Electrification of the Atmosphere. 145 



In the present paper a number of experimental results are 

 ^iven relating to the electrification of gases surrounding metallic 

 bodies when these bodies and their surrounding atmospheres are 

 heated to a temperature below that of the melting point of zmc. The 

 paper is compiementan. to two published in the " Philosophical 

 Magazine,""* where, howe^•er, the electric state of the solid was con- 

 sidered. 



§2. Experimental Arrangement. 



To test the electric condition of the gases two arrangements 

 were used. 



In the first of these. Fig. IV., a metal tube (A), usually of 5 cm. 

 internal diameter of i"6 to^ 3'2 mm. in thickness, and of 82 cm. in 

 length, was used. Each end was closed with a tightly-fitting, 

 asbestos-covered cork, through the centre of which was passed a 

 wire or metal strip (M), so that it lay approximately in the axis of 

 the tube. This will be referred to as the axial wire. In addition, 

 each cork had a glass tube passing through it, the one in the cork 

 at the ingress end could be joined by rubber tubing to a glass wool 

 hlter (Fa), and a Woulffs's bottle (W), containing water or strong 

 sulphuric acid as the case might be ; the filter was always joined 

 metallically to the tube (A). 



To the glass tube at the egress end of (A) was joined a rubber 

 tube, which in turn led, through a "Woulff bottle (W,), to a glass tube 

 fitting into one end of a tunnel in a piece of parafiin. Another glass- 

 wool filter (F^,) was fixed on to the other end of the tunnel in 

 the same piece of paraffin, and to a second tunnelled piece. In the 

 other end of this second piece was fixed another glass tube, from 

 which a piece of rubber tube led to the air pump. The tube (A) 

 could be placed in a tube-heating furnace of the ordinary pattern. 

 In some experiments the tube (A) was exposed directly to the flame; 

 in others it was covered with asbestos and wire gauze. 



In the second arrangement, tube (A) was replaced by two cylin- 

 drical vessels of iron, Fig. V., about 15cm. in diameter, the lower 

 30 cm., the upper 10 cm. in height. The upper telescoped into 

 the lower, and thus formed an hermetically-sealed lid. At a height 

 of 3"8 cm. from the bottom of the lower and diametrically opposite 

 to each other were fixed two iron tubes (A) and (B), each about 

 45 cm. long and i'2 cm. internal diameter. Through the middle 

 of the lid was passed a stout brass wire ("W), surrounded and insu- 

 lated from the lid by ebonite wrapped in asbestos, great care being 

 taken to make the fitting air-tight. The end (E) of the brass wire 

 carried a thin disc of zinc, 10 cm. in diameter. A second disc 

 of zinc was laid on the inside of the bottom of the lower vessel. 

 The tubes (A) and (B) were closed at the ends remote from the 

 cylinders by tightly-fitting corks, each supplied with a glass tube 

 leading by rubber tubing to various filters and wash-bottles as in 

 the first arrangement. Asbestos was placed on the sides and on the 



*" Phil. Mag." ser. 5, vol. xlviii., pp. 97-106 (July 1899) ; 

 " Phil. Mag.," ser. 6, vol. i., pp. 442-454 (.A.pril 1901). 



