In the production of steam the minerals found in impure or "hard" water which give most trouble are sulphate of lime, carbonate of lime, magnesia, oxide of iron, alumina, and silica. Dr. Joseph Rogers, an authority on the subject of incrustation, says the evil effects of scale are due to the fact that it is relatively a non-conductor of heat. Its conducting power compared with that of iron is as 1 to 37.5. The estimated loss of heat caused by lime scale is from 15 to 20 per cent. for a scale of inch thickness, which increases rapidly with greater thicknesses. When it is of an inch thick, 60 per cent. more is required; at an inch, 150 per cent., and so on. To raise steam to a working pressure of 90 lbs., the water must be heated to 320° Fah. If a 1-inch scale intervenes, the boiler must be heated to 700° almost a low, red heat. The higher the temperature at which iron is kept the more rapidly it oxidises, and at any temperature above 600° it soon becomes granular and brittle from carbonisation, and therefore liable to fracture, and doubtless many boiler explosions could be traced to this cause. The most troublesome of the minerals found in impure water is sulphate of lime, which is caused by the combination of oxide of calcium with sulphuric acid; carbonate of lime causes also much. trouble, this is composed of carbonic acid, resulting from the decomposition of vegetable or animal matter with lime or oxide of calcium. The combination of these two minerals with vegetable matter and mud forms a very hard dark scale. Oxide of iron forms a reddish scale, and is very injurious to boilers, as it is generally held to be one of the agents by which corrosion is set up; another and more dangerous one is sulphuric acid, found in mining districts, and which often causes rapid corrosion. This can be separated by heat on account of its specific gravity, which is 1.844; to do this the water requires to be heated to a temperature of at least 260° Fah.

The best form of feed-water heater with which we are acquainted is one (Strong's patent) in which the water is heated to the precipitating point, and a chemical separation takes place. In accomplishing this, exhaust steam is used up to 208° to 212° Fah., after which the temperature is raised to the precipitating point by means of a live steam coil. After the precipitation the water is filtered through wood charcoal or other suitable material, by which a mechanical separation of the impurities is effected; the purified water then passes out of the heater into the steam space of the boiler. The heater may be readily cleaned by a jet of live steam from the boiler.

In some countries water of extreme softness and purity may be found that renders a feed-water heater not absolutely necessary, but these cases are exceptional, and steam users-especially those employing tubular boilers-will, we think, find a good feed-water heater effect a considerable economy in fuel by preventing incrustation, and by utilising the waste steam and a small amount of live steam perfectly pure water may be passed into the boiler.

SETTING ENGINES AND BOILERS AND THE PRODUCTION OF STEAM.

In fixing the engine care must be taken that it rests at a dead level, both laterally and transversely. This can be ascertained by means of a spirit level and winding lath, which can be tried on the motion bars. The bed-plate of the engine should be securely fixed on a rigid stone or brick foundation. If the latter, three or more courses of hard bricks on a bed of concrete should be used. The foundation bolts should pass entirely through the brickwork, and be fitted with plates at least 6 inches square. They can, if wished, be cemented in their places. To lessen the vibration of the engine when in work, it will be found a good plan to fix it on a sheet of lead, or, failing

that, a piece of hard wood placed between the foundation plates and the masonry will render the bolts less liable to fracture or work loose from any sudden strain that may be put upon them.

The proper setting of the boiler is a matter of far greater importance than the setting of the engine, as much of the safety and economy in working depends on this being properly done. The boiler or boilers should always be

Fig. 1.-IMPROVED METHOD OF SETTING BOILERS.

arranged so that both internal and external examinations can readily be made. The masonry in which the boiler is set-we are now speaking of the Cornish or Lancashire type-must be good and sound, and should in all cases be lined with a course of fire-bricks or fire-clay. It should also be arranged with a return flue, or flues, so that the heat should pass completely round the boiler before it passes into the chimney stack, and be thus utilised to its fullest extent.

We give herewith (Fig. 1) an illustration of an improved method of setting Cornish or Lancashire boilers. As will be seen from the sketch, an almost complete external examination of the boiler may be made. Corrosion often takes place down the centre of the boiler, which is generally made to rest on a brick support or mid-feather. In the plan before us the bottom of the boiler is left entirely clear for examination, and corrosion at the seams can be easily detected.

With the object of retaining as much heat as possible, the external flues are often either omitted altogether, or made so narrow that it is impossible to make an external examination of the boiler without removing the brickwork. This is a great mistake, as often external corrosion may be taking place to a serious extent, and the boiler attendant be entirely ignorant of the fact. Should a mid-feather be used it should not be of greater width than is necessary to support the boiler, and small openings in the brickwork should be made through which the boiler seams may be examined.

The boiler should be set as nearly level as possible; if not, errors may arise as to the condition of the water supply, one end of the boiler containing more water than the other. To secure safety from fire, the boiler should be fired from outside the main building, and for convenience sake may be fixed a little below the ground level.

The top of the boiler should be covered with a good non-conducting composition to prevent radiation of heat. We have tried, with very satisfactory results, a thick covering composed of hair felting, and paper with an interior lining of asbestos to prevent charring. We have also heard very well spoken of the compositions known as slag wool and fossil meal, but cannot from our own experience give an opinion on them. In lieu of anything better, a mixture of cow-dung, hair, and sand will be found

effective. Whatever is used it should, if possible, be put on in sections, which could be removed periodically for inspection of the boiler. These sections could be made in light wooden frames, shaped to the form of the boiler.

In all cases the draught to the boiler should be regulated by a damper, and this, wherever possible, should be arranged to work by steam automatically, as it requires no attention and is regular in its action, and effects a considerable saving over the old form of slide damper worked by hand, as its regular working is often neglected by the boiler attendant. The steam damper can be arranged to act at any desired pressure of steam, and as the fire is automatically damped when that pressure is reached, a very considerable saving in fuel is effected.

An important factor in the economical working of boilers is the correct arrangement of the chimney stack, so that from a steady and not excessive flow of air an equal and steady combustion may be kept up in the boiler fire-grate. This is a point that is, we are afraid, somewhat neglected, the result being in many cases that fuel is burnt to waste, from the excessive area of chimney, and consequently excessive draught, or from insufficient area the draught is insufficient, and the fire consequently dull and sluggish. All bends leading to the chimney stack or funnel should be avoided as far as possible; if imperative they should be made as obtuse as possible. The chimney should be higher than adjacent buildings, as the draught is damaged by the currents or eddies of air caused by them. A general rule, which must, however, be modified according to circumstances, for height of chimney stack, &c., is to make the flues and area of the chimney top equal to from 2 to 3 square feet for each boiler, having about 30 square feet of fire-grate, the 2 foot area being given for chimneys over 150 feet high, where several boilers are working together. Another common rule is to make the flues and area of the