ELECTRIFICATION OF AIR, VAPOUR OF WATER, AND OTHER GASES. 211 



Similar numbers were got when the air was electrified positively. 



For carbonic acid gas, electrified positively and negatively, the same filters gave 



n = 0-82 (filter AB), 

 ri = 0'42 (filter A'B'). 



57. We now used the filter (n = 077) for determining electric density of 

 electrified air or gas. A known volume of the electrified gas ( 47) was sucked 

 through the filter in connection with an electrometer whose constant was determined 

 as in 1.8 (0'154 C.G.S. electrostatic quantity per 100 divisions deflection). We 

 thus found 



(1.) For air electrified, positively or negatively, by six needles at a potential of 

 5000 volts, an electric density of 0'92 X 10~ 4 C.G.S. per cub. centim. 



(2.) For air electrified, positively or negatively, by electrified gas flame at a 

 potential of 5000 volts, an electric density of 1'98 X 10" 1 C.G.S. 



(3.) For carbonic acid gas, electrified negatively by gas out of a cylinder lying on 

 its side ( 54), or positively by six needle points at a potential of 50CO volts, an 

 electric density of 2 '4 X 10 ~* C.G.S. 



58. We now set about to definitely determine the relative efficiencies of various 

 forms of filters. A standard filter of block-tin pipe, 4 centims. long and 1 centim. 

 bore, with 6 brass gauzes and 5 plugs of cotton wool was used, and it was per- 

 manently kept in metallic connection with electrometer, E'. The filter to be tested 

 was joined to electrometer, E. Air electrified positively or negatively was sucked 

 through in one direction, passing through the tested filter first, and then through 

 the standard filter, the diselectrifying power of which was 077 for electrified air. 

 Hence it is possible to determine the diselectrifying power of the tested filter by 14. 

 Thus, from the numbers in the following section, we get for the diselectrifying power, 

 for positive electricity, of the 7 millim. brass tube the least effective of those 

 mentioned n = 1 -r- (1 + 4/077) O'lG; and for the block-tin pipe, 90 centims. 

 long, and coiled into a spiral n = 1 -r (1 + 0'63/077) = 0'55. 



59. Let q z = quantity of electricity taken out by the standard filter of block-tin 

 pipe with six brass gauzes and five plugs of cotton wool ; and 



(ft = the quantity of electricity taken out by the tested filter from the air before 

 passing the standard filter. A long series of experiments with no wire gauze or 

 cotton wool in the tested filters is summarised in the following tables. The potential 

 of the machine was in each experiment 10,000 volts. 



2 E 2 



