The chief impurity of peat-gas is carbonic acid: this amounts to 25 to 30 per cent. of the gas before purification, and if the peat be insufficiently dried, it is considerably more. The quantity of slaked lime that is consumed in purifying, is therefore much greater than is needed for coal-gas, and is an expensive item in the making of peat-gas.

While wood-gas is practically free from sulphur compounds and ammonia, peat-gas may contain them both, especially the latter, in quantity that depends upon the composition of the peat, which, as regards sulphur and nitrogen, is very variable.

Peat-gas is denser than coal-gas, and therefore cannot be burned to advantage except from considerably wider orifices than answer for the latter, and under slight pressure.

The above statements show the absurdity of judging of the value of peat as a source of gas, by the results of trials made in gas works arranged for bituminous coal.

As to the yield of gas we have the following data, weights and measures being English:—

100 lbs. of peat of medium quality from Munich, gave Reissig303 cub. ft.
100 lbs. of air-dry peat from Biermoos, Salzburg, gave Riedinger305 cub. ft.
100 lbs. of very light fibrous peat, gave Reissig379 to 430 cub. ft.
100 lbs. of Exter's machine-peat, from Haspelmoor, gave367 cub. ft.

Thenius states, that, to produce 1000 English cubic feet of purified peat-gas, in the works at Kempten, Bavaria, there are required in the retorts 292 lbs of peat. To distil this, 138-½ lbs. of peat are consumed in the fire; and to purify the gas from carbonic acid, 91-½ lbs. of lime are used. In the retorts remain 117 lbs. of peat coal, and nearly 6 lbs. of tar are collected in the operation, besides smaller quantities of acetic acid and ammonia.

According to Stammer, 4 cwt. of dry peat are required for 1000 cubic feet of purified gas.

The quality of the gas is somewhat better than that made from bituminous coal.

18.—The examination of Peat as to its value for Fuel, begins with and refers to the air-dry substance, in which: