English: Swan has done much towards the perfection of glow lamps. Long before Edison, he tried to obtain more durable carbon filaments. Too little attention had been paid by other experimenters to the exhaustion of the vessel containing the carbon, and also to the diminution of resistance at the ends of the carbon connected with the platinum wire. Fig. 439 shows a lamp by Swan. The platinum wires are carefully fused into a little glass tube ending in two loops outside. The lower portion consists of gutta-percha which has a glass screw, by means of which the lamp might be screwed upon any ordinary gas-arm after removal of the burner. Each of the platinum hooks is connected with one of the keys. The carbon is ten centimetres long, and is prepared from cotton fibres soaked in sulphuric acid (2 parts acid to 1 part water) ; they undergo a similar change to paper when similarly treated, i.e. artificial parchment is obtained. The fibre, which after the treatment is more tenacious, is bent into the form required, and is placed in a crucible filled with fine coal-dust, hermetically closed and exposed to heat The carbons are fastened to the platinum wires in the following manner : Their ends are made to overlap, and are bound together by cotton, which again is carbonised.