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With the detecter this is avoided, as a large flame can be used, which is considered by some a preferable means of testing for small quantities; and the test can be made without risk. Where gas is present in large quantities, the blue flame at the end of the test tube will be found a further proof. This latter result is produced by the slightest compression of the ball.
The detecter, on account of its size, can be placed in a break in the roof where an ordinary lamp even a small Davy could not be put, and a purer sample of the suspected atmosphere is obtained than would be the case even a few inches below the level of the roof, 2.
Out of twenty-eight tests in a mine working a long-wall face the Davy showed gas only eleven times, while the detecter showed it in every case. The detecter, as will be perceived from the one exhibited, and the accompanying sectional drawing, consists simply of an oval-shaped India rubber ball, fitted with a mouthpiece.
Being able at will to force the contents of the detecter on to the flame, the effects of an explosion inside the lamp need not be feared. The use of the detecter will permit the further protection of the present tin shield lamp, by an extra thickness of gauze, if such addition is found advantageous in resisting an increased velocity. 7.
The detecter supplies a better knowledge of the condition of the working places, especially in breaks and cavities in the roof; which latter, with the help of a nozzle and staff, may be reached to a height of ten feet or more, by the detecter being pressed against the roof and sides, or by the use of a special form of detecter. 5.
Now, a flaw, a hideous flaw, in the soi-disant detecter of flaws, a ridicule in the exposer of the ridiculous that is fatal; and I am surprised that Lee, who wrote a folio against Locke in his lifetime, and other examiners, should have failed in detecting this.
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