vantage of independence of a local-supply company and of portability.

Most manufacturers charge extra for exhaust pipe and silencing-box, the cost varying from £1 10s. to £9, say $7 to $45; also for foundation bolts, from 8s. to I IOS., say $2 to $7.50, if they be necessary. spects the costs are inclusive of all necessary parts.

In other re

The weight of complete portable oil-engines, with tanks and carriages, runs about the same as portable steam-engines of equal power.

CHAPTER XXXII.

THE VAPOUR OR GASOLINE ENGINE.

A FORM of motor known as a "gasoline" engine is finding extensive adoption in America, which does not appear to possess some of the chief merits of the genuine oil-engines described in the previous chapter, especially as regards the use by the latter of low-grade and safe mineral oil. On the contrary, these gasoline machines make use of a highly volatile liquid of only 74° test, costing about 10 cents a gallon in barrels. If such material is used at all, it should be stored in some safe place quite outside any buildings, and a supply brought by pipe to the engine, which is fitted with an 66 evaporator" or chamber in which the liquid may safely vaporize and through which the cold air is drawn to the cylinder. The resulting mixture is fired by an ignitiontube, much as a gas-engine does, the governor acting upon a throttle on the inlet-pipe, and the tube being heated by a jet of the "gasoline" underneath it.

The electric spark is sometimes applied for the purpose of ignition where the presence of a "gasoline" burner is objectionable. In other respects the machine is similar to a gas-engine and employs a water circulation of a similar character. It is claimed for these engines that they will run for ten hours on a consumption of about one gallon of gasoline per horse-power, or about one cent per horse-power per hour. This is no better than can be accomplished with a safer material, and the dangers attendant upon the use of this system are illustrated by the regulations of a wellknown fire-insurance office with reference to them. Per

mission is given for the use of the engine in an insured building "only under the following restrictions and conditions to be observed by the assured, viz.: That at no time shall there be to exceed one gallon of gasoline to be contained in metal reservoir within said building or additions, free from leak and away from artificial light or heat. The reservoir to be filled and the gasoline handled by daylight only. The supply-tank to be of iron and located outside of building and under ground, and to hold not to exceed two barrels."

Notwithstanding, a large number of these engines are now at work in many small industries throughout the States, especially in operating elevators and printing presses. Their cost and dimensions are about as follows:

The Naphtha Engine. This apparatus is a prime motor, deriving its force from the use of the lightest form of refined petroleum, and has been found a very handy little apparatus for driving launches. Strictly speaking, it is no more than a condensing steam-engine, inasmuch as the naphtha is used in place of water, and is turned into an expanded volume of vapour by the use of heat. The fire is, in these launches, also fed by the use of a portion of the same liquid, the objects attained being the use of but one

material on board the boat, very rapid raising and lowering of pressure, and condensation by a passage of the exhausted vapour in a copper coil, or tube, in contact with the seawater. Equally good results may be attained in driving. launches by the use of the heavier oils in the oil-engines now made in marine forms by Priestman, Daimler, and others. For the exclusive purpose of launch-driving the apparatus is good and has a future, but not so for land purposes. The vaporous liquid is highly inflammable, and its carriage is prohibited in certain countries and upon the best lines of vessels.

The vapour or gasoline system cannot be recommended as a motive power in comparison with the oil-engine, using oils of a low grade with complete safety.

THIS heat-engine was, when introduced in 1820 by Sterling, trumpeted as the future rival of steam, and has continued to be spasmodically vitalized by one or other of the ingenious inventors who have spent their energies in trying to overcome its inherent defects.

The apparatus is based upon the expansion of common air under heat, its alternate contraction and expansion being effected by its transference to and from a heated chamber.

In the work of driving the piston of an engine, however, the heat contained in air is so rapidly parted with that all the efforts of the various makers of these machines have not succeeded in placing engines of any serious power upon the market.

The Rider hot-air engine is a neat form of the apparatus, designed chiefly for domestic pumping duties, and others have been made by Bailey, Buckett, Tyler, and Robinson, but without much degree of success, except for the small powers and duties above-named.

In such a connection, however, their use is highly economical and successful, there being in use, it is said, upwards of ten thousand of the Rider type alone and some six thousand of that known as the Ericsson.

These little machines can use coal-preferably anthracite -coke, wood, gas, oil, or gasoline as fuel, and can be attended by any unskilled person, domestic servants having many of them in charge. For the special purpose of domestic pumping, up to 3,000 gallons per day, the hot-air