Producing 8000 cubic feet of gas, from the chaldron of Newcastle coal.
| Eighty-five retorts, once replaced at £. 15 each | £. 1275 | 0 | 0 | |||
| Deterioration of grate bars, fire shovels, tongs and rackers | 117 | 16 | 0 | |||
| 4653 chaldron of coals for obtaining the gas, at £ 2. 8s. the chaldron | 11,167 | 4 | 0 | |||
| 11633⁄4 chaldron of coal for fuel, at £ 2. 1s. the chaldron | 2385 | 13 | 9 | |||
| Eighteen men at £ 1. 6s. each manthe week, being nine for the day, and nine for the night | 1216 | 16 | 0 | |||
| £. 16,162 | 9 | 9 | ||||
| From which deduct 4653 chaldron of saleable Coke, at £. 1 3s. the chaldron | £. 5350 | 19 | 0 | |||
| 11633⁄4 chaldron of small coke, or breeze, at 10s. the chaldron | 581 | 17 | 6 | |||
| £. 5932 | 16 | 6 | ||||
| Cost of obtaining 37,230,000 cubic feet of gas, according to process B, | £. 10,229 | 13 | 3 | |||
| Deduct the cost of Process A, | 9174 | 12 | 3 | |||
| Balance in favour of Process A. | £. 1055 | 1 | 0 | |||
The reader will have no difficulty in calculating from the preceding experiments, every variation which can possibly take place, as to the degree of temperature most economically to be employed in consequence of a variation in the prices of coal, coke and labour.[27]
[27] The average cost at which coal gas can be manufactured on a large scale in London, is seven shillings the thousand cubic feet, deducting not only the interest of the capital sunk in erecting the establishment, rent and taxes, the cost of the coal, labour, wear and tear of the machinery, and superintendence, but all other necessary and incidental expences that may occur.
Comparative facility with which the decomposition of different species of Coal is effected.
The temperature necessary for the decomposition of different kinds of coal, varies. Some species of coal are more readily decomposed, and require a less portion of fuel than others; they yield up their maximum quantity of gas, in an almost equal stream from beginning to end, and no extraordinary increase of temperature is required to terminate the distillatory process. Other kinds of coal require a different treatment; the temperature necessary to complete their decomposition requires that the heat should be considerably increased as the process advances; and without this condition the evolution of the gas would cease altogether.
A striking proof of this statement may be seen when Newcastle or Sunderland coal are attempted to be decomposed at a temperature which is sufficient for the decomposition of Scotch Splent coal, or Lancashire Wiggan coal.
The decomposition of the latter, will be fully effected when the distillatory vessel exhibits to the eye a dull cherry redness, and the evolution of the gas at such a temperature will take place in torrents from beginning to end. In order, on the other hand, to complete the decomposition of Newcastle and Sunderland coal, the heat must be increased as the process proceeds, and the production of the gas will be extended far beyond the time required for decomposing a like quantity of Scotch, or Lancashire Wiggan coal, when exposed to the same degree of heat.
It must be allowed, however, that few experiments have been yet made on this subject. I have reason to believe that all those varieties of coal which afford an incoherent friable coke, are decomposed at a much lower degree of heat, than such as produce, when treated under like circumstances, a ponderous compact coke. And if we give credit to the assertion of those workmen, whose business it is to manufacture a given quantity of gas by means of a certain quantity of coal delivered to them, it would appear that coal which affords gas abounding in sulphuretted hydrogen, is the kind of coal most easily to be decomposed. This, as far as it regards the decomposition of Scotch Splent or cannel coal, is certainly true. No species of coal affords gas at a lower temperature, and of none is the gaseous product more loaded with sulphuretted hydrogen gas. The subject is important and deserves to be pursued; particularly in places where coke is not, as it is in the metropolis, and all places where coal bears a high price, next to gas, the primary article to which the attention of the manufacturer of coal gas ought to be directed.
The following are the result of a series of experiments on the subject made at the Westminster Gas Works,[28] the same temperature being employed throughout the process.