HORIZONTAL ROTARY RETORT.

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least but in a small quantity. One gallon of coal taryields 15 cubic feet of olifiant gas, which greatlyincreases the illuminating power of the carburettedhydrogen.

From what has been so far stated, it will beunderstood why one chaldron of Newcastle coal,when decomposed by the new process, mayreadily be made to produce from 15,000 to 18,000cubic feet of gas and upwards, whereas the samequantity of coal, if decompoed by the old method,yields only upon an average 10,000cubic feet ofgas.*

In the former case, the greater part of the essen-tial oil and tar which the coal would have affordedis decomposed, as stated already by virtue of thehigh temperature to which the vapourous tar issuddenly exposed in the horizontal rotary retort,which is not the case when coal is decomposed inthe retorts of the old construction.

Gain in the quantity of coke .—With the cylin-drical or cast-iron retorts of the old shapes, the quan-

* The experiments exhibiting the maximum quantity of gasobtainable from coal, see page 44, were made with the horizontalrotary retorts at the Royal Mint. Similar results have also been ob-tained at the Westminster Gas-Works.

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