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MODERN STEAM PRACTICE.

ioo lbs. steam pressure is used, boilers of the locomotive type aredecidedly the best, and they can be made of Steel, thus tendingmaterially to increase the carrying power for cargo by lightening theboiler. The same dass is largely used for steam-launches, havingthe whole of the machinery fitted thereto.

Torpedo boats are now fitted with the locomotive type of boiler,carrying a working pressure of about 120 lbs. per square inch. Thedraught is forced by a fan blast. The evaporation in these boilersper lb. of coal seems to be about 7 lbs., and the evaporation per hourper square foot of heating surface varies from 11 to 18 lbs. The coalconsumed per hour per square foot of grate varies from 50 to 100 lbs.

The haystack boiler, originally introduced in Clyde river practice,is well suited for vessels of light draft. The shell is cylindricalwith a dome-shaped top. The tubes are placed vertically, with thefurnaces beneath and around the sides.

PROPORTIONS FOR MARINE BOILERS.

When a number of boilers are to be designed of various sizes, itwill facilitate the designer if he fixes on the scale to be universallyadopted, and get the drawing-paper prepared with light lines, ruledin 2-inch squares, according to the scale determined on, these squarescorresponding to the pitch of the rivets, or 2 inches between centreand centre. It is by far the cheapest and best arrangement wherethe front and the sides are worked square at the corners, the backat the top and the bottom being rounded, as in many instancesthis requires to be done to fit the midship sections of the vessel.Boilers so designed, and drawn on ruled paper, greatly assist thedraughtsman in getting up the working drawings for the Work-shop.

After making a rough sketch of a boiler, we know about thelength, breadth, and the height required, and commencing on theside of a square, we lay off the length, breadth, and the height perscale; thus the configuration of the boiler is represented by so manysquares; the length, breadth, and the height should always be evendimensions, and there is nothing to prevent all boilers being soconstructed. We may now set out the plating, taking the centre ofthe squares as the edges of the plates, wherever we arrange the joints,breaking bond where required. It is evident that the plates must bealways of even dimensions. Each plate will contain as many rivets,of the universal pitch of 2 inches, as there are squares; thus by