3. By allowing the compressed air to enter the cylinder rapidly, through the quick manipulation of the stop-cock, which is closed again when the impulse is given and reopened at the corresponding period of the following cycle, this operation being repeated several times in order to impart sufficient speed to the motor;
4. By opening the gas-valve and finally closing the two valves of the compressed-air pipe.
The pipes and compressed-air reservoirs should be perfectly tight. The reservoirs should have a capacity in inverse ratio to the pressure under which they are placed, i.e., they increase in size as the pressure decreases. If, for example, the reservoirs should be operated normally at a pressure of 105 to 120 pounds per square inch, their capacity should be at least five or six times the volume of the engine-cylinder. If these reservoirs are charged by the engine itself, the pressure will always be less by 15 to 20 per cent. than that of the compression.
CHAPTER III
THE INSTALLATION OF AN ENGINE
In the preceding chapter the various structural details of an engine have been summarized and those arrangements indicated which, from a general standpoint, seem most commendable. No particular system has been described in order that this manual might be kept within proper limits. Moreover, the best-known writers, such as Hutton, Hiscox, Parsell and Weed, in America; Aimé Witz, in France; Dugald Clerk, Frederick Grover, and the late Bryan Donkin, in England; Güldner, Schottler, Thering, in Germany, have published very full descriptive works on the various types of engines.
We shall now consider the various methods which seem preferable in installing an engine. The directions to be given, the author believes, have not been hitherto published in any work, and are here formulated, after an experience of fifteen years, acquired in testing over 400 engines of all kinds, and in studying the methods of the leading gas-engine-building firms in the chief industrial centers of Europe and America.
Location.—The engine should be preferably located in a well-lighted place, accessible for inspection and maintenance, and should be kept entirely free from