262 Mr. Johnston's Description of a Steam Boiler. 



Mr. Cockey oxliibited and described a model of Smart's steam-boat 

 paddlo float. 



Mr. James Johnston then gave a description of a seven horse power 

 boiler, constructed according to his patent plan, so as to prevent the 

 formation of deposits on the interior of the boiler. 



The boiler, properly speaking, consists of two parts, viz.: — The 

 furnace, and the body of tho boiler. 



The furnace is placed on the front and outside of the boiler; tho 

 sides and roof of it are made of a double casing of sheet iron, the iron 

 of each casing being one-eighth part of an inch thick ; the water space 

 between the casings is a quarter of an inch wide, and the casings are 

 bolted to one another every two-and-a-half inches. The sides of the 

 furnace are perpendicular — the roof is sloped like the roof of a house, 

 each half of the roof being set at an angle of forty-five degrees on 

 the sides of the furnace. The water space of the furnace has three 

 openings or communications with the body of the boiler ; of these 

 communications there is one at the lower part of each side of the 

 furnace, the other one is at the ridge of the roof of the furnace. In 

 consequence of this arrangement, there is constantly a powerful 

 current of water circulating up the sides, and over and along the roof 

 of the furnace; it is this current of water which prevents the deposits 

 of salt and other substances. 



The body of the boiler is divided into seven chambers or flues, 

 which communicate at one end with the furnace ; at the other end 

 they are each provided with a separate chimney, which communicates 

 with the funnel. Each of those chambers measures from top to 

 bottom two feet nine inches, from furnace to chimney two feet, width 

 two inches. Between each chamber there is a water space of a 

 quarter of an inch in width. The latter are the spaces in which the 

 ascending current of water is created in consequence of the action of 

 the heat which is supplied from the seven chambers. 



At each side, in the body of the boiler, there is a large water space 

 through which the currents of water descend. The fire is not allowed 

 to act on those descending water spaces, for, if the fire were allowed 

 to do so, the velocity of the current would be checked, and the boiler 

 injured. 



The entrances from the seven chambers into the chimneys, are at 

 the bottom, or lower part of the chambers. In consequence of this 

 a saving of fuel is effected, as the products of combustion are by this 

 means retained in tho chambers until all the available heat has been 

 absorbed by the water. 



Note. — This boiler is at present working on board the " Alert" 

 steamer, at the West Quay, Greenock. 



