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"TAE MARINE REVIEW 33 T Fig.2. NEW TYPE OF MARINE FIRE TUBE BOILER. Fig.t. Heating surface of the heaters and of the sq. tL, UPPET VESSEL Go) ao ee i T0103) TOtAl Weatine' suriace oo ons ce ee 1162.5: ° RGRAEE GEO bo oe i es ap Woter smmice 3. 5 2 a Oe. 191.4 cu. ft. . Stew spacers: 5. yrs ia oe Wa Weight of the boiler, excluding uptakes and HHS eG ee eee ee 11.320 tons Weight of the fittings, brickwork, and grate WR ee a ee ae 307 ie Fotal weight of empty boiler... .....2....4.. 14.627" Total weight of the boiler with water at Horinal (eveb 6 ese es 19.410 © The saving. of weight and space in such a boiler, as com- pared with the Scotch type is evident. On one, side the weight of water is reduced because of the small water spaces, on the other side the suppression of the thick and large tube and shell-plates reduces by a considerable amount the weight of the metallic parts. This saving of weight is about 40 per cent for the metallic parts, and 60 per cent for the water, or in all about 50 per cent when comparison is made between a two-furnace boiler of this new type and a two-furnace sin- gle-ended Scotch boiler. This saving of space in the trans- verse sense is apparent, the breadth of the boiler under ex- amination being only a little greater than the breadth of its grate. In the above instance this saving may amount to about 4 ft. As to the length and the height no variation is to be found between the two types of boiler, a diminution of the height being, moreover, possible beyond a certain diameter of the corresponding tank boiler. If we now compare the new type with water tube types of the heavy class, we find no appreciable difference in weight per indicated horse- power under low forced draft--!4 in. water--and some advantage on greater draft--1 in. No weak part of this boiler is exposed to the direct action of the flame. As to its durability, its furnace is not inferior to that of a locomotive, of which large experience has been . made in the Italian navy. Moreover, an overheating of the furnace is very far from probable, as the space above is always full of water, owing to its position below the upper vessels. It is to be added, that" im case ot erttical contingencies, drawing the fires may be attempted in this. type of boiler. The composition of the boiler made up of. various vessels connected by simple tubes, allows free expan- sion. As to the heaters, they are cylindrical vessels of small diameter immersed in an atmosphere of gases, which can freely expand, and leakage occasioned by the overheating of the tube plate which receives the impact of the flames is not admissible. It may be concluded that this boiler is in better condition of resistance than the tank type under forced draft. As to the circulation of water, there is no doubt that, owing to the inclination of the inferior vessels, the steam tends to ascend towards thesfront end or top of these vessels, from which it is carried to the steam chamber along the corre- sponding circulation tubes. In these tubes, therefore, a current of steam takes place, and in consequence the. said tubes and the back ones are in the same conditions of the two arms of the well known U-shaped tube, on which experi- ments have been made to show the circulation in water tube boilers. A confirmation has been secured of the activity of the cir- culation by trials made on two models, one of which repre- sented to the scale, 1:10 the furnace compartment and the upper vessel with the circulation tubes, and the other one the heater and the said upper vessel with the respective connect- ing tubes. Although from these trials it was not possible to deduce. material results applicable to the boiler, yet they