292 Rev. P. J. Kirkby : Chemical Effects of the 



was fused together round a piece o£ iron wire a which carried 

 the zinc cathode wdiose diameter was about 2 cms. Iron was 

 used instead of platinum to avoid the chemical effects which 

 might arise if the cathode became hot and heated the platinum 

 sufficiently (P. J. Kirkby, Phil. Mag. Oct. 1905). The glass 

 did .not stick perfectly to the iron, but the joint was made 

 thoroughly air-tight by placing some mercury above it in a 

 piece of rubber tubing as shown in fig. 1. The anode, near 

 the point B of the figure, was also of zinc *, its diameter was 

 2 cms., and it was supported by one end of an iron rod which 

 passed up through the glass tubing and w^as bent at the 

 bottom so that its other end E protruded above the mercury 

 in the jar. At the point C, inside the glass tube, was a steel 

 guide, fixed by springs to the inner wall of the glass tube. 

 By raising or lowering the end E the anode B could be 

 adjusted at any distance from A not exceeding 16 cms. A 

 piece of glass tubing of large bore, fixed horizontally, led 

 from a place in the vertical tube AD near the cathode A into 

 the vessel F containing pentoxide of phosphorus, and per- 

 mitted the water- vapour, as it was formed, to disappear 

 rapidly. Glass tubing connected F to G, another drying 

 vessel, which was similarly connected to two McLeod gauges 

 (only one is show r n in the fig.) and an ordinary manometer 

 (not shown), which enabled any pressure to be measured. 

 All these, which were in permanent connexion, were con- 

 nected by a single tube to a large mercury pump; but the 

 tube leading to the pump could be closed by a stopcock H, 

 which thus greatly reduced the space where the falls of 

 pressure were measured and so increased the accuracy of the 

 measurements. 



Hydrogen and oxygen were generated together by the 

 electrolysis of pure barium hydrate contained in a small 

 sealed glass vessel which was provided with a U-shaped 

 manometer ; were passed on through the stopcock K to a 

 drying chamber, and then were admitted by the stopcock J 

 to the mercury pump and by H to the rest of the apparatus. 

 Every joint was of sealed glass, and the stopcocks and the 

 vessel G were protected by mercury so that every part of 

 the apparatus was thoroughly air-tight. By working the 

 pump with the stopcock H open and so evacuating the ap- 

 paratus, and then by replenishing it with pure mixed gases, 

 the air or gas vitiated by use could be eliminated to any 

 desired extent. 



* Zinc electrodes were used because they are most easily worked; 

 and I have shown that the effects under investigation are independent 

 of the material of the electrodes. 



