enough. Usually, when first put in, a boiler and engine are large enough; but as business increases more machinery is added, until the power required is greater than can be furnished by the engine, more pressure has to be carried and the number of revolutions increased, consequently the evaporating power of the boiler is forced beyond its ability, the steam being drawn off so rapidly that a large portion of water is drawn with it so much that it would astonish any engineer if he had a testing apparatus attached to the steam pipe.

For the remedy of foul water there are numerous contrivances to prevent it from entering the boiler, which is a far better way than trying to extract the sediment after it is there-though there are many ingenious methods for doing that also. Faulty construction, or lack of capacity, the engineer cannot help, but he soon learns how to run the boiler to get the best possible results from it.

Every intelligent engineer has observed that his engine has an individuality not possessed by any other he ever ran, and nothing but personal acquaintance can get the best work out of it; so it is with the boiler.

The steam pipe may be carried through the flange six inches into the dome, which would prevent the water from entering the pipes by following the sides of the dome as it does.

For violent ebullition a plate hung over the hole where the steam enters the dome from the boiler is a good thing, and prevents a rush of water by breaking it when the throttle is opened suddenly.

Clean water, plenty of surface, plenty of steam room, large steam pipes, boilers large enough to generate steam without forcing the fires, are all that is required to prevent foaming. A surface blow-off is a grand thing, and helps a foaming boiler, and would be a good thing on every boiler, as you can then skim it as you would an open kettle.

STEAM GAUGES.

Steam-gauges indicate the pressure of steam above the atmosphere, the total pressure being measured from a perfect vacuum, which will add 14 7-10 lbs. on the average to the pressure shown on the steam-gauge.

BLOWING OFF UNDER PRESSURE.

A boiler can be seriously impaired by blowing it down under a high pressure, and with hot brick-work. The heat from the latter will granulate the iron and reduce its tensile strength. A boiler should not be blown right down under a higher pressure than twenty pounds and not less than four hours after the fire has been drawn,

When a boiler is exposed to cold air, especially

in the winter, it is advisable that the damper be closed and the doors thrown open, or vice-versa. If both are left open the strong draught of cold air will cool off the flues faster than the shell; which abuse if kept up would reduce the length of the life of the boiler.

POLISHING AND FINISHING METALS.

Take, for instance, a surface of steel as an example-the square stem of a drilling instrument will form a very good subject. After it is roughed out, and the work all done, it must be draw-filed, and this must be done with a superfine American file, and the lines must be kept quite straight, otherwise it will require so much emery-paper that the edges will lose the sharp angles which are the beauty of the work. Any ordinary workman can rub away with emerypaper, but in so doing he may spoil the appearance of a piece of good work, and that without knowing it. To avoid this, the smoother and better it is filed the less paper will it require. To get the beautiful finish we see on the best work, a piece of flour emery-paper, well worn, and a little oil upon it, will be found the best thing to use, and when this has been well worked, to get the high polish, a piece of wood flat upon the surface, with some fine crocus, will bring it up to this state; and if any deep scratches be there, you will at once observe them; to remove them, in all probability, it will have to be filed over

again. Now, to avoid all this loss of time, great care must be taken that the scratches are removed before any attempt is made to polish. Having finished the work so far, many prefer to see it left straight; others, again, like to see it in some way ornamented. Now, there are several ways of doing this. First, then, to cross the surface. This is done by folding a piece of emerypaper tightly round a file, but the process is not the merely pushing it across the work and making a mark, but it requires some practice to produce a good pattern, and the wrist must take a kind of circular action, and by doing this each line becomes, so to speak, connected, and makes a much better finish than a series of lines only. Another process of finishing steel is to curl all over the surface with a piece of oil-stone that will cut. This is a most difficult thing to obtain, as very few stones will cut steel to leave the bright marks necessary to give it the appearance desired. When a piece of this is once obtained it is really a prize, and if it wears away it may be inserted as far as possible into a wooden handle. To use the stone when it is once obtained is the next thing. This is done by holding it firmly in the hand and moving it about in all directions, like curling brass. There is no stated number or size of the curl, but this is quite a matter of taste, and must be left to the operator. Another way of finishing iron and steel is with

the scraper, which is used with both hands, and the work must be scraped in various directions, but with regularity. Large surfaces are sometimes done in this way. Lathe beds are at times done so, but we think this is somewhat out of character, as the fact of continually drawing the poppet head up and down the bed produces a series of lines which look most unsightly. Regarding all this, it is all a matter of taste, and the style of finish must be left to the operator.

WORKING STEEL FOR TOOLS.

In working steel for tools, great care should be taken to hammer all sides alike, for if one side is hammered more than another it will cause it to spring in hardening. Again, steel, when being hammered, should be heated as hot as it will stand, until finishing, and should then be hammered until almost black hot, for the reason that it sets the grain finer, and gives the tool a better edge. The reason for heating the steel so hot while hammering is simply because it makes the steel tougher when hardened, and softer when annealed, while, if it were worked at a low red heat, the continued percussive shocks of the hammer would so harden it as to make it almost impossible to anneal it, and at the same time render it brittle when hardened.

TO HARDEN AND TEMPER CAST STEEL.

For saws and springs in general the follow