16 Prof. R. Threlfall on the Electrical 



(1) Solution of potassium hydrate in tube 4 feet long. 

 *(2) Tube 18 in. long, first half filled with metallic anti- 

 mony, second half filled with clean silver foil. 



(3) U-tube 12 x 1 in., solution of silver nitrate. 



(4) U-tube 12 x 1 in. ; solid potash. 



(5) 2 ditto,, sulphuric-acid beads. 



(6) 1 bottle, phosphorus pentoxide. 



(7) 2 U-tubes, ditto. 



All the connexions were of glass throughout, but it was 

 found convenient to use several rubber stoppers coated with 

 hard paraffin. The distillation of the pentoxide was carried 

 on in a porcelain tube 2 centimetres in diameter and nearly 

 a metre long, the connexions being made with glass tubes 

 pushed into the ends of the porcelain tube, and packed with 

 glass-wool and some pentoxide. This packing is very firm 

 and good. The first three quarters of the porcelain tube 

 were nearly filled with pentoxide, the last quarter contained 

 platinized porcelain and asbestos, the latter most carefully 

 purified by boiling in hydrochloric acid and strong heating. 

 The distillation was carried on in some cases so as to cause 

 the pentoxide to condense in the tubes and vessels in which 

 it was to be used, and a considerable quantity was also 

 collected in a bottle. 



The final product passed all the tests I have enumerated, 

 and was used throughout the nitrogen apparatus, even for 

 drying the pump, lubricating the taps, &c. Of course a good 

 many tubes full of pentoxide were distilled, and nearly three 

 months were consumed in obtaining the final product. If I 

 had not had the assistance of Mr. J. A. Pollock in this work, 

 I have an impression that I might be at it still. The com- 

 mercial pentoxide was used in this work, for the substance 

 we prepared ourselves was probably good enough for most 

 purposes as it was. I have sometimes wondered whether ex- 

 perimenters who have of late used so much pentoxide for 

 critical work on gases have recognized the necessity of testing 

 the product obtained by distilling the pentoxide in oxygen. 

 In my experience, unless the oxygen stream be very strong it 

 is quite possible to fail to remove the last traces of free 

 phosphorus. 



Sulphur f. — I happened to have some very pure sulphur 

 which had been prepared for another purpose. It will be 



* It was found as the result of several preliminary experiments that 

 metallic antimony is a rather good absorber of chlorine, and keeps what 

 it absorbs. 



t An account of the experiments with sulphur will form a chapter of 

 this monograph. 



