SMOKE BURNING.

Notwithstanding the number of smoke-burning furnaces which have at different times been introduced, it cannot be said that any plan has yet been contrived which so far satisfies the conditions of the problem as to command general recognition of its eligibility, or to lead to its general adoption. These plans operate either on the principle of admitting air above the fuel to burn the smoke-which has the radical defect that the production of smoke in ordinary furnaces is variable, whereas the admission of air is constant, so that either too much or too little will generally enter-or on the principle of passing the smoke over the incandescent fuel, or through red-hot pipes or fire-brick passages—which though it will diminish the smoke, will rarely wholly prevent it; while the apparatus required is generally cumbrous. A proper smoke-burning furnace should obviate the smoke effectually; and it should be of simple construction, and be exempt from the objection of admitting too much or too little air to burn the smoke. In steam vessels it is most desirable that some proper species of firing apparatus should be employed; as the labour and difficulty of firing large furnaces at sea, especially in hot climates, is very great.

It has already been stated that the tubular marine boiler introduced by me in 1838 and patented in the same year was fitted with smokeless furnaces, the gases being generated in retorts placed in suitable chambers

D

lined with fire-brick, and communicating with the furnaces by short necks, through which the heat ascended. In 1839 I introduced smokeless furnaces into different steamers, in which the arrangements had to vary to suit existing boilers; and in some cases I caused the smoke to pass over the incandescent fuel, in other cases to pass through heated fire-tile channels, and in other cases again two adjacent furnaces were fired alternately, and the smoke from the one passed through the glowing embers of the other. All these expedients, however, are imperfect; and no species of smokeless furnace has yet been contrived of such conspicuous eligibility, as to ensure its general adoption. I believe that a good smokeless furnace and a good self-feeding furnace will come together.

GIFFARD'S INJECTOR FOR FEEDING BOILERS.

This is an instrument for forcing water into boilers by means of a jet of steam proceeding from the boiler itself; and its action is somewhat paradoxical, as it is capable of sending water into a boiler which has a considerably greater pressure of steam than that which the steam comes from. The feed water must not be hotter than 120° Fahrenheit, to enable the injector to act; for one condition of its action is that the steam shall be condensed; and this circumstance appears likely to restrict the use of the instrument— unless suitably modified-as the feed water should certainly enter the boiler at the boiling point, to which it should be raised by heat otherwise going to

TO BOILER

waste.

In this injector a stream of steam entering from the boiler at the highest nozzle, represented in fig. 51, is directed upon water entering the instrument through the nozzle next below; and as the whole power of the issuing steam has been expended in giving momentum to its own particles, that power, which cannot be destroyed, reappears as increased pressure, and forces the water into the boiler.* Should the water be shut off from the boiler as not being required, then it escapes, by the nozzle next beneath, through a loaded valve of the usual kind; and the valve at the bottom of the instrument prevents the return of the water when the instrument is not in use. The advantage of this apparatus is that it gets rid of the feed pump with its valves, which have been a source of constant trouble in engines working at a high speed. But unless it can be so modified as to send the feed water into the boiler at the boiling point to which it will be heated by the waste heat of the engine, I do not see how this injector can be retained as a main feeding instrument, though it will always be valuable as an auxiliary.

The sizes and prices of different injectors, proper for sending any desired number of gallons of water into a boiler in the hour, are given in the following table:

* The injector is virtually a hydraulic ram reversed, in which the small quantity of water in the steam, moving at a high velocity, forces a larger quantity of water against a lower head.