This beautiful property of spongy platinum was happily applied to the construction of lamps for producing an instantaneous light. The form given to the lamp by Mr. Garden of London is shown in the annexed figure, where AB is a globe of glass, fitting tightly into another glass globe CD by a ground shoulder _m n_. The globe AB terminates in a hollow tapering neck _m n o p_, on the lower end of which is placed a small cylinder of zinc _o p_. A brass tube _a b c_, is fitted at _a_ into the neck of the globe CD, and through this tube, which is furnished with a stop-cock _d_, the gas can escape at the small aperture _c_. A brass pin _c f_, carrying a brass box P, is made to slide through a hole _h_, so that the brass box P, in which the spongy platinum is placed, can be set at any required distance from the aperture _c_. If sulphuric acid, diluted with an equal quantity of water, is now poured into the vessel AB by its mouth at S, now closed with a stopper, the fluid will descend through the tube _m n o p_, and if the cock _d_ is shut, it will compress the air contained in CD. The dilute acid thus introduced into CD will act upon the ring of zinc _o p_, and generate hydrogen gas, which, after the atmospheric air in CD is let off, will gradually fill the vessel CD, the diluted acid being forced up the tube _o p m n_, into the glass globe AB. The ring of zinc _o p_ floats on a piece of cork, so that when CD is full of hydrogen, the diluted acid does not touch the zinc, and consequently is prevented from producing any more gas. The instant, however, that any gas is let off at _c_, the pressure of the fluid in the globe AB, and tube _m n o p_, overcomes the elasticity of the remaining gas in CD, and forces the diluted acid up to the zinc _o p_, so as to enable it to produce more gas to supply what has been used. The lamp being supplied with hydrogen in the manner now described, it is used in the following manner. The spongy platinum in P being brought near _c_, the cock _d_ is turned, and the gas is thrown upon the platinum. An intense heat is immediately produced, the platinum becomes red-hot, and the hydrogen inflames. A taper is then lighted at the flame, and the cock _d_ is shut. Professor Cumming, of Cambridge, found it necessary to cover up the platinum with a cap after every experiment. This ingenious chemist likewise found, that, with platinum foil the 9,000th part of an inch thick kept in a close tube, the hydrogen was inflamed; but when the foil was only the 6,000th of an inch thick, it was necessary to raise it previously to a red heat.