was reversed. Now if this quantity of steam, or a half cylinder full, were compressed into the clearance space its pressure would be increased in proportion to the decrease in volume. With a D valve, however, the valve can lift and so allow this excess pressure to flow into the steam chest, and from the steam chest up through the steam pipes and dry pipe, and through the open throttle into the boiler. Consequently, the increase in pressure in the cylinder, due to reversing the engine, on an engine equipped with a slide valve, is but little above the boiler pressure providing the throttle is open. If the throttle is closed, however, the instant that the engine is reversed, the increase in pressure would be considerable, as has been noticed by a steam chest being blown off, etc.

On a piston valve engine, on account of the valve fitting snug in its bushing, and, consequently as it can not be raised to relieve the pressure, the pressure in the cylinder would be proportionate to the amount that the steam in the cylinder has been compressed in volume, less the difference due to what leakage would pass by the valve and piston head. This, unless steps were taken to prevent it, would usually result in the cylinder head being blown out, and for the above reason cylinder relief valves are used in connection with piston valve engines.

1869. Carbon in Bituminous Coal.-"What per cent. of carbon is in average bituminous coal?"-H. J. S.

Answer. The composition of ordinary bituminous coal runs about 50 per cent. fixed carbon, 40 per cent. volatile matter and moisture, 10 per cent. ash.

1870. Feed Water Heaters.-"Please give me full description, with drawings, if possible, of the feed water heater for heating water to boiler temperatures after same leaves injector, that is in successful use now, or any that are being experimented with to your knowledge."S. L.

Answer. While there have been quite a number of feed water heaters used on locomotives at various times, yet so far as the writer knows there are but two general types in successful use at the present time. Neither of these, however, heat the water to boiler temperature, as were this the case you can readily see no boiler would be necessary, the temperature of the water in the boiler being the same as the temperature of the steam.

These feed water heaters, however, utilize heat that would otherwise be wasted, such as the waste heat from the smokebox gases and the waste heat in the steam from the air pump exhaust, and while the water is not heated to the same temperature as the water in the boiler, its heat, however, is materially increased, and in this way results in some economy in fuel.

One very successful type of feed water heater is that known as the Gaines heater, Fig. 1, and used on the Central of Georgia Railway. This consists of two drums about 6 feet long and 15 inches inside diameter, and contain each 19 tubes 1 inches in diameter through which the exhaust steam from the air pump to the feed water pump passes. These drums are located under the running board, one on the right and one on the left side. Their operation can be briefly explained as follows: The feed water is taken from the tank by a duplex steam pump located between the frames behind the cylinder saddle and about on a level with the bottom of the tank. The water is delivered into the heater drum under the left running board, where it is heated by the exhaust from the steam pump and the left air pump. From the left hand drum the water goes under pressure into the right hand drum. From this heater drum the water is forced through the smokebox heater, which consists essentially of a set of Baldwin superheater coils, as shown in detail in Fig. 2, and from this through an ordinary boiler check into the boiler, the check being located in the usual place on the left side of the boiler. The condensed water from the exhaust steam is carried back into the tank through suitable connections where it heats the tank water from normal up to about 170 degrees, according to the temperature of the atmosphere and the service in which the engine is The use of these feed water engaged. heaters is said to result in a fuel economy equal to about 15 per cent. When the feed water heaters are not in use, water is supplied to the boiler through an injector in the ordinary manner. This precaution is also taken with a view to safeguarding any possible failure of the feed water pump.

Another type of feed water heater that is successfully used on the Santa Fe Railway, especially in connection with their Mallet locomotives, is that known as the Buck-Jacobs feed water heater. This

heater used on the Egyptian State Railways, called the Trevithick System, which is practically a combination of the Gaines and the Buck-Jacobs. With this system the feed water is drawn from the tender and forced into the boiler by means of a horizontal duplex pump located on the right side just ahead of the cab. This pump takes steam at boiler pressure and delivers its exhaust into the first section of the feed water heater, which is located on the suction side of the pump. This first heater is vertical and contains 19-inch tubes, which are connected to headers at each end, the upper header being connected from the exhaust pipe to the pump, and the lower header having an opening to the atmosphere. The feed water circulates around the outside of the tubes. On leaving the pump the water traverses in succession two other headers, one in either side of the smokebox. The one on the right is divided into two compartments by a partition, so that the water travels twice the length of the header in passing through it. It then goes to the left header, in which there is no dividing partition. These two headers are heated by part of the exhaust steam from the cylinders. From this the water passes to the larger header in the front

end, which consists of an annular chamber, containing 265 tubes 1 inch in diamcter and 18 inches long, arranged in three concentric rings, and heated by the exhaust gases passing through the tubes. The total section of the heater tubes, which is a little larger than the section of the smokestack, is entirely utilized, and their position in reference to the fire tubes assures a perfect separation of the escaped gases to the interior of them all. From this heater the water passes to the boiler through the usual check valves. An economy of from 22 to 27 per cent. in fuel is claimed for this type of feed water heater.

1871. Mallet Engine.-"What is a Mallet articulated compound engine?"-F. J. O. Answer.-The Mallet engine is SO named from its inventor. It consists of two separate and distinct engines under one boiler, and can be either simple or compound. The term "articulated" means jointed, and is derived from the fact that the forward engine is not rigidly attached to the boiler, thereby allowing the boiler to swing laterally over the engine or the forward engine to curve independently of the rear engine; there

fore, a Mallet articulated compound is a locomotive having two separate and distinct engines under one boiler; the rear engine rigidly attached, the forward engine flexibly attached, and the forward engine receiving power from the exhaust steam delivered to it by the rear engine.

