4q8 



NATURE 



[March 21, 1895 



water-dropper electrifies. Thus curve (I) was obtained from 

 the ordinal)' air of the laboratory in the vai, and curve (2) after 

 the aspirator was working for some time. In this curve the 

 water-dropper ilsf If was running for seme time before the first 

 observation was taken. The other curves were obtained after 

 ftirther continuous working of the aspira'or. 



After curve (4) was obtained the aspirator was worked 

 contioDously for iwenly-five hours, and then curve (5) was 

 obtained. 



§ 10. At the end of twenty-three days of October and 

 November 1894 (;:§ S, 9, above), when the air inside the vat 

 must have been fan ly free from dust, and when the water dropper 

 of itself was giving little negative electrification, we bubbled air 

 into it by a forked tube, one end of which was connected to a 

 bellows, and three other open ends were below the water inside 

 the vat. In five experiments thus made^ — two on November 7, 

 two on November S, and one on December 17, an average 

 negative electrification of 5 volts in twelve minutes was 

 obtained. 



S II. We now arranged a U-t»be with pure water in it 

 (Fig. 4) outside the vat. Air from the bellows bubbled 



through the water in this U, and was carried thence by a 

 block-tin pipe into the vat without any further bubbling. 

 Observations by the f|uadrant electrometer, while the water- 

 dropper nas running and the bellows worked, gave us measure- 

 menU of the varying stale of the electrification of the air in 

 the vat. The average of fifteen experiments gave a negative 

 electrification of the air in the vat of SJ volts in 25 minutes. 

 The rale at which the air was blo-*n in in these experiments 

 was such as to displace the entire' volume of air in the vat in 

 half an hour. 



% 12. Curve (8) shows the rate of electrification of air, in 

 one of the fifteen experiments, when thus bubbled through the 

 water in the U-lube and then admitted into the val. 



§ 13. Two (J-tubci, in series, wiih water in each, did not 

 iccm to give a perceptibly cumulative effect. 



S 14. The effect of one or more wire gauze strainers between 

 the U-iube and the vat, or between the U-tube and the bellows, 

 wai next test. d. The gauzes were placed between short lengths 

 of lead tul«, which were held together by a rubl.cr tube slipped 

 over therri. The arrangement is shown by longitudinal and 

 cross sections in I-'ig. 5. Twelve wire gauzes, with or without 



cotton-wool between them, placed between the bellows and the 

 U-tube, did rot prevent the subsequent electrification by bub- 

 bling of the air thus filtered. But when placed between the 

 U-tube and the vat they almost entirely di.-electrified the air, even 

 without the cotton-wool, and still more decidedly when cotton- 

 wool was loosely packed between the wire gauzes. A single 

 wire-gauze strainer produced but little of dis-elecirifying effect. 

 § 15. The interpretation of these experiments is complicated, 

 and the lime required for each is lengthened, on account of the 

 large mass of air in the vat to start with, whether uncharged 01 

 retaining electricity from previous expeiimenis, and also on 

 account of the effect of the water-dropper itself. Hence, in 

 our later experiments, we fell b.ick on the arrangement shown 

 in Fig. 2, by which we test the electrification of the liquid, and 

 not directly that of the gas blown through it. 

 . § 16. In our first experiment with this apparatus the 

 ( amount of the electrification did not seem much affected 

 when a paper cover was put on the beaker, or when we 

 tilted the beaker as shown in Pig. 3. We now made a 

 large number of tests with dilTcrent covers and screens 

 (chiefly of sheet copper or sheet zinc, or brass wire gauze) at 

 difi^erent heights above the liquids, .ind we concluded that, if the 

 screens are not within a centimetre and a half of the liquid sur- 

 f.ice, they Jo not directly affect the magnitude of the electrifica- 

 tion obtained. In nearly all of the subsequent experiments a hori- 

 zontal circular screen of thin sheet copper, leaving an air space 

 of about 3 mm. all round between its edge and the inner sur- 

 face of the jar, about 3 cm. above the liiiuid surface, was used 

 to prevent spherules of the liquid from being tossed out of the 

 jar by the bubbling. 



§ 17. In the following short summary of our results the dura- 

 tion of each experiment was ten minutes. The efltect of blowing 

 air through water and other liquids is summarised in !;§ 18 to 



NO. 1325. VOL. 51] 





Lead-. 



India Rubber- 



Fio. 5. 



27, and of blowing other gases than air through waterjin §§ 28 

 to 31. 



§ 18. The jar contained 200 c.c. of the Glasgow town-supply 

 water (from Loch Katrine). A mean of seventeen experiments 

 showed an electrification of the jar to four volts positive when 

 air was blown through it for ten minutes. 



§ 19. A solution of zinc sulphate of different strengths was 

 now used instead of the pure water. Three experiments, with 150 

 c.c. of water containing one drop of a saturated solution of the 

 zinc sulphate, gave half the positive electiihcation that would, 

 under similar circumstances, have been obtained from water 

 only. With live drops no definite electrification was olitained. 

 \\ iih greater proportions of the zinc sulphate solution up to 

 saturation (twenty-four experiments altogether) the electrifica- 

 tion was on the average slightly negative. 



§ 20. Twelve experiments were then made to test the effect of 

 adding a solution of ammonia to the water. One drop reduced 

 the electrification to one-half; two drops brought it down to 

 <pne-quartcr. With larger proportions of ammonia than this, 

 up to a saturated solution, we found a veiy slight positive 

 electrification, never amounting to more than a small fraction of 

 a volt, and therefore negligible in the circumstances. 



§ 21. Seven experiments with sulphuric acid of different 

 strengths all showed small /u-ti/rr'^ electrification, the amount 

 gradually decreasing from \ volt, in ten minutes, with o'5 per 

 cent, acid in water to ,',.. volt, in the same time, with acid o£ 

 full strengih. 



Seven experiments with hydrochloric acid solution of different 

 strengths all showed a small tiCj;alhe elcctrificaiion, the amount 

 gradually increasing from \ volt, in ten minutes, with \ per 

 cent, acid solution in water to ij volts, in the same time, with 

 acid solution of full strength. 



Nine experiments with calcium chloride solution were made. 

 A saturated solution and a solution diluted to 75 per cent, of 

 full strength gave no result ; but solutions of gradually 

 diminished strength, from 50 per cent, down to ,'„ per cent., 



