Fig. 8.—An interesting hydrogen experiment.
Preparing hydrogen by the foregoing method is inconvenient and expensive if any quantity is to be collected, and so in this case the following plan is usually adopted:—Support a flask (A, [Fig. 8]), and place zinc chips (B) in it to the depth of about 1⁄4 inch. Fit the mouth with a cork, through which passes a delivery tube (C) and a “thistle” funnel (D), dipping nearly to the level of the zinc. When the gas is required, dilute sulphuric acid—one part oil of vitriol to ten parts water—is poured down the funnel until the flask is about one-third filled (E).
Five or ten minutes should be allowed after bubbling has commenced before an attempt is made to light the gas at the delivery tube, as otherwise air from the flask may be intermingled in the exact proportion to cause a bad explosion. No danger need be feared if several minutes are allowed for the air to be thoroughly dispelled, or, as an additional measure of safety, a damp towel (F) is wrapped round the flask to prevent scattering of the glass in the event of a mishap. The glass delivery tube should have been softened in a spirit flame and drawn to a fine point where the hydrogen issues. The gas will be found to burn with an almost colorless flame.
If a glass tube (A) of larger bore than the delivery pipe be slid over this latter while the gas burns, a peculiar musical note is produced—hollow-sounding and shrill ([Fig. 9]). It is caused by the rapid succession of slight explosions which constitute the combustion of hydrogen.
Fig. 9.—A musical flame.
The extreme lightness of hydrogen, as well as its combustibility, is well illustrated by blowing a soap bubble. Connect a clay pipe with the glass delivery tube by means of a length of india-rubber tubing, and provide this latter with a small clip—tie-clip, for example—so that the gas supply may be shut off at will ([Fig. 10]). Let the hydrogen pass for a minute or so, to clear air out of the clay pipe, and then, having shut off the gas, dip the pipe bowl into soap-suds. Next open the clip until the hydrogen has blown the bubble large enough, and then shut off, shaking the shimmering globe free. It will rise very quickly, just like an unballasted balloon, and if a lighted taper be applied to its surface it will explode to annihilation with a loud report.
Fig. 10.—To explode a soap bubble.