PART V.

Difference in the quantity of Gas evolved during different periods of the distillatory process, and economical considerations resulting therefrom in the manufacture of Coal Gas.

In conducting the decomposition of coal, the evolution of the gas is far from being, with regard to quantity, uniform during different periods of the distillatory process. The formation of the gas is more rapid in the beginning of the process, and gradually slackens as the operation proceeds. The gas also differs in its chemical constitution, at different periods of the process; although in the case of large supplies, this difference is of little consequence after the gas is purified in the usual manner. The former consideration, however, has given rise to various modes of operating, of which it will be proper to take some notice.

It must be obvious, that in proportion as the mass of coal in the retort becomes carbonized or converted into coke, the exterior surface becomes a gradually increasing obstacle to the action of the heat upon the interior or central part of the coal remaining to be decomposed. The heat required on that account must be more intense, and kept up to no purpose, and the extrication of gas becomes slower and slower, as the operation proceeds.

The loss occasioned by this rapid diminution of the means employed, is serious in every point of view, in regard as well to the quantity of fuel used and time wasted, but it is unavoidable in the operation of decomposing coal in masses or layers from 5 to 10 inches in thickness, and must be a great drawback on the value of the gas-light discovery.

The loss of fuel, it is obvious, must be just in proportion to the quantity of carbonised matter, or coke, which is kept hot to no purpose, awaiting the decomposition of that portion of coal, which it is the very means of protecting from becoming decomposed.

A striking exemplification of this statement will be seen in the following table, exhibiting the result of the progressive produce of coal gas, obtainable, in a given time, by means of cylindrical and parallelopipedal retorts.

Experiment with one cylindrical Retort, containing two bushels of coal.

Hours of the distillatory process	Quantity of Gas produced.
First hour	115	cubic feet
Second ditto	81	ditto
Third ditto	78	ditto
Fourth ditto	70	ditto
Fifth ditto	66	ditto
Sixth ditto	55	ditto
Seventh ditto	49	ditto
Eighth ditto	42	ditto
	555	cubic feet.

The quantity of gas is at the rate of ten thousand cubic feet to the chaldron (27 cwt.) of coal.

Experiment [14] with eighteen cylindrical Retorts, containing one chaldron of coal.

Hours of the distillatory process	Quantity of gas produced.
First hour	2000	cubic feet
Second hour	1488
Third hour	1400
Fourth hour	1301
Fifth hour	1208
Sixth hour	1000
Seventh hour	897
Eighth hour	691
	9985

This experiment was made with retorts set on the flue plan.

The coal employed was (Bewick and Craister’s Wall’s End), Newcastle coal.

[14] Communicated by Mr. T. S. Peckston, of the Westminster Gas Works.

Experiment with thirty-six parallelopipedal retorts, each containing two bushels of coal.[15]

Hours of the Distillatory Process	Quantity of Gas produced.
In the first hour	4,058
Second hour	3,028
Third hour	2,871
Fourth hour	2,526
Fifth hour	2,380
Sixth hour	1,971
Seventh hour	1,754
Eighth hour	1,450
	20,038

[15] Own Experiments.

The same heat as we have seen from the preceding table, [p. 79], which is necessary during the first hour of the operation, for the evolution of one hundred and fifteen cubic feet of gas, is required in the eighth hour for the production of no more than forty-two cubic feet, being a decrease in effect of nearly two-thirds.

When larger retorts are employed for decomposing coal in masses, from five to ten inches in thickness, the loss of heat is in a much greater ratio.

In the hope of remedying in some measure the evils thus distinctly ascertained to arise from the undue thickness of the masses of coal subjected to the distillatory process, there have not been wanting manufacturers who have had recourse to experiments on a large scale, to ascertain with certainty whether they might not be gainers by suffering the distillatory process, when the retorts are charged with two bushels of coal, to proceed only for the space of six hours, instead of eight. But the result of these experiments, as will be presently explained, has shown satisfactorily that it is more profitable to keep up the distillatory process for a period of eight hours, with the retorts fully charged, than to abridge the operation by terminating it at the end of six hours.

Others again, have imagined, that it would be more economical to decompose a less quantity of coal at once, or to decrease the thickness of the stratum of coal in the cylindrical, or in any of the before named retorts; but then again, serious difficulties occur in the practice. The more frequent charging of the retorts and luting on the covers,[16] which such a mode of operating require, occasions a prodigious waste of fuel, time and labour. A greater number of retorts and more workmen must likewise be employed, in order to produce the requisite quantity of gas daily, which the manufacturer is called upon to supply; more space of ground is required, and more dead capital must be sunk in the establishment. The more frequent and sudden alterations of temperature which the retorts necessarily suffer, by the more frequent introduction of cold coal, renders them extremely liable to become injured; and it is almost impossible to maintain a number of retorts thus worked, at an uniform temperature.

[16] When the cover is ground on, air-tight, the cost of the retort is much increased.

