Fig.1 represents a skeleton frame dial, cast all in one piece; the eight central divisions are very thin, and curved, so as not to coincide or interfere with the hands while passing over them; the spaces are all filled up with transparent red glass, ground rough on the inside. This by day is sufficiently dark to relieve and render distinctly visible the gilt hour numbers; but at night, when the gas burners behind the dial plate are lighted up, the hours, minutes, and hands appear black, and the rest of the dial glows with a dusky red light. Fig. 2 is a horizontal section across the aperture a a in the church tower at the back of the dial b b; c the tube which carries the hour hand, having a balance weight and the wheel 48 on its inner end; through this passes the shaft d d, holding at one end the minute hand, and at the other end the pinion 14 and balance weight e; f f two gas burners; g g the tubes supplying the gas; the aperture a a, not being so large as the dial, is cham-ferred off at i i, to give a clear passage from the lights all over the dial; j j a curved reflector, made of sheets of tin; k k a bar crossing the aperture a a within, to support the motion wheels, and the additional twenty-four-hour wheel, 96; the long axis d d receives motion from the clock (as usual) by a bevel wheel; 14, 42, 12, and 48, Fig. 3, are the usual motion wheels and pinions; an additional pinion of 12 is put on the wheel 42, to turn the wheel 96; this has thirteen pins, one hour's motion apart; these pins raise up the weighted lever l, in Fig. 3, and let it drop; while this is up, (as shown by the dotted lines,) its opposite end m, by means of the connecting rod n, keeps the lever handle o of the gas cock p down, and thus nearly closes it, allowing the passage of only just enough gas to keep the burners alight; but at eight o'clock, when the weight / drops, it raises the handle o and quite opens the cock p, by which the dial is instantly illuminated.

Thus, Fig. 3 represents the lever l down, and the pins nearly beginning to raise it; by removing two pins, one at each end, the clock will open the gas-cock one hour sooner, and nearly close it one hour later. By successively removing the pins as the days shorten, and replacing them as the days lengthen, the clock is accommodated to all seasons. The whole space is kept clear between the lights and the dial, except only the axis e, Fig. 2; and the lights being placed on each side of this, and having a large reflector, no shadow is perceived from it.

Reference To The Engraving 541

Fig. 1.

Reference To The Engraving 542

Fig. 2.

Reference To The Engraving 543

Fig. 3.

Reference To The Engraving 544

With respect to the quantity of gas obtainable from a given weight of coal, it depends greatly upon the quality of the coal, and also upon the construction of the retorts, and the method of working them. Mr. Peckston, in his valuable treatise on gas lighting, whilst writing on this branch of the subject, observes that pit coal may be divided into three classes, according to the proportions of its component parts. Such coals as are chiefly composed of bitumen are to be considered as belonging to the first class. These coals burn with a bright yellowish blaze during the whole process of combustion; they do not cake, neither do they produce cinders, but are reduced to white ashes. At the head of this class is to be placed Cannel coal; and most of the varieties of Scotch coal, as well as some of those found in Durham and Northumberland, belong to it, likewise the coals from Lancashire and the north-western coasts of England. When ellipsoidal retorts are used, (which is the form which Mr. Peckston decidedly prefers,) and charged with 11/2 bushel, or about 126lbs of coal, the following quantities of gas may be obtained in the manufactory, or on the large scale.

From a ton of

Lancashire Cannel

11,600

cubic feet of gas.

Newcastle (Hartley's)

9,600

"

Staffordshire (best kind)

6,400

"

The coke obtained from coals of this class is in small quantity, and of very inferior quality. The second class of coals comprehends those varieties which cake in burning. These contain less bitumen and more charcoal than the first class. They produce less ashes, but afford hard grey cinders, which when burnt over again with fresh coals, produce a very strong heat. The gas obtained from these coals is not of so rich a quality as that from the first class, but the coke is extremely well adapted for domestic and culinary purposes. When ellipsoidal retorts are used, charged as before, with about a bushel and a half, from a ton of

Wallsend, may be obtained . .

10,300

cubic feet of gas.

Temple Main

8,100

"

Primrose Main

6,200

"

Pembry

4,200

"

The third class of coal consists of such as are chiefly composed of charcoal, chemically combined with different earths, and containing little or no bitumen. Amongst the varieties of this coal are the Kilkenny coal, the Welch coal, and the stone coal. None of the coals comprised in this class can be profitably used for making gas.

Mr. Peckston gives the following table, exhibiting the comparative quantity of gas obtainable from the following different species of coals comprehended in the first and second classes, the Scotch Cannel coal being considered the standard, and estimated at 1000.

Scotch Cannel

1000

Lancashire ditto ....

986

Yorkshire ditto ....

949

Bewicke and Craister's

Wallsend

875

Russell's ditto

861

Tanfield Moor

850

Heaton Main

822

Hartley's

810

Killingworth Main . . .

792

Pontops

762

Temple Main ....

690

Manor Wallsend . . .

650

Forest of Dean - Middle

Delf

612

Eden Main

562

Staffordshire coal, 1 st kind

546

Ditto ditto, 2d ditto

514

Ditto ditto, 3d ditto

492

Ditto ditto, 4th ditto

490

Pembry

354

With respect to the best form of retorts, and the mode of working them, so as to produce the largest quantity of gas, we give the following summary of three sets of experiments detailed in Mr. Peckston's work; the coals in each instance were of the same quality. 103 chaldron 12 bushels, distilled in circular retorts, charged with 2 bushels of coals, and each charge worked off in 6 hours, afforded 8300 cubic feet of gas per chaldron, and required 43 chaldron 14 bushels of coals for heating the retorts, = 42 per cent, on the quantity employed for making gas. By cylindrical retorts charged with 2 bushels at each charge, and which was worked off in 8 hours, 85 chaldron, 27 bushels of coals yielded 10,000 cubic feet of gas per chaldron, and required for carbonization or heating of the retorts 21 chaldrons 16 bushels of coals, or about 25 per cent, of the quantity carbonized. With ellipsoidal retorts, the two diameters of which were 20 inches and 10 inches respectively, charged with 11/2 bushel, and each charge worked off in hours, 61 chaldron 8 bushels of coals yielded 14,000 cubic feet of gas per chaldron, and required for carbonization 19 chaldrons 27 bushels of coals, or 32 per cent, of the quantity carbonized.

Mr. Peckston likewise states that five elliptical retorts are capable of carbonizing 45 bushels, or 33 cwt of coals, in 24 hours, but their average work may be taken at 1 chaldron, or 27 cwt. in that time.

Mr. Anderson, of Perth, made a great number of experiments, to determine the comparative quantity of light afforded by candles and coal gas; the size of the candles which he employed, was short sixes. The following are some of the results: -

A 3-jet burner consumed

per hour

2,074

cub. in.

= 6 candles.

An Argand of 5 holes

"

2,592

"

8 "

Ditto 10 „

"

3,798

"

12 "

Ditto 14 „

"

5,940

"

191/4 "

Ditto 18 „

"

6,840

"

21 "

The mean of these results is, that 324 cubic inches of coal gas yield light equal to that of one candle for an hour; but this is the coal gas of Perth, the specific gravity of which, Mr. Anderson says, is 650.