276 



GASSELL'S POPTJLAE GAEDENING. 



High-preasure valves should always be used where 

 toUers are coupled together, in aU mains, and 

 wherever it may he thought desirable to effectually 

 shut hack the water in case of break-down or acci- 

 dent. The three valves (Figs. 52, 53, 54) manu- 

 factured by Foster and Pearson, of Beeston, to which 

 the Horticultural Society's medal has been awarded, 

 are admirably suited to this purpose, as they answer 

 the two-fold purpose of valve and stop-tap. 



Valves are sometimes placed in front of H-pieces 

 (Kg. 85) when a flow and return pipe run through 



sented as being capable of doing the work. Then, 

 were two forms, one more simple than the other, 

 presented for our approval, we should not go far 

 wrong in choosing the simplest form, affording the 

 largest surface for the fuel to act upon in a direct 

 manner. 



Makers of boUers often prejudice themselves, and 

 disappoint the public, by specifying the quantity of 

 piping their boUers will heat when everything is 

 fresh, clean, and new, the interior free from incrusta- 

 tion, and the flues clear of dust. Driving, however, 

 does not mean economy of fuel, and, as aU practical 

 men are anxious to obtain an apparatus that will do 

 the greatest amount of work at the smallest outlay 

 for fuel, or for repairs in case of accident, a boiler 

 capable of heating fifty per cent, more piping than is 



Pis 55.— H-piece with Valvei. 



several compartments, say a, b, c (Fig. 56); by 

 placing the castings, say at o, a can be heated by 



Pig. 56. 



O P 



-Heating Compartments separately. 



shutting the valves, a I, while b and c remain cold. 

 By opening them at o, and closing them at p, A and 

 B can be heated, while c remains cold ; and by open- 

 ing all the valves, the three sections will be heated. 

 H-pieces are often made with valves at c, but with an 

 air pipe at the extreme limit of c, these are of no 

 practical value. 



Boilers. — The number of these before the public 

 is now very great, and, at first sight, alinost for- 

 midable ; but when classified and divided into three 

 or four sections, to which nearly all of them belong, 

 the diiEculty in- choosing a boiler for any special, 

 purpose is not so great as many imagine. 



The power of a boiler depends upon the area of 

 heating surface, and the amount of heat given out 

 depends upon the position of that surface, and the 

 way in which a boiler is stoked. If every square 

 foot of effective heating surface in a boiler is equal 

 to the heating of forty to fifty feet of four-inch 

 piping, and fifty to sixty feet of three-inch, it is easy 

 to decide upon the boiler capable of doing the work, 

 provided always that we take off thirty per cent, of 

 the manufacturer's calculation, and take two boilers 

 to heat, say, one thousand feet, when one is rcpre- 



rig. 57.— Plain Saddle Boiler. 



likely to be attached should always be selected, as it 

 wiU be found the cheapest in the end. 



The following table gives the maximum quantity 

 of pipe which a boiler will heat, supposing th& best 

 fuel only be used ; every square foot of boiler ex- 

 posed to the direct action of the fire being equal to 

 three square feet of flue surface : — 



A small apparatus ought always to have more sur- 

 face of boiler in proportion to the length of pipe 

 than a larger one, as the fire is less intense, and bums 

 to less advantage, ia a small than in a larger furnace. 



The Saddle Boiler is too well known to require 

 description. The plain saddle (Fig. 57) is the type 

 of a great number of boilers, which cannot easily be 

 beaten. It is made in cast and wrought iron, welded 

 or riveted. "Wrought-iron boilers, although more 

 subject to incrustation, are generally chosen in pre- 

 ference to cast, and when well set over a fire-place 

 composed of fire-bricks, and properly stoked, they 

 are sure to give satisfaction. An improved form of 