From various statements, which I have been favoured with, in confirmation of my own observations on the best method of working cylindrical retorts, it may suffice to lay before the reader the result of a series of operations instituted by one of the largest and best conducted establishments in this country; the public-spirited and indefatigable directors of which have done more in the way of extensive, costly, varied and long continued experiments, to improve the new art of lighting with gas, than any other similar body in the kingdom; and without whose exertions the gas light illumination would never have reached the state of perfection it has attained.

Report on a course of Experiments made to ascertain the comparative Economy [17] of manufacturing every week, 857,667 cubic feet of gas, by means of Cylindrical Retorts variously worked.

[17] The cost of materials and price of labour in this estimate, as well as in all subsequent statements, is given such as they actually were, at the time, when the experiments to which they refer were made.

Gas Light and Coke Company’s Works,
Westminster Station.

February 8th, 1819.

Sir,

Enclosed are the result of a series of experiments made under my direction with a view of ascertaining the relative value of the different modes of working cast-iron cylindrical retorts, from which you will perceive that it is more economical to work eight hours charges, as the workmen call it, that is to say, to suffer the distillatory process to go on for eight hours, when nearly two bushels of coal are contained in each retort, than to discontinue the operation at the end of six hours.

I am with respect,
Sir, Yours, &c.
T. S. Peckston.

To Mr. F. Accum,
Compton Street, Soho.

Process A.

Number of Days the Retorts were worked.	Number of Retorts in action.	Quantity of Coal decomposed for obtaining Gas.			Quantity of Coal used for Fuel.			Quantity of Gas produced.	Quantity of Gas from one Chaldron of Coal.
		Chaldron. Bushel.			Chaldron. Bushel.			Cubic Feet.	Cubic Feet.
Monday	87	10	-	30	4	-	24	94,987	8,768
Tuesday	88	14	-	24	6	-	8	128,597	8,784
Wednesday	88	14	-	24	6	-	8	122,188	8,331
Thursday	94	15	-	24	6	-	26	131,176	8,373
Friday	96	16	-	0	6	-	32	127,696	7,981
Saturday	96	16	-	0	6	-	20	127,536	7,971
Sunday	96	15	-	18	6	-	4	125,487	8,092
		103	-	12	43	-	14	857,667	8,300	[18]

[18] Average proportion of gas from a chaldron of coal.

Expenditure of Process A.

Coals, decomposed, 103 chaldron 12 bushel, at £ 2. 11s. 6d. the chaldron, (27 Cwt.)	£ 266	2	0
Small Coal, 43 chaldron, 14 bushels, used for fuel, at £ 2. 2s. the chaldron	91	2	4
Wages of two additional workmen (not required had the retorts been worked at eight hours charges,) at £ 1. 16s. each man, the week	3	12	0
Total expenditure,	£. 360	17	0

Products of Process A.

Coke, 103 chaldron, 12 bushel, at £ 1. 7s. the chaldron	£ 139	10	0
Breeze, or small coke, 6 chaldron, 9 bushels, at 18s. the chaldron	5	12	6
Tar, 7³⁄₄ tons, at £ 6. the ton	46	10	0
Ammoniacal liquor, 1864 gallons, at 1¹⁄₂d. the gallon	11	13	0
Gas, 857,667 cubic feet, at 15s. the thousand cubic feet	643	5	0
Total for products,	£ 846	10	6

Hence the amount of expenditure for procuring 857,667 cubic feet of gas, is £ 360. 17s.

The value of the saleable products £ 846. 10s. 6d.

And the average proportion of gas obtained from one chaldron of Newcastle coal, 8,300 cubic feet.

Process B.

Number of Days the Retorts were worked.	Number of Retorts in action.	Quantity of Coal decomposed for obtaining Gas.			Quantity of Coal used for Fuel.			Quantity of Gas produced.	Quantity of Gas from one Chaldron of Coal.
		Chaldron. Bushel.			Chaldron. Bushel.			Cubic Feet.	Cubic Feet.
Monday	57	9	-	18	2	-	13	94,987	10,000
Tuesday	77	12	-	31	3	-	8	128,597	10,000
Wednesday	73	12	-	8	3	-	2	122,188	10,000
Thursday	79	13	-	4	3	-	10	131,176	10,000
Friday	76	12	-	27	3	-	7	127,696	10,000
Saturday	77	12	-	27	3	-	6	127,536	10,000
Sunday	76	12	-	20	3	-	6	125,487	10,000
		103	-	12	21	-	16	857,667	10,000	[19]

[19] Average proportion of gas from a chaldron of coal.

Expenditure of Process B.

Coal, decomposed, 85 chaldron, 27 bushels, at £ 2. 11s. 6d. the chaldron	£ 220	16	10	¹⁄₂
Small Coal, 21 chaldron, 16 bushels, used for fuel, at £ 2. 2s. the chaldron	45	0	8
Total expenditure,	£. 265	17	6	¹⁄₂

Products of Process B.

