M. Witz, says the Gas World, has been conducting a series of experiments on the Delamare-Deboutteville and Malindin gas engine, driven by Dowson gas, and in which the gas generator takes the place of the ordinary steam boiler. The engine was a one-cylinder motor in the establishment of Messrs. Matter & Co., Rouen. Its power was 100 horse indicated; the cylinder was 23 inches in diameter, the stroke 38 inches, and the normal speed 100 revolutions. The engine is of the Simplex type; the kindling is electric; the cycle of operations is fourfold, with powerful compression. The Dowson generator is 30 inches inside diameter and 76 inches in height from the bars to the top. Air is blown in by steam driven in under the hearth. There is a siphon, a coke scrubber 110 inches high, a sawdust purifier, and a gasholder of 750 cubic feet capacity, and a pipe to the engine 5.2 inches in diameter. The total area occupied by this apparatus is 140 square yards, of which two-thirds are built on. The anthracite employed was from Swansea, containing 5.4 per cent. of ash. The observations made with a string friction brake were continued for 68 hours, everything used being carefully weighed and measured.

One day the machine was worked for 15¼ hours on end; the other days it was worked with an interval of half an hour every 12 hours to clear the hearth, poke the fire and lubricate the machine; and it was clearly established that with a big enough generator it would be quite possible to work continuously for several days.

The following were the data for a day of 24 hours, with an interval of half an hour: 8:55 P.M. one day to 8:55 P.M. the next, interval 8:30 to 9 A.M. Anthracite used, 18.4 cwt.; coke used, 3.42 cwt.; water used for steam injection, 217.3 gallons; water used in scrubber, 4,106 gallons; water used in cooling the cylinder, 20,000 gallons; oil used in cylinder, 14.84 pounds; grease, 1.8 pounds; revolutions of machine, 142,157, or 100.8 per minute; effective work, 75.86 French horse power, or 77.4 British; gas used, 6,742 cubic feet per hour, at 772 mm. pressure and 70.7° F., or 83.7 cubic feet per effective horse power; efficiency, 69 per cent.

Now, with regard to the comparison between the large gas motors and steam engines of the same size, M. Witz goes on to remark that the gas engine is by no means, as was formerly thought on high authority, necessarily restricted to the domain of smaller work and sizes. Even in early times it was seen that the gas engine belonged to a type in which there were possibilities of improvement greater than those available in the steam engine, because the difference of temperature between the working substance in its hotter and its cooler condition was greater than in the steam engine; and consumptions of 5,250 cubic feet per horse power per hour soon descended step by step as far as 2,060, while the power went up, past 4, 8 and 12, to 25 or 50 horse power; and in the exhibition of 1889 there were gas engines seen in which the explosion chamber had a diameter of as much as 23 inches.

But the price of coal gas seemed to be too high for use in these large engines, in which sizes steam is comparatively cheap; and so poorer gas, which, though possessing only about 28 per cent. of the heating power, is still cheaper in proportion than coal gas, when it is made on the spot, was introduced to tide over the difficulty. Difficulties have been successively overcome, with the result which we have just seen, namely, 1.37 pounds of anthracite per effective horse power, or about half the carbon which a steam engine of the same power of excellent design, and well kept up, would consume. A 50 horse simplex at Marseilles, in Barataud's flour mill, is said to have run for the last 2 years on 1.12 pounds of English anthracite per effective horse power; and thus M. Witz says his predictions of 10 years ago, that the gas producer would some day replace the boiler, are being verified in such a way as to surprise even himself.

But the objection is stated, and it is a serious one: the weight of fuel is not the only thing to be considered. The steam engine uses coal, the producer requires English anthracite, which is dearer; the gas motor uses a great deal of water and a great deal of oil, which cost money; and gas motors are dear, while gas producers and their adjuncts cost a tidy bit of money, and wear out pretty fast. Is not steam, after all, more economical in the long run? Besides, producers are bulky and take up a great deal of space; the weight of fuel is only one element in a complicated problem.

In order to study the grounds of this objection, M. Witz has instituted a comparison between the actual cost of large steam engines and that of gas motors of similar size.

Take a good Galloway or multitubular boiler; for 75 horse power effective the heating surface must be at least 74 square feet. Using good Cardiff coal, with 4 per cent. of ash, and a heating power of 15,660 Fahr. units; the steam raised will be 8 to 9 pounds per pound of coal, so that 9,400 to 10,577 Fahr. units are utilized in raising steam, or 68 to 76 per cent., which is an excellent result. Take an engine of 16 inch cylinder diameter, 40 inch stroke, and 66 revolutions, etc.; it will use 22.4 pounds of steam per horse power effective, which represents 2.47 to 2.8 pounds of coal under the boiler. These 10 pounds of steam carry 11,752 Fahr. units of heat, and produce work equal to 75 horse, or 1,143 Fahr. units of heat; which corresponds to an efficiency of 9.7 per cent. In a gas motor, on the other hand, we find the materials employed, as per the above data, to contain 8,958 Fahr. units of heat, and to make gaseous fuel in which 6,343 units are available; a return of 70.6 per cent, in the producer. The motor receives these 6,343, and converts 1,143 of them into work; an efficiency of 18 per cent.

In order to be equivalent from the heat point of view, a steam engine ought to produce a horse power effective per 9.72 pounds of steam at 5 atmospheres; but no such steam engine exists.

M. Witz goes on with comparative estimates. For a Corliss engine and boiler, with chimney, etc., complete, and putting these up, he allows £1,280; for a Simplex gas motor and Dowson producer complete, including putting up, he allows £1,290, which he explains to be average actual prices; but these prices do not cover cost of transport, and M. Witz does not go into cost of masonry for buildings, apart from foundations, etc., for the apparatus and machinery.

As to water, the gas motor takes 215 cubic feet per horse power effective. A condensing steam engine uses five times as much.

The lubricating oil used at Rouen was a mixture of Russian oil at 430 fr. per ton, and Ferry and Heduit F.H. oil at 900 fr.; the average was 650 fr. per ton, or 2.8d. per pound. Wanner grease, at 6.4d. per pound, was used for the moving parts. A steam engine requires less oil for the cylinder, but the same quantity for the moving parts.

The attendance on the gas motor is too much for one man, not enough to occupy two; reckon it at 4s. 9½d. a day.

These elements enable us to calculate the daily cost of the gas motor, of 75 actual horse power, in comparison with a steam engine of the same size.

Steam Engine.

 s. d.

Upkeep, interest and sinking fund at 15 per

cent, on £1,292 = £193.8 = per day. 12 11

Cardiff coal, 2.643 pounds per actual horse

power per hour; 2.643 × 10 × 75 = in 10

hours 1,982 pounds coal at 22s. a ton. 19 5½

Oil, 3.36 pounds per day at 2.8d. per pound. 0 9½

Grease, 0.67 pound at 6.4d. 0 4½

Wages. 4 9½

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£1 18 4 

Gas Engine.

 s. d.

Upkeep, interest and sinking fund at 15 per

cent. on £1,292 is, per day. 12 11

Anthracite, 1.156 pound per actual horse

power per hour = for 750 horse-hours, at

25s. 6d. 9 10

Coke, 0.215 pound × 10 × 75 = 161¼ pounds

at 28s. 2 0

Oil, 0.0084 pound per actual horse power per

hour, or 0.0084 × 10 × 75 = 6.28 pounds at

2.8d. 1 5½

Grease, 0.754 pound per day at 6.4d. 0 5

Electric kindling, on cost. 0 3½

Wages. 4 9½

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£1 11 8 

The big gas engine making its own poor gas, and running 10 hours a day, has thus the best of it in the comparison with the steam engine of equal power.