the SCIENTIFIC AMERICAN. We conclude by the following " truisms," which are, unfortunately, too seldom sufficiently attended to, although of the highest importance in their bearing on the saving of fuel. 1. Use as pure water as your locality affords. 2. Clean and scrape your boilers as often as yo\i possibly can 3. " Blow off " without excess. 4. In case of salt or brackish waters, never use steam oi over 90 lbs. pressure to the square inch. 5. In case of sulphate of lime waters, never use steam of over 70 lbs. pressure. 6. In case of water holding carbonate of lime in solution, pass it through a feed-water heater made hot by exhaust steam or by waste heat. 7. In case of muddy waters, use large feed-water cisterns or reservoirs, on the bottom of which the suspended earthy matters will soon form a soft deposit, when the surface water can be drawn off for use. 135 8. Favor tlie invention of a compact, simple, cheap, and efficient surface condenser or its substitute, more than you do the quack " nostrums " of most anti-incrustators