and Sodium with Platinum and Mercury. 



161 



instrument manufactured by Leeds and Northrup, of most 

 excellent performance. It was used, of course, with telescope 

 and scale. 



The form of the thermo-couples finally arrived at after 

 many trials and rejections was as shown in the accompanying 

 diagram. For clearness, the branch EF is represented in the 

 plane of the paper ; it was actually bent in a plane at right 

 angles thereto, as toward the reader. 



This apparatus was constructed of ordinary glass tubing of 

 about 0'4 cm diameter, with platinum wires fused in at A and 



B. The distance between A and B is about 55 cm and the 

 vertical distance AC or BD about 10 cm . The branch EF is 

 about 15 cm long. The platinum wires were of number 32 

 B & S gauge, and each was about 100 cm in length. Three 

 such pieces of apparatus were built, as nearly as possible, alike ; 

 the six pieces of platinum wire required were cut from a single 

 piece of about 600 cm length supplied by Eimer & Amend. 



The tubes were filled respectively with potassium, sodium 

 and mercury, these metals being drawn in at the end F by 

 suction applied by the mouth to a rubber tube connected at Gr. 

 Mercury, of course, was simply drawn in at the ordinary room 

 temperature. To introduce the other two metals, the tubes 

 were heated, filled with melted paraffin and again emptied, and 

 then filled with the metal, previously melted under paraffin in 

 a test tube. In drawing in the alkali metals, the mouth was 

 protected against accident by a glass trap interposed in the 

 rubber tube between the mouth and the opening G. The par- 

 affin used was ordinary white paraffin of commerce melting at 

 about 45° to 50°. 



It was found that the potassium and sodium in lumps of sev- 



