76 
may be more than is required at ordinary times, but occasions may 
arise when more power would be desired. 
There are many methods by which gasoline is fed into the cylinders 
of these engines. The better engines have a pump by which the gas- 
oline is forced into the cylinder. The ignition is accomplished by one 
of two methods — either by an ignition burner on the outside of the 
cylinder which communicates heat to a platinum point which explodes 
the gasoline vapor, or by an electric spark from an induction coil 
which is connected with numerous dry batteries. The cooling tank 
used with these engines for the purpose of keeping the cylinder moist 
and cool is usually from 12 to 14 inches in diameter. This size is 
intended for stationary engines, where the water can not be renewed 
frequently. In spra34ng, however, the water can be renewed ever}^ 
few hours if necessar}^; and therefore the tanks can be built as small 
as 6 inches in diameter, which will make a considerable reduction in 
the weight of the machinery. 
Purchasers are always given full instructions in regard to the care 
and running of these engines, so that one with comparatively little 
mechanical ingenuity has ver}^ little trouble. The greatest source of 
difficult}^ is with the electric current. The insulations often become 
imperfect or the sparking points become dirt}^ and fail to produce a 
spark. B}^ carefully testing the current and keeping these points 
clean practically all of the trouble is avoided. 
It is preferable to place the engine at the rear end of the frame and 
the pump as near the engine as possible. There are two types of spray- 
ing pumps which ma}^ be used for this purpose — the triplex pump, 
which consists of three vertical plungers, and the straight horizontal 
double-acting force pump. Either of these pumps will be found to 
answer to the conditions required for these outlits, but the horizontal 
pump is more commonl}^ used. The pumps should be so manufactured 
that all of the parts are accessible and the brass lining easil}^ removed. 
The working parts should be made of brass or bronze. A large air 
chamber is essential, as well as a pressure gauge. It is absolutel}^ 
necessary that a relief valve be attached to the pump, so that when 
the stopcocks on the bamboo extension are closed the engine will not 
have to be stopped, but at a certain pressure the spraj^ing liquid Avill 
be returned to the tank. 
In sections of the countrj" where irrigation is practiced it has been 
found that the most effective method of filling the tank is to have 
another pump which can be attached to the engine, by which water 
can be pumped from an irrigating ditch into the tank. This pump 
should belong to the t3'pe known as "low-down pumps," which 
deliver large quantities of water at low pressure. The suction hose 
should be 2 or 3 inches in diameter and the end which is put into the 
irrigating ditch should be w T screened. There is usually some 
