of Pure Metals Sfc. at the Boiling-point of Oxygen. 327 



non-metals at the low temperatures obtainable by the evapora- 

 tion of liquid oxygen at ordinary barometric pressures and the 

 ebullition of liquid oxygen under reduced pressures of about 

 25 or 30 millim. Since liquid oxygen, as already pointed out 

 by one of us, is a very perfect insulating fluid, it is quite a 

 simple matter, if once sufficient of the liquid gas is ob- 

 tained, to measure the electrical resistance of a wire or small 

 rod of the metal when immersed in liquid oxygen, and 

 thus entirely at the same temperature as the evaporating 

 liquid. A series of observations has accordingly been made 

 by us on the specific electrical resistances of various metals, 

 non-metals, and alloys over a range of temperature varying 

 from +100° C. to nearly -200° C, and although these in- 

 vestigations are as .yet incomplete, the observations already 

 made seem to be of sufficient interest to render it worth while 

 to place them on record. 



§ 2. A number of small resistance-coils were prepared of 

 wires of different metals and alloys in the following way. A 

 thin rectangular sheet of mica, about 5 centim. long and 1 or 

 2 centim. in width, had a number of nicks cut in the edges, 

 and round this was wound loosely the wire whose resistance 

 was to be determined. The ends of the wire were brought 

 out through two holes in the mica and soldered to two stout 

 copper terminal wires formed of high-conductivity copper 

 wire well insulated with indiarubber. The ends of these 

 terminal wires were bent over so as to dip into mercury cups 

 (see fig. 1). The small resistance-coil so formed could then 

 be lowered into a test-tube full of the liquid gas or other fluid, 

 by means of which the temperature of the wire was deter- 

 mined. The majority of the wires used had a length of 50 

 or 100 centim. and a diameter of *003 of an inch (3 mils). 

 The electrical resistance of these small coils of wire was 

 measured by a Wheatstone's bridge, kindly lent for the 

 purpose by Messrs. Elliott Bros. The coils of this bridge were 

 of platinum-silver, and adjusted to read in B.A. units at 15°\o 

 Cent. The balance was determined by the use of a highly 

 sensitive mirror- galvanometer, using the current from a single 

 Helsen's dry cell. The experiments were carried out in the 

 Royal Institution laboratories, in a room which remained 

 approximately at about 2o° (J. during the whole time. A 

 series of wires of pure metals was obtained, and also others of 

 known alloys. Mr. J. S. Sellon and Mr. Gr. Matthey, of 

 Messrs. Johnson and Matthey of Hatton Garden, kindly 

 provided for us carefully drawn wires of absolutely pure 

 annealed platinum, pure gold (999*9 degrees of fineness), 

 pