grooved pulleys on which the rope actually rests. The skips are made entirely of wrought iron, much like a dredger bucket. They weigh about 290 lbs. and carry 8 cubic feet, the total weight transported being thus about 1,000 lbs. They are hung on gudgeons, and empty themselves by turning over as soon as a single fastening is loosened. There are special mechanical arrangements for connecting the hanging skip with a small frame above, carrying two wheels which travel on the fixed "road." The whole is connected with a running endless wire rope which communicates the motion. It is inch in diameter, is driven by a portable engine at the loading end, and is kept taut by passing round a counterweighted sheave of 5 feet 9 inches diameter, capable of travelling upon cast-iron guides. The speed of the running rope is in general about 4 feet per second. Small steel couplings are fixed on it at intervals of 130 feet, and to these the successive skips are attached-the mechanism both for attaching and disengaging being self-acting. At the discharging end there is an apparatus of iron rails for transferring the skips from one road to the other; by making this portable and providing it with supports it is further utilised for shifting the ends of the tramway and the point of loading so as to follow the progress of the excavation. With the speed of rope and distance between skips given above the quantity of earth conveyed is about 40 cubic yards per hour. The changing of the skips at the loading point (and similarly at the discharging point) is managed by a single workman. Each empty skip, as it comes upon the return road, detaches itself just before it reaches the workman, who receives and pushes it on to one of the lines of rail leading to the face of the excavation. He has already put in position a full skip which has just arrived by the other line of rails; and the same coupling which has conveyed the empty skip picks up the full skip in passing, attaches it to the rope and takes it away along the tramway. Thus the whole number of men employed on the tramway, as apart from the excavation, is only six at the most. The engine employed is of 8 HP., but 2 to 3 HP. is found to be all that is required for the work. The laying down of the tramway was completed, though in the depth of winter, in less than ten weeks; and Herr Bleichert, the inventor, states that he has tramways at work on this system which are 2,400 yards long, with gradients of 1 in 3, and conveying earth to the extent of 500 cubic yards per day.

W. R. B.

On Traction by Chain and Rope in the Von der Heydt Coal Mine at Saarbruck. By C. VON WEBERN.

(Oesterreichische Zeitschrift für Berg- und Hüttenwesen, vol. xxv., pp. 371–372.) This mine has in different workings four systems of underground traction, two by rope and two by chain, so that it is well adapted

for comparison of the two methods. One of the chain roads (in the "Burbach" adit) is 1,925 yards long, and is worked by an engine of 50 HP., connected by gearing to the driving drums. These were originally made with catches to grip the chain, but it was found that these wore out in six months, and also damaged the chain. The present drums are about 5 feet 6 inches in outside diameter, made of cast iron in two segments, and have a thick lagging of oak set at an angle, and grooved to receive the endless chain. This latter takes one turn and a half round the drum, and is carried over rollers to the end of the tramway, where it passes round a horizontal sheave of which the diameter is equal to the distance between the centres of the two lines. Throughout the length of the road the chain is supported only by the coal trams (which run at an interval of about 30 yards), except where there is an abrupt curve, in which case the chain is guided by two grooved pulleys, one vertical and one horizontal, which are fixed on a masonry pier at the angle. The chain is thus lifted from the trams just before coming to the curve, round which the trams themselves run by their own momentum, and are again taken up by the chain on coming into the straight. There is no means of attaching the trams, the weight of the chain being found sufficient to effect the traction. The speed is about 5 feet per second.

Should a link break, it is at once repaired by the insertion of a spare link made in two sections taken lengthwise. Each of these has a gap in it to enable the adjacent links to be slipped in; and when this has been done the sections are united by pins. This gets over one main objection to chain traction, viz., the delay occasioned by breakages. At this mine the chains (which weigh about 5 lbs. per lineal foot) last from six to twelve months.

The total cost of erecting this tramway (exclusive of the permanent-way materials) was £4,250, of which £2,840 were for the engine and machinery, £762 for chain, and the rest for smaller items.

The other chain road is only 580 yards long, and is used for bringing forward to the screening sheds the trams delivered by a rope tramway at the mouth of one of the adits (the Van der Heydt). As the trams arrive in trains of great length, the chain tramway has to be brought to the very mouth of the adit in order that the last wagons of the train may be attached without hand labour; and it thus overlaps the rope tramway. This is got over by leading the chain over rollers mounted on posts, and making the supports of these rollers movable, so that they can be lowered to enable the chain to take hold of the full trams, or raised on the other side to lift it off those which are returning empty.

The two rope tramways have lengths of 1,900 and 4,124 yards respectively. A table is given showing a detailed comparison of the cost of their working with that of the two chain tramways. The totals (reduced to pfennigs per zoll centner per lineal mètre) are 2.549 for the shorter rope tramway, 3.047 for the longer, 3.811 for the shorter train tramway, and 1·951 for the longer.

The high figure for the first of the chain tramways is of course due to its length being so much below any of the others; and the results are considered as showing a very great economy in the system of chain, as compared with rope, traction.

W. R. B.

Compressed-air Blast for Steam Boilers.

By L. E. Bertin.

