of Substances upon Voltaic Action. .':-J .453 



103 observations they were absent, bat the results obtained 

 only confirmed the previous ones. 



Exclusion of Air-Bubbles, fyc. 



Bubbles of air, which had caused considerable disturbance 

 of the current, and which, owing to the narrowness of the 

 spaces round the electrodes, were difficult to remove, were at 

 a later period of the research perfectly excluded by the fol- 

 lowing means : — A few minims of the liquid, sufficient only 

 to fill the annular space, were poured into each dry empty 

 tube before placing it in the frame, and allowed to trickle 

 very slowly down the inclined tube and displace the air ; if 

 this did not succeed it was run back into the bulb and poured 

 again, and the action repeated with shaking if necessary until 

 all air was expelled; the opposite end was then treated 

 similarly, and the bulb filled and the tube placed in the 

 frame. Bubbles of hydrogen, due to corrosion of zinc, and 

 the formation of insoluble subsalts of zinc, were prevented 

 by employing a suitable electrolyte. The most improved 

 liquid consisted of 750 c.c. of thoroughly boiled distilled 

 water, 2990 grains of ordinary zinc sulphate, the solution 

 filtered, and 25 c.c. of similar boiled water saturated with 

 chlorine added to it. 



Prevention of Leakage of Liquid. 



To obviate any disturbance or want of insulation by leakage 

 of solution, the bar of wood which supported the tubes was 

 thoroughly varnished ; but even when a large number of 

 "tubes slightly leaked, the essential effects were clearly dis- 

 tinguishable. Leakage of liquid was, however, entirely 

 prevented at a later period by the following method : — The 

 ends of the dry tubes were coated inside with thick petroleum 

 black varnish and allowed to dry ; shellac was then melted 

 upon the corresponding parts of the wires and thoroughly 

 fused when the wires were in the tubes ; and after coolino- 

 the junctions were thickly coated with the same varnish and 

 allowed to dry ; the elasticity of the varnish prevented any 

 cracking or separation of the rigid shellac. 



Incidental Circumstances. 



It was fully proved in various ways, and by several special 

 series of experiments and observations, that the movements 

 of the galvanometer-needles were not perceptibly due to the 

 placing or removal of heavy bodies, nor to air-currents, the 

 influence of light, or of magnets or articles of iron near 

 the galvanometer, &c. 