1872. Control of Simple and Compound Features.-"How are the simple and compound features controlled in Mallet engine?"F. J. O.

Answer.-In the Baldwin type, by means of an emergency valve in the cab, which, when opened, allows high pressure steam to flow direct from the boiler into the receiver and from the receiver into the low-pressure cylinders. In the American type, by means of an intercepting valve and an emergency valve. When the emergency valve is opened it throws the intercepting valve in such a position as to allow high pressure steam to flow from the high-pressure steam chests direct into the receiver pipe, and from thence to the low-pressure cylinders.

1873. Disabled High-Pressure Engine."Should the high-pressure engine become disabled, how would you get the locomotive in?"-F. J. O.

Answer.-By opening the emergency valve in the cab, so as to allow high pressure steam to flow to the low-pressure engine.

1874. Disabled Low-Pressure Engine."Should the low-pressure engine become disabled, how would you get the locomotive in?"-F. J. O.

Answer. With the Baldwin type it would be necessary, if the valves were disconnected, to place them in such a position as to allow of a free exhaust from the high-pressure engine to the stack. With the American type simply open the separate exhaust valve. In both instances the locomotive could be brought in with the high-pressure engine only.

1875. Emergency Valve.-"Under what conditions should the emergency or starting valve be used?"-F. J. O.

Answer.-Only when starting, and to prevent stalling on a heavy grade.

1876. Intercepting Valve.-"What are the duties of the intercepting valve?"-F. J. O.

Answer. To supply steam to the lowpressure cylinders when starting, and to

cut off the supply when the reservoir pressure has reached the desired amount.

1877. Drifting Mallet Engines. "Why should a Mallet compound engine not be allowed to drift down grade?"-F. J. O. Answer. These engines can be drifted down grade providing the speed is not excessive. When the speed becomes excessive, however, owing to the difference in area in the high and low-pressure cylinders, the engine begins to pound, and the low-pressure cylinders to heat, and for this reason it is always advisable to work a little steam down grade; in fact, unless the grade is steep, it is usually necessary, as this type of engine does not drift freely. For a better understanding and a more complete answer to the above questions, we would suggest that you read the article on "Mallet Articulated Compound Locomotives," page 589, May, 1911, issue of the Magazine.

1878. Superheated Engines.-"What engines on this division are equipped with superheaters, and how do they differ from saturated steam engines?"-F. J. O.

Answer. It will be necessary for you to answer the first part of this question yourself, as we can not advise from this distance what engines are equipped with superheaters.

In reply to the latter part of your question, however, would say that a superheated engine differs from one using saturated steam in that the steam, after leaving the throttle valve, is superheated before it reaches the cylinders, that is, more heat is added to the steam.

1879. Superheater Damper.-"What is the object of the adjustable damper in the front end of this type of engine, and how is it operated?"-F. J. 0.

Answer. The object of the damper is to prevent the flow of hot gases through the smoke tubes containing the superheater elements when the throttle is closed, that is, when there is no steam in the superheater, as if the damper were allowed to remain open the superheater elements might become overheated if the throttle was closed and there was no steam in the elements. The damper is operated by means of a small steam cylinder, attached to the side of the smoke arch, containing a piston, which in turn is connected to a crank rigidly fastened to the damper rod. When the main throttle is opened, steam flows into the bottom end of this cylinder, forcing the

piston out, and this in turn opens the damper. When the throttle is closed, the steam in this small cylinder gradually condenses, so that the counter-weight attached to the other end of the crank, to which the small piston is connected, will fall, and close the damper again.

1880. Lubrication of Superheated Engines."Why is it more important that lubrication be constant with this type of engine?"-F. J. O.

Answer. Because the temperatures of the steam and, consequently, the valves and pistons, are higher, so that if lubrication were not constant it would result in cutting the valves or cylinders more readily than where saturated steam is used.

1881. Engine Not Steaming.-"If engine does not steam freely, where would you look for the trouble?"-F. J. O.

Answer.-See if the damper was open. This can be observed by the position of the counter-weight on the end of the damper shaft.

1882. Walschaert Valve Gear.-"Explain this type of valve gear."-F. J. O.

Answer. The Walschaert valve gear is what is termed the radial type, being all located outside of the frames. The movement of the valve is controlled by one crank arm attached to each main pin, this crank arm answering the purpose of both a forward and backing eccentric. The crank arm in turn is connected by means of a rod, termed an eccentric rod, to the bottom of the link, the link being hung on a trunnion and oscillating forward and back but not raising and lowering same as on a Stephenson gear. The lap is overcome and lead given the valve by means of a combination lever, sometimes called "lap and lead lever," its lower end attached to the crosshead by means of a short link, termed a "union" link, the upper end connected to the valve stem and to the radius rod, the radius rod being the rod running back to and connecting with the link block.

1883. Difference Between Stephenson and Walschaert Gear.-"How does this gear differ from the Stephenson link motion?"—F. J. O.

Answer. As stated above, with the Walschaert gear but two crank arms are employed in place of four eccentrics, as obtains with the Stephenson gear. With