(Bulletin de la Société d'Encouragement, 3rd series, vol. iv., pp. 529–544.)

M. Bertin estimated, from the results of experiments, that the quantity of steam consumed for compressing air to act as a blast in the chimney of steam boilers amounted to only one-tenth of the quantity required when discharged direct into the chimney. The air-compressor employed by him was positive, consisting of two air cylinders, 24.4 inches in diameter, with pistons, and a direct-action 9-inch steam cylinder, with a common stroke of 152 inches. The normal speed was 65 turns per minute. The compressed-air blast was tried on one of the two boilers of the "Résolue," having the following dimensions:

The compartment containing engines and boiler was completely closed to the atmosphere, except by one passage having a sectional area of 9.80 square feet, through which the whole of the air for supplying the boiler was passed. As the experiment was confined to one of the two boilers of the "Résolue," the chimney was divided vertically into two parts, and the half which was used was subdivided into two, to each of which was devoted one blast-nozzle from which compressed air was discharged upwards. A variety of experiments were made on the power consumed and the velocity and supply of air, by the action of the compressed-air blast. It was found that with nozzles having respectively the sectional areas 4.6 and 11.6 square inches (30 and 75 square centimètres), equal duties in velocity and volume of blast were performed for equal expenditures of power. In a series of trials, in which the fires were lighted and the boiler was actively at work, nozzles of six different sections, from 1.55 to 11.6 square inches (10 to 75 centimètres) were employed. The following deductions were made

from the results of the experiments when the engine was working

to 18 HP.:

10 20 30 40 or 1.55 3.08 4.6

50

6.2

7.7

75 sq. centimètres. 11.6 square inches. 29.5 feet.

3.6 feet

Velocity of air entering) 26.6 27.2 27.9 28.5 29.5
stoke-hole, per second
Pressure of compressed)
air, in feet of water

Effective mean pressure

10.7 7.2 5.6 4.9 4.3

of steam in cylinder of 4.77 3.71 3.11 2.72 2.48 2.25 atmospheres.

blowing engine

Turns per minute

The velocities above noted are the total velocities attained, and they comprise the element of velocity, 19.7 feet per second, due to the natural draught.

The object of the next series of trials, which were made altogether with the nozzles of 4.6 square inches, was to measure the consumption of fuel and the production of power.

From this table, it appears that the power developed by the engine was more than doubled by the application of the compressedair blast, the power required for which did not exceed 5 per cent. of the power of the engine.

The rates of combustion and of evaporation have also been increased in a different manner, by completely inclosing the stokehole, and blowing air into it by a powerful fan, so as to maintain a pressure or plenum of from 4 to 5 inches of water.

D. K. C.

Shaw's Spiral Exhaust-Nozzle.

(Journal of the Franklin Institute, 3rd series, vol. lxxiii., p. 366.)

The spiral exhaust-nozzle, invented by Mr. Thomas Shaw, is designed to quell the noise of steam blowing off at the safetyvalves of locomotives and steam-vessels. A cylindrical coil of

wire is fixed to the end of the escape-pipe, above the valve, of such a length and diameter that, when it is compressed so that the coils come nearly into contact, the aggregate area of the interspaces is much greater than the sectional area of the escape-pipe. The helix is screwed down, adjusted to the required degree of compression, between two discs; and, as a self-acting means of providing some relief, should the interior pressure become excessive, a short helical spring is interposed between the holding-down nuts and the upper plate, to admit of a slight increase of the interspaces. The coil absorbs the vibrations of the escaping steam, which is subdivided and passed through the interspaces. The turns of the coil cannot vibrate to any considerable extent without touching each other, and neutralising the vibrations so that these are not transmitted to the air. The exhaust-nozzle has been favourably judged by a committee of the Franklin Institute, who "find that it accomplishes the object most effectively."

D. K. C.

On Travelling Cranes with Self-adjusting Balance Weights. BY PROF. K. KELLER.

(Wochenschrift des Oest. Ingenieur- und Architekten-Vereines, vol. ii., pp. 250–255.)

In this Paper the Author investigates several designs which have appeared at different times, for automatically adjusting the position of the balance weight of portable cranes. The arrangements discussed are those of Jambille, Michaud and Jay,2 Schnabel and Henning, Grosse, and Appleby.5 In some of these cranes the self-acting balance weight is only a secondary consideration, the main object being to weigh the load.

3

4

Jambille uses a balance box running on a tail carried out behind the crane in the usual manner, but curved upwards instead of being horizontal; the end of the hoisting chain, usually hooked to the jib-head, is taken over a pulley down to the end of the tail, and round another pulley to the balance box. Suppose the load be too heavy for a given position of the weight, the result will be that the hoisting chain, instead of lifting the weight, will haul the balance weight up the constantly increasing incline till a point is reached where the resistance of the curve is greater than that of the load, when lifting commences.

Professor Keller, following the method first used by Professor Weisz, investigates the equation to the path of the balance weight,

1 66

Engineering," vol. iii., p. 325.

3 English Patent, 1875, No. 505.

5 Patent, 1874, No. 1,285.

• Zeitschrift des Architekten- und Ingenieur - Vereins zu Hannover, 1873, vol. xix., p. 61.