explosive mixture, the movement of a valve cuts off the supply, and brings
the igniting arrangement into action. The pressure produced by the
explosion acting upon the piston makes it complete its stroke, when the
exhaust valve opens exactly as in the steam engine. The Lenoir and Hugon
engines, the earlier forms of this type, were double acting, receiving two
impulses for every revolution of the crank, the impulse differing from
that in a high pressure steam engine in commencing at half stroke.

The Lenoir igniting arrangement was complicated and troublesome. I have it
upon the table; the mixture was ignited at the proper time by the electric
spark produced from a primary battery and Ruhmkorff coil.

The Hugon engine was an advance in this respect, using a flame ignited,
and securing greater certainty of action in a comparatively simple manner.

It is really a modification of Barnett's lighting cock described in his
patent of 1838.

Other difficulties were found in using these engines; the pistons became
exceedingly hot. In the case of the Lenoir larger engines, it sometimes
became red hot, and caused complete ruin of the cylinder by scoring and
cutting up. Hugon to prevent this injected some water.

In the all important question of economy, these engines were found
grievously wanting, Lenoir consuming 95 cubic feet per I.H.P. per hour;
Hugon consuming 85 cubic feet per I.H.P. per hour.

The surviving engines of this type are only used for very small powers,
from one to four man power, or 1/8 to 1/2 horse, the most widely known of
this kind being the "Bischoff," which is very largely used; its