806 REPORT— 1886. 



supplied to the furnace unquestionably is a distinct saving, but tbe writer is of the 

 opinion the cost of fitting an arrangement for such purpose when altering a boiler 

 to forced draught will exceed the saving gained. When new boilers are supplied 

 the increased cost will, however, probably be only small. 



The application of forced draught to the Marmora proved so economical that 

 it was decided when ordering the s.s. Stella, a steamer of 3,800 tons, having triple 

 expansion engines, to apply forced draught to the boilers, which are subject to a 

 pressure of 143 lbs. 



Messrs. Wyllie & Morison's patent system was applied and the results have 

 proved most successful. 



The writer believes the Mannora was the first instance in which forced draught 

 on the ' closed ash-pit ' system was applied to a boiler which had been for some 

 time in use under the ordinary conditions of natural draught, and ran the same for 

 eleven consecutive voyages with considerable success, and he likewise believes the 

 Stella is the first instance of a triple expansion engine having the boilers fitted with 

 forced draughts. 



5. The Domestic Motor. By Henry Dayet, M.Inst.C.E. 



The Domestic Motor is really a steam engine working with negative pressure 

 only, and therefore explosion is impossible. It is automatic in all its functions, 

 and may therefore be left without an attendant for a considerable length of time. 



There are two forms of the motor — one in which the engine and boiler are 

 on one casting, the other in which the boiler is separate and made to contain from 

 six to eight hours' supply of coke. This latter form has been specially designed 

 for electric lighting purposes. 



The engine part of the motor consists of a cylinder, piston and slide valve, 

 similar to those of an ordinary steam engine. 



The exhaust from the cylinder is discharged into a surface condenser consisting 

 of a series of wrought-iron tubes. The condensed steam and air from the surface 

 condenser are withdrawn by means of an extremely simple form of air-pump, 

 discharging into a small water pocket, from which the water again enters the 

 boiler, so that the water used for raising steam is used over and over again, thereby 

 preventing a deposit in the boiler. 



Any waste arising from leakage is automatically supplied from the condenser. 



All the functions of the motor are automatic, except the firing, and the fire 

 in the separate boiler type only requires attention once in from six to eight hours. 

 The fuel used is gas coke. It has been found by careful experiments with the 

 motor that the consumption of coke is from 6 to 7 lbs. per brake horse-power per 

 hour in the self-contained type, and very much less in the separate boiler type. 

 In general construction it is very similar to the boiler sometimes used for heating 

 conservatories. The boiler contains a large vertical column of coke, which burns 

 at the bottom, the coke above falling down by its own weight. As the bottom 

 portion is burnt away, the weight of the column crushes the ashes through the 

 spaces between the fire-bars, and the combustion 13 thereby maintained con- 

 tinuous. The column of coke is made sufficiently large and sufficiently high to 

 keep up a constant rate of combustion for, say, six or eight hours. 



It will be interesting here to notice that the total efficiency of the heating 

 surface of the boiler is greater with this mode of firing than with any other. 

 It has generally been well known that the fire-box of a locomotive boiler 

 does by far the greater portion of the work in raising steam. The boiler under 

 notice has no heating surface, except that of the fire-box, but the fire-box is so 

 constructed that a great portion of the heat of the spent gases is trapped by the 

 green fuel which is approaching the condition of combustion in the fire-box. So 

 completely is the waste heat utilised that it is possible to put one's hand into the 

 top of the boiler and take out lumps of coke, even when the coke is nearly half 

 way down in the fuel space. 



The author has not had time to make careful quantitative experiments as to the 

 value of the heating surface and the economy of this kind of boiler, but he is con- 



