the use of worn-out or badly-constructed boilers. 3. Explosions arising from deficiency of water, incrustation, or corrosion. 4. Explosions arising from collapse. 5. Explosions arising from mis

management or ignorance.

28. In conclusion, all steam boilers should be regularly and thoroughly inspected, both internally and externally, by a competent and unbiased person.

As regards the working of traction engines, the directions given under the heading "Rules for Engine Drivers" will apply equally well to these as to most other types of engines. In addition, however, the driver of a traction engine should bear the following points in mind: (1) keep a good supply of water in the tank; (2) disconnect the traction gear, and start the engine under a moderate head of steam, say 25 lbs. pressure, to see that the pump and all working parts are in order; (3) carefully oil all bearings and grease the teeth of the various wheels; (4) for travelling get steam up to about 75 lbs. pressure; (5) when going down a hill the gauge glass should show 4 inches of water, when going up about 1 inch; (6) in going down hill lock the hind wheels of any vehicle being drawn; use the reversing lever both for shutting off steam and for checking the momentum of the engine by admitting steam to the reverse side of the pistons.

In working boilers a false level of water is sometimes shown in the water gauge from the partial or wholly closing of the bottom waterway by scale or scurf. The false water level in many cases may be accounted for through the condensation of the steam in the upper portion of the glass running down, and being prevented entering the boiler by the scale, it remains in the gauge glass and thus shows a false level. In the winter this condensation is, owing to the cold, of course more rapid, and especial care should therefore be taken in constantly testing the gauges to see that they are quite in order and perfectly clear.

We can also on large boilers recommend the use of a group of small pendent dead-weight safety valves in preference to a single large one, and these at a given pressure will require a less load, and at the same time will give a larger lip opening for the escape of steam.

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CHAPTER II.

CONSUMING SMOKE AND ECONOMISING FUEL.

THERE can be little doubt that several million tons of coal are annually wasted and disappear in the shape of smoke, in Great Britain alone, through imperfect combustion. It is a matter therefore of very great importance to steam users both on the score of economy and cleanliness. To make perfect combustion, it is well known that two equivalents of oxygen to one of carbon are needed, but all inventions or plans which have been tried up to the present fail either partially or entirely to effect this combination perfectly; hence the formation of carbonic oxide and consequent waste of fuel. A very large number of schemes have already been introduced, including mechanical stoking, improved furnace doors, improved fire-bars, and various methods of introducing air or steam into the combustion chamber. These certainly have effected considerable improvement, but much still remains to be done. The proper, or we may perhaps say the scientific, setting of steam boilers has much to do with their economical working.

The effective combustion of fuel may be said to depend chiefly on the following points: (1) construction of the furnace or fire-box; (2) the admission of the right quantity of air to the furnace; (3) the proper regulation of the draught; (4) regular and even firing. The admission of the right quantity of air to the furnace is a matter of great importance, but one often neglected. In the first place

care must be taken that sufficient air space between the fire-bars is allowed. It is, however, impossible to lay down an absolute rule as to what is the proper amount of air space to secure the most perfect combustion, as much depends on the nature of the fuel and the velocity of the draught through the flues, but roughly speaking an area of about 5 square inches for each square foot of grate surface should be provided. The air admitted through the firebars is not, as a rule, sufficient to procure efficient combustion, and air is usually admitted through the door or bridge of the furnace. We are of opinion that the air admitted from the bridge is the most efficacious in promoting combustion and preventing smoke. When coal in a furnace is in a state of combustion, it burns of the carbon it contains only an amount proportionate to the amount of oxygen that is brought in contact with it. In order to enable that combustion to take place the oxygen must be raised to a certain high temperature before it will combine with the fluid carbon. If it does not combine with the fluid carbon, it drives the latter before it, until it reaches the upper or outside air and disperses in the form of carbonic oxide or carbonic acid gas, as the case may be.

When the atmospheric air (or oxygen) is admitted to the furnace through the front bars of the grate, the velocity of the draught is usually such as to drive the atmospheric air straight through over the bed of the furnace, and before it has reached a degree of heat high enough to enable it to combine with the fluid carbon evolved from the coal it is driven over the fire, and consequently, instead of mixing or combining at a proper temperature with the fluid carbon, it drives the fluid carbon before it to the upper air unmixed and unconsumed. An important factor in the consumption of smoke is the correct arrangement of the chimney stack, so that from a steady and no

excessive flow of air an equal and steady combustion may be kept up in the boiler fire-grate.

Undoubtedly much can be effected in the consumption of smoke by means of furnaces constructed on improved principles. This was very successfully demonstrated some years back by Mr. E. B. Wilson, who constructed a number of furnaces in which, owing to their internal arrangements, the utmost intensity of heat could be obtained, and either concentrated within a limited space or diffused over a considerable area as may be found necessary. The furnace was fired on the principle laid down by Cutler many years ago, which consists in carrying on combustion inversely to the usual practice-that is, in burning the fuel from the upper surface downwards, instead of from the lower surface upwards. This plan with various modifications has since been tried, but with varying success. Wilson in his furnace dispensed with fire-bars and the ordinary door, and fed through an aperture in the top of the furnace, where air was also admitted. The coal was supplied in small pieces and fell on a curved inclined plane, on which it rested on a sloping bank until consumed. And more recently Livet's system of flues and boiler-setting has demonstrated successfully that the effective combustion of fuel depends also in a considerable degree on what may be called the proper or scientific setting of the boiler and the proportion and arrangement of flues.

The object of all smoke-consuming appliances is to improve or perfect the combustion of the superfluous carbon which is left unburnt either through the want of a sufficient supply of atmospheric air, or through the air not being raised to a sufficiently high temperature to allow it to mix intimately with the carburetted hydrogen, vapour of coal tar, and other gases that are thrown off by coal in a state of combustion. The hydrogen thrown off by the

heated coal is in all cases immediately fired or burnt, but should there not be a sufficient supply of heated atmosphere or oxygen to mix with the gases, the carbonic oxide, or smoke, is carried away by the draught up the chimney and into the atmosphere.

With the object of assimilating the supply of fuel to the quantity of air admitted to the combustion chamber, or of regulating the supply of air to the nature and quantity of fuel being consumed, a large number of appliances have been introduced, consisting of mechanical stokers, firebridges, fire-bars, furnace doors, inclined grates, improved boiler settings, &c. Although none of these may be called absolutely perfect under all conditions, undoubtedly great improvements in the combustion of fuel and consequent prevention of smoke have latterly been effected.

Much has been written on the best methods of consuming smoke by Williams, Prideaux, and others, and it is generally concluded "that the volume of air supplied to the combustion chamber must be neither greatly in excess nor greatly deficient of that necessary for perfect combustion," and we presume no one will attempt to contest this somewhat self-evident axiom. "If the air be seriously deficient, the fuel, if bituminous, is partly only distilled or sublimed into black smoke and tarry soot, the adherence of which to the boiler surfaces becomes a cause of further loss of effect. If the fuel be carbonaceous only, as coke, anthracite, &c., its gases are only oxidized to the state of carbonic oxide in part, and if the fuel be wood or peat the last result occurs with the distillation of various tarry and acid products (pyroligneous acid) highly destructive to iron boilers. If the volume of air be greatly in excess the heat of the furnace is reduced, and may be so to an extent to cause imperfect combustion, and a great volume of air is uselessly heated and discharged by the chimney. Non-bituminous fuel is more easily burned perfectly than