336 Lord Kelvin and Messrs. Maclean and Gait. [Feb. 21, 



platinum wire, with one end touching the pumice, connected it to the 

 insulated electrode of a quadrant electrometer. A metal can, M, 

 large enough to surround both branches of the U'^ube without 

 touching either, was placed so as to guard the tube from electric 

 influences of surrounding bodies, the most disturbing of which is 

 liable to be the woollen cloth sleeves of the experimenters or observers 

 moving in the neighbourhood. This metal can was kept in metallic 

 connection with the outside metal case of the quadrant electrometer. 

 The length of the exposed platinum wire between the \J -tube and 

 the electrometer was so short that it did not need a metal screen 

 to guard it against irregular influences. An india-rubber tube from 

 an ordinary blow-pipe bellows was connected to the uninsulated end 

 of the U -tube. Air was blown through it steadily for nearly an 

 hour. With the pumice soaked in strong sulphuric acid in the other 

 branch, the electrometer reading rose in the course of three-quarters 

 of an hour to about 9 volts positive. When the pumice was moistened 

 with water, instead of sulphuric acid t no such effect ivas observed. The 

 result of the first experiment proves decisively that the passage of 

 the air through the (J'^be gave positive electricity to the sul- 

 phuric acid, and therefore sent away the dried air with negative 

 electricity. A corresponding experiment with fragments of pure 

 chloride of calcium instead of pumice in sulphuric acid, gave a 

 similar result. In repetition of the experiments, however, it was 

 noticed that the strong positive electrification of the (J-tube seemed 

 to commence somewhat suddenly when a gurgling sound due to the 

 bubbling of air through free liquid, whether sulphuric acid or 

 chloride of calcium solution in the bend of the Ll'tube began to be 

 heard, It has since been ascertained that it was because no liquid 

 accumulated in the bottom of the JJ-tube that no electric effect was 

 found when the pumice was moistened with pure water. 



3. Arrangements were made to prevent any bubbling of the air 

 through liquid, by using a straight tube instead of a \J -tube. In a 

 large number of experiments with pumice, moistened with pure sul- 

 phuric acid, in the straight tube, and air blown through for about 

 half an hour, no definite electrification was obtained. In this 

 straight tube, as formerly with the (J -tube, pumice moistened with 

 pure water gave no electrification. Chloride of calcium in lumps, 

 not specially dried, gave no effect in the straight tube ; but if 

 previously heated to 180 or 200 and put into the straight tube 

 when still hot, it gave an enormous positive electrification imme- 

 diately on the commencement of blowing. Strong positive electrifi- 

 cation was obtained a second time, by discharging the electrometer 

 to zero, re-insulating, and re-commencing the blowing. But after 

 discharging a second time, re-insulating, and re-commencirig the 

 blowing, no further electrification was found. 



