Miscellaneous Implements Bxhibited at WanvicJc. 531 
while the exhaust valve and the valve for the mixture of air and 
gas consist of one double action valve, with a mushroom head 
and piston. The first part of the rise opens the mushroom for 
the exhaust passage, and in the third portion the passage for the 
explosive mixture is opened. This ai’rangement is adopted for 
the smaller sizes of engines up to 20 horse-power ; beyond that 
power each valve is worked by its own cam and lever. The 
illustration (fig. 3) shows one of the smaller engines. 
The larger engine is fitted with a self-starting appliance, 
consisting of a vessel fixed close to the engine, into which air is 
pumped at a pressure of about 40 lb. by means of a hand pump. 
C 
Fio. 3.— Fielding <fc Platt’s Gas Engine. 
When the engine is about to be started, the gas supply valve 
to the cylinder is opened, the gas displacing the air contained 
in the cylinder. The cock on the air receiver is then opened 
and the compressed air admitted, which, mixing with the gas, 
forms an explosive mixture. 
The firing is effected by means of an ignition tube heated in 
the usual way by a Bunsen burner. 
The Campbell Gas Engine Co., Halifax (Stand 258). In these 
engines a departure is made from the Otto Cycle; three were 
exhibited, of 1 horse-power, 3 horse-power, and 6 horse-power 
respectively. They are designed so as to give an ignition at every 
revolution of the crank when required ; as a consequence, the 
m'laiiiiimnniiHiiniiuioii 
