Exhibited at the Nottiivjham Mcetinrj. 
95 
type as Spiel's, and it was only after tliey had practically per- 
fected this machine that they discovered its commercial valueless- 
ness. The lesson, however, was not lost, and they have now 
succeeded in doing with common petroleum all that they were 
previously able to accomplish with a more volatile fluid. 
For the engine of Messrs. Priestman the ordinary kerosine or 
rock oil is used, which, having a flashing point of from 75° up to 
150° Fahr., is free from the objections that attach to " petroleum " 
as defined in the Petroleum Act of 1879 — i.e. with a flashing 
point of less than 73° Fahr. (as to which alone Local Authorities 
have the power to enforce regulations). The distinction between 
the two classes of motors, petroleum oil motors and petroleum 
spirit motors, which are together included in the generic term 
" petroleum engine," is important to be observed. Mr. Boverton 
Kedwood, the acknowledged authority on the subject, observes 
in a recent memorandum that " the two liquids thus employed 
"differ essentially in regard to inflammability; petroleum spirit 
" taking fire readily at common temperatures, while petroleum oil 
" requires to be heated to about 120° Fahr., or higher, before it will 
" ignite. • . . Petroleum oil is commonly known in the trade as 
*' ' petroleum,' while the more volatile product is commercially 
" designated in this country ' petroleum spirit ' or ' benzoline.' " 
The cycle of operations in the Petroleum Engine is much 
the same as that of the well-known " Otto " Gas Engine, there 
being one explosion of mingled oil and air in the cylinder for 
every two revolutions. 
A pump at the side of the engine forces air into an oil-reservoir, at a 
pressure of a few pounds per square inch. The compressed air, escaping 
from a small jet, carries with it oil, in the form of very fine spray, which, 
first, issues into a jacketed chamber heated by the Exhaust, consisting of 
the products of combustion. The mingled air and oil is there raised to a 
temperature of about 300°, and then drawn, with more air, into the cylinder, 
where, after being compressed by the return strolie of the piston, it is ex- 
ploded. Firing is accomplished by the electric spark, and, at the end of the 
working stroke, the exhaust valve opens and the products of combustion are 
discharged into the air. The speed of the engine is regulated by a governor 
which controls both the flow of oil and the amount of atmospheric air 
which is mixed with it. 
The crux of the oil-engine is how to obtain perfect com- 
bustion, failing which the cylinder is soon fouled by a de- 
position of soot. It would be difiicult without illustration, and 
indeed hardly fair to the inventors, minutely to describe the 
clever devices which, after a long series of experiments, have 
been adopted by them for the purpose of mixing air and oil in 
predetermined proportions. Suffice it to say, these are beautiful 
examples of ingenuity and perseverance applied to the solution 
of a problem of unusual difficulty. 
