exposed to the continual corroding action of the water. Owing to the high pressure at which locomotive boilers work as compared with stationary boilers, this springmg action would without doubt be more severely felt in boilers of that type; consequently the tendency to corrosion from this cause would be greater. It is also found that this detrimental action is increased when frame stays or brackets offering a special resistance to the expansion of the boiler are used. To obviate as far as possible the excessive corrosion at the rivet joints, a plan often pursued is to roll the iron plates with gradually thickened edges, which distributes the springing action over a considerable area. Welded joints seem also to exercise a tendency to prevent corrosion by removing the especial strains found in using lap-welded joints.

Should more than 25 horse-power be required, it is preferable to use a pair of boilers instead of one.

All Cornish boilers above 12 horse-power should be constructed with double flues, and fitted with Cross or Galloway tubes, and should in addition be thoroughly stayed. It is a trite but not unnecessary remark in these days of unfair trading and excessive competition that when human life is at stake only a first-rate quality of iron should be used in the construction of steam boilers, and where the action of the fire comes in direct contact with the plates, iron of the very highest possible quality only should be used. For forest use, or where machinery has to be moved from place to place, the ordinary portable engine and boiler on wheels is to be preferred. The different forms of three-cylinder engines, such as the Brotherhood, Willans', &c., although using a considerable amount of steam, are

sometimes found useful in driving single machines. Where the rate of speed is not too high they are often fixed directly on to the main spindle. In the recent (1878) International Exhibition in Paris we saw attached directly to the bottom saw-wheel spindle of a band sawing machine, exhibited by Mons. J. Fau, of Bordeaux, a new form of rotative engine, patented by P. Martin. It was capable of running at a very high rate of speed, but as to its advantages or the reverse we are not in a position to speak.

Great care should be exercised in setting the boiler, and the draught should in all cases be regulated by an automatic steam-damper, which, as it requires no attention and is regular in its action, effects a considerable saving over the old form of slide damper, the working of which is oftentimes neglected by the fireman. It may not here be out of place to remark on the false economy of employing so-called 'cheap labour in the management of engines and boilers, as it has been proved beyond doubt that an intelligent trained man, who has some knowledge of the properties of steam, who knows the economy of keeping a bright even fire and his boiler, safety valves, gauges, &c., clean and in good condition, will, in the course of twelve months, get extra duty out of his engine, and effect a saving in fuel and repairs very much in excess of the extra wages paid him. The explosions which almost daily occur, occasioning great loss of life and destruction of property, are generally attributed to either the culpable ignorance of the attendant or to the use of worn-out or badly constructed boilers. The subject of granting certificates to engine-drivers and placing steam boilers under Government inspection has

of late years been moved in the House of Commons on several occasions, and although, doubtless, a moderate Act would be for the general public good, the question seems to have been, at any rate for the present, quietly shelved.

The boiler and all steam pipes should be covered with felt or other non-conducting composition, to prevent radiation of heat or freezing. The composition known as Leroy's gives for this purpose satisfactory results, but we hear highly spoken of a later introduction, known as Toope's patent. This covering is composed of hair, felting, and paper, which is protected from charring by an interior lining of asbestos. It is said to be an admirable non-conductor, has absolute freedom from cracking, is light and easily fixed or removed, and is indestructible at any temperature at which steam is used. If it is found to fulfil all these conditions, it will, without doubt, be of great value to steam-users, as it overcomes several objections to most of the boiler coverings now in use, not the least of which is that it is entirely free from the crumbling action now so often found.

Before concluding our remarks under this heading we should wish to draw our readers' attention to the great practical value of the mineral abestos for packing steam piston and pump rods, stuffing boxes, &c., and when combined with felt it is an excellent covering for steam boilers. Although its existence has been known for many centuries, it is only during the last few years that its valuable properties have been utilised. Asbestos of the best quality is found in considerable quantities in the Italian Alps; it is fibrous in texture, and is capable of being woven or combined with other mate

rial. It also possesses the peculiar property of being unaffected by the action of fire, acids, friction, or moisture. It can also be used in the form of paste or millboard for steam and other joints. It is also very well adapted for packing steam fittings, such as cocks and water gauges, and we can, from our experience, speak in favour of its valuable qualities. Compressed wood pulp made up in the form of annular rings for glands, and sheets and washers for steam joints, has several features to recommend it, notably that the joints are easily broken and renewed, that the pulp readily retains the lubricating matter employed, and is anti-corrosive and will stand superheated steam. For glands the packing is usually made in segments of the exact size of the stuffing box.

CHAPTER XXX.

ARRANGEMENT OF SAW MILLS AND ECONOMICAL CONVERSION OF TIMBER.

A SAW MILL being for the purpose of converting crude material into articles of commerce and general utility, the great point to be aimed at is how to accomplish this with the greatest economy and despatch combined with quality of production. Saw mills being often situated in crowded cities, where space is of great value, and where any kind of building has to do duty, a set plan for laying out or designing a mill can hardly be laid down, but must vary according to circumstances. The following hints, however, may not be out of place :

Where space is obtainable, buildings should be arranged with large sliding doors at either end of the mill, so that timber may be passed in at one end in the rough, and, after being worked through the various machines, passed out at the other as manufactured goods. A tramway should run down the centre of the mill, and where much heavy timber is worked an overhead traveller is necessary. In arranging a mill advantage should always be taken of the site with reference to land or water carriage of the timber. If near a canal or river, the mill should be so arranged