Coke, 100 chaldron, at £ 1. 7s. the chaldron	£ 135	0
Breeze, or small coke, 3 chaldron, at 18s. the chaldron	2	14
Coal tar, 6 Tons, 8 Cwt. at £ 6. the ton	38	8
Ammoniacal liquor, 1536 gallons, at 1¹⁄₂d. the gallon	9	12
Gas, 857,667 cubic feet of, at 15s. the thousand cubic feet	643	5
Total for products,	£. 828	19

From the result of this process it appears, that at the expence of 265l. 17s. 6¹⁄₂; the value of the products obtained is £ 828. 19s.

By comparing the two preceding processes, A and B, it will be observed that the same quantity of gas was generated each day, notwithstanding there were fewer retorts in use, and less coal decomposed by process B, than by Report A, and that the expence of fuel, when the distillatory process was continued for a term of eight hours, was considerably less. Also, that the proportion of gas obtained from a chaldron of coals, was greater than when the process was continued for only six hours.

Hence, if from the products of

process A,	£. 846	10	6
we take the products of process B,	£. 828	19	0
The difference is,	£. 17	11	6

which, being subtracted from the difference between the expenditure, as specified in the process alluded to, namely

Process A,	£. 360	17	0
Process B,	265	17	6	¹⁄₂
The difference is	£. 94	19	5	¹⁄₂
Less	17	11	6
And leaves a balance of	£. 77	17	11	¹⁄₂

in favour of working eight hours charges, for one week, and producing a like quantity of gas, as had been obtained by working six hours charges.

Thus, having compared the quantity of coals actually used when working six hours charges, with what was used to produce a like quantity of gas from eight hours charges, I shall next point out, in process C, the quantity of gas obtained when working the same number of retorts for a period of eight hours which had been worked at the process of six hours.

Process C.

Number of Days the Retorts were worked.	Number of Retorts [20] in action.	Quantity of Coal decomposed for obtaining Gas.			Quantity of Coal used for Fuel.			Quantity of Gas produced.	Proportion of Gas to a Chaldron of Coals.
		Chaldron. Bushel.			Chaldron. Bushel.			Cubic Feet.	Cubic Feet.
Monday	87	16	-	18	3	-	22	165,000	10,000
Tuesday	88	14	-	24	3	-	24	146,667	10,000
Wednesday	88	14	-	24	3	-	24	146,667	10,000
Thursday	94	15	-	24	3	-	33	156,666	10,000
Friday	96	16	-	0	4	-	0	160,000	10,000
Saturday	96	16	-	0	4	-	0	160,000	10,000
Sunday	96	15	-	18	3	-	32	155,000	10,000
		107	-	0	26	-	27	1,070,000	10,000	[21]

[20] Worked at six hours charges in process A, [page 85], but here worked at eight hours charges.

[21] Average proportion of gas from a chaldron of coal.

Expenditure of process C.

Coal decomposed, 107 chaldron, at £ 2 11s. 6d. the chaldron	£ 275	10	6
Small coal, 26 chaldron, 27 bushels, used for fuel, at £ 2 2s. the chaldron	56	3	6
Total expenditure	£ 331	14	0

Products of process C.

Coke, 124 chaldrons, at £ 1 7s. the chaldron	£ 167	8	0
Breeze, or small coke, 4 chaldrons, at 18s. the chaldron	3	12	0
Tar, 8 tons, at £. 6 the ton	48	0	0
Ammoniacal liquor, 1945 gallons, at 1¹⁄₂d. the gallon	12	3	1	¹⁄₂
Gas, 1,070,000 cubic feet, at 15s. for a thousand cubic feet	802	10	0
Total for products	£ 1033	13	1	¹⁄₂

RECAPITULATION.

Products by process C.	£ 1033	13	1	¹⁄₂
Products by process A.	846	10	6
Difference	£ 187	2	7	¹⁄₂
Expenditure by process A.	£ 360	17	0
Expenditure by process C.	331	14	0
Difference	£. 29	3	0

From the above recapitulation it will appear, that by working equal numbers of retorts, at six and at eight hours charges, the balance is considerably in favour of the latter method; for, from the foregoing statement, there appears to be on the practice of the latter method an increase of saleable products amounting to

	£ 187	2	7	¹⁄₂
obtained at	29	3	0		less expence;
consequently there is a balance of	£ 216	5	7	¹⁄₂

in favour of working the retorts, as stated in process C, over that method shewn in process A; and in such proportion, let the number of retorts worked be what it may, an advantage will always be gained in this mode of manufacturing coal gas, by working the retorts at eight hours charges, as the workmen call it, in preference to adopting the shorter process.

From a series of operations made [22] with twenty parallelopipedal and with twenty cylindrical retorts, worked for one month, it has been ascertained that the decomposition of coal is most economically conducted when each retort is charged with 100 pounds of coal, and the distillatory process be continued for eight hours. Two men, one by day and one by night, can attend nine or ten retorts.