We continue our extracts from King's work on the Steam Engine, published by F. A. Brady, 24 Ann-st. On Coming into Pprt. After the engines are no longer needed, before hauling the fires, after a long run, it would be well to try the pistons and valves, in order to ascertain if they be leaky. To try the piston, open the water valve on one end of the cylinder and the steam valve on the opposite end ; if the piston leaks, the steam will escape through the water valve. To ascertain if the steam valves leak, open the water valves on both enus of the cylinder. To ascertain if the exhaust valves leak, open the stenm valves and any cock in the exhaust side of the steam chest or exhaust pipes. While under way it maybe discovered that there is a slight thump in the engine when passing one or the other or both centres, ana the indicator having been applied shows the usual lead, the inference is that some pnrt of the working engine is loose; it is important, therefore, to find out what it is on coming into port. To do this place the engine on the centre, and give the piston steam suddenly by raising and lowering the starting ba,' ; observe closely the cross-head, crank.pin, main-shaft,and othe!' main connections, to see where the jar is. Should it not be discovered after this, jam the cross-head fast, so as to pre\-ent the slightest motion, and then givc steam as before, in which event, if the thump be still felt, the piston will doubtless be found to have worked a little loose. If it be the intention to remain in port several days, before hauling the fires, sufficient steam should be raised, if the boilers be capable of bearing the preSSl1re, to blow all the water out of the boilers. After the boilers become cool, the hand-hole plntes, ovcr the furnaces particularly, shoulJ be taken off, to cxamine the crowns, where the greater amount of scale will be found deposit. ed, and from which we can judge if the boilers require scaling. Mere dampness iu boilers is found to be injurious, by occasioning a rapid oxidation, and in order to prevent this, one or two hand-hole plates should be taken off the bottom of the boilers, in order to let the water dmin out dry. It would be well aho to remove a man-hole plate from the top of the boilers to allow a circulation of ail'. Ii these things cannot be done it will be bette)' to keep the boilers filled with water, mther than a small quantity in the bottoms. In damp climates such as the Isthmns of Pnnnml\, light fires should be made in the ash-pits occasionally. Scaling Boilers. Notwithstanding the watcr in the boilers is not .it lowed to cxceed in dcnslly 1 ! to 2 per saline hydrometer, it will be found after a time that a quantity ot scale, compused principally of lime, has accumulated on the crown sheets, tubes or flues, and other parts of the boiler. If this be ulloweu to remain the metal will become overheated and burned ; it becomes nccessary, thcrcfore, to remove it, which can be alone done by mechanical menns. Sharp-faced “ scaling hammers “ can be used to knock the s('ale off these places that are within thc arm's reach, and long bars flattened at both ends, and sharpened, called “scaling bars,.”will knock it off the more remotc parts. In the Martin tubular boiler, which is acccssible in every part, it is only necessary to condense the steam in the boilers for a day or so after thc ship comes to unchar; this will soften the scalc so that a gang of lUen may be put into them as soon as the man-hole plntcs are removed, and scrape off all of it in a few hours. The scale, however, must never be allowcd to cxceed the thickness of writing paper. It has been proposed in some quarters to heat the tubes or flues by burning shavings, or some other such snbstances in them, and then to cool them off suddenlv by pumping cold water upon them, the sudden contra;. tion causing the scale to crack off. The plan, however, to our mind, uocs not ucserve much favOl', and never should he resorted to, if the scale can be reachcd in any other mnnner, for the production of leaks will mostly alwnys be the result! It is, hOlVeyer, hoped that engineers will soon be reo lieved from this duty, anu steamer owners benefited by the introduction of frcsh wnter condensers into all sea steamers. Preparatory to coming to AnchOl', 01' securing to the Wharf. Fifteen or twenty minutes before coming to anchor, or making fast to the wharf, the chicf engineer should be informed of the fact by the officer of the deck, or some other person informed on tho matter, so that the fires can be allowed to burn down, and the pressure of steam permitted to fall to such an extent that the necessity for blowing off is avoided. By this means the great nuisance of blowing off steam is not only obviated, but there is a considerable saving in fuel, the fires being permitted to burn down sufficiently low to supply only the amount of steam required while working the en gines by hand, rendering it mnch easier also on the firemen (whose duties on any occasion are arduous enough) by having a very light instead of a very heavy fire to haul. Incoming to anchor it is usually well to pump a little extra water into the boiler, so as to insllI'e a proper supply while operating the engines by hand. When it is desired to raise steam, the order from the captain should always be whnt time it is intended to get nnderway, leaYing to the discretion of the chief engineer to start the fires at such time as he m"y consider proper, in oruer to secure steam and every thing ready at the proper time. ?..—