ELECTRIFICATION OF AIR, VAPOUR OF WATER, AND OTHER GASES. 213 



formulae in 12. That of the block tin was thus found to be 0'93 for negative 

 electricity and 0'9 for positive, and that of the glass nearly the same, 0'9 for negative 

 and 0'84 for positive. The block-tin filter contained 18'927 grms. of wire. 



G2. The next filter tried was a block-tin pipe, 10 centims. in length and 1 centim. 

 in diameter, containing 8 '3 3 grms. of clean, very fine brass filings, enclosed at each 

 end by a plug of cotton-wool and a piece of brass gauze. These brass filings, which 

 were got from a brass-finishing workshop, were poured into a glass tube about 4 feet 

 long and about three-quarters full of water. The filings and water were well shaken 

 up, and the tube was then allowed to stand for several hours, so as to give the filings 

 time to settle. After washing the filings three times in this manner, the top portion 

 was taken off and dried before a fire, and used for filling the filter. It was found that 

 when the electrified air passed through this filter of brass filings, before it passed 

 through the copper-wire filter attached to electrometer, E, no deflection was obtained 

 on the latter. This showed that the brass-filings filter deprived the air of practically 

 all its electricity. We tried also a filter with sawdust instead of brass filings, but its 

 efficiency was comparatively low. 



FILTER OF BRASS FILINGS USED TO FIND EFFECTS OF SPIRIT FLAME, COAL GAS 

 FLAME, AND HYDROGEN FLAME IN ELECTRIFYING AIR ( G3-6G). 



63. Having found the brass-filings filter thoroughly satisfactory, we used it to 

 investigate the effect of various kinds of flames in electrifying air. First of all, we 

 electrified the air of the laboratory by means of an insulated spirit flame, joined to 

 the insulated positive terminal of a Voss electric machine. The machine was worked 

 for 40 minutes, and then, 2 minutes after it was stopped, the electrification of the 

 air in the vicinity was tested by drawing some of it through a tube leading to the 

 brass-filings filter, joined to electrometer, E, The pump was worked at the rate of 

 1 stroke per 4 seconds, and after 200 strokes the electrometer read 174 divisions, or 

 about 3'3 volts positive. After the lapse of half-an-hour, the air of the laboratory 

 was found to be still strongly charged with positive electricity. 



64. Removing the water vessel from below the glass cylinder, C, in fig. 7, and 

 substituting for it a metal plate kept in metallic connection with the sheath of the 

 electrometer and the disinsulated terminal of the machine, we kept a coal-gas flame 

 burning within the glass cylinder, while the machine and pump were worked and obser- 

 vations taken by electrometer, E, and filter, AB. With the machine at 10,000 volts, we 

 found that, after two or three strokes of the pump, the deflection was about 500 scale 

 divisions, positive or negative, according as the machine was positive or negative. 

 This gives ( 13) for the electric density, per cub. centim., 11 X 10~* C.G.S. electro- 

 static, which is much greater than any of our previous results ( 23, 57). 



65. To burn hydrogen, the burner, G of fig. 7, was made of rolled platinum foil 

 with a fine nozzle, which was kept in metallic connection with the insulated terminal 

 of the electric machine. The hydrogen gas was generated from zinc and dilute 



