same firms. As the poppet-valve depends on gravity to seat it, and as it must seat gradually, it is not used on quick-working engines.

A

Sea-Valves. Fig. 40 shows a section of the injection and outboard delivery-valves of the gunboat Nyack. There is not such great precaution taken in fitting the outboard delivery-valves as in the injections, as they are near the water-line, and are more accessible. As the water flows from the delivery, no strainer is required, thus leaving the hole open, which enables the engineer to plug it up when repairs are necessary. For an injection-valve the hole is carefully bored through the wood, and then counter-bored, conically, at the outer end. A lining of sheet-copper is then put in, having its seam brazed; the ends of this copper lining are then flanged over and secured to the surface of the ship, both inside and outside. heavy brass pipe, fitting this hole, is then pushed in, and a washer and nut on the inboard end pull it tightly in place. The pipe is then secured tightly, at its outer flange, to the ship by copper screws, after which the strainer is secured by screws. A flange is screwed to the inboard end of the pipe, and the valve bolted to this flange. The outboard delivery has the same lining through the wood, but the chamber is bolted to the wood of the ship, on the inside, by brass wood-screws. On large ships there is a ring of brass on the outside, and the valve-chamber is held by through-bolts. The "donkey pumps and the main bilge-pumps discharge, through a check-valve, into the outboard delivery, above the valve. It is now the navy practice to use rubber faces on the injection and delivery-valves, and to make the delivery-valve a check.

Where sea-valves pass through the vessel above the permanent filling-pieces, there are special filling-pieces supplied, that the piping may pass through solid wood.

STEERING APPARATUS.

THE use of steam for steering ships is of comparatively recent origin, but it has proved satisfactory, and there is indication of its coming into general use. An engine for this purpose must be of such simple construction that skilled labor is not essential for its successful operation; it must be certain in its action, it must be noiseless, and automatic to a certain extent; that is, it must push

the helm over a number of degrees depending on the volition of the man at the wheel, and must stop automatically when that angle is accomplished. It must be so arranged that, in the event of accident to the steam-engine, it can be detached and the hand gear thrown into use in a moment. Fig. 41 is a longitudinal view of

a steam steering and hand-power machine, combined; the right hand showing an elevation and the left hand a section. The steam steering-wheel h communicates motion to the steam reversing valve V, through the intervention of the shafts, gear wheels G and g, the nut n on the screw t, and through the floating lever L. When the

valve V is opened the engine E revolves, and through the friction (noiseless) gear-wheels revolves the drum D, on which the tiller ropes are coiled; but when the drum D revolves, its prolonged axis, S, on which there is a screw and a nut, N, also revolves and moves the floating lever L so as to stop the engine E, and it is so proportioned that one revolution of the wheel h will cause one revolution of the hand-wheel H, at which moment, the valve V being closed, the machine stops itself.

By withdrawing the key K, the friction-wheel F becomes loose upon the drum, and steering may be done by hand, entirely independent of the power gearing.

DISTILLED WATER.

SINCE the introduction of distilling apparatus on board the ships of the navy, diarrhoea has diminished more than fifty per cent. This arises from the uniform quality of the water, for men are frequently attacked by a temporary diarrhoea from simply a change of water. Ships taking water from various ports, even though great care be exercised, are almost certain to get bad water once in a while. Gibraltar has a much frequented harbor, and ships stopping there almost invariably take in water. The water is drawn from a well on the neutral ground. Before the well was sunk there was always water found in digging new graves in the adjacent cemetery, but since that event the graveyard is dry. It is not necessary to add that the well has drained the cemetery. Hard rains sometimes cause a rise of water in the sewers, in our large cities, and the head of water being greater than that in the adjacent springs and wells, there is a leakage of sewage through the soil into the wells, and the water is contaminated. This happened in a suburb of Philadelphia, only a few months since, which resulted in an epidemic of typhoid fever. The head of water in the sewer was greater than that in the spring for only a few hours, and the sewage had to percolate through about ten (10) feet of soil, besides the brick lining of the sewer, before it reached the spring. This spring had supplied the neighborhood with water for many years, and no suspicion rested on it until the eminent chemist Dr. Haines made analyses. Any apparatus which will condense the steam from the boiler without mixing anything else with it will make fresh water, but that water must

lie in tanks, exposed to the air, for some days before it is fit to drink. It contains organic matter which the air must have time to oxidize, and it is flat and insipid from the want of aëration.

The cost of distilled water at sea depends on the cost of the coal used, and on the efficiency of the boiler, and is entirely independent of the kind of distiller used.

46

The average price paid for coal for the navy, the world over, from 1869 to 1877, was $10.32 per ton, or (2238)=10 cents per pound.

The evaporative power of marine boilers is from 7 to 12 pounds of water per pound of coal, and the distilling apparatus is proportioned to condense all the vapor its pipe will bring.

A gallon of distilled water weighs 8 pounds, and assuming, for example, that a boiler evaporates 7 pounds of water per pound of coal, a gallon of water will cost (837) 1 pounds of coal, or (144) cents. Adding to this the loss incurred in blowing the boiler, which will not exceed 20 per cent., we have a cost of 0.656, a little over of a cent per gallon.

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A ton of distilled water will occupy 35.84 cubic feet, and a ton of coal will distil (7—(} × 7)=) 5.6 tons of water. A ton of coal occupies about 42 cubic feet, so that by carrying coal instead of water we save space in the ship for other things in the ratio of 5.6 to 1; or, instead of carrying 195.1 cubic feet of water, will carry 42 cubic feet of coal, leaving 153.1 feet for cargo.

Freshly distilled water has a flat, insipid, oleaginous taste, but becomes sweet and potable in from ten to fifteen days' exposure to the air. Its potability may be hastened by artificial aëration, and his may be done by a fountain,* by blowing air into the tanks,* or

the patented aërator, which forces the air into the steam before condensation. The first and second methods require to be oft repeated, and much time is necessary before the aëration is sufficient.

The organic matter brought into the still by the steam is oxidized by the great quantity of hot air present, as induced by the patented aërator, and is put in a condition to be removed by a proper filter. By placing the aërator some distance from the still, and by the addition of a small quantity of oxygen gas to the air used, the water has been made so good that it was difficult to distinguish it from hy.

* Journal of the Franklin Institute, vol. lxiii., page 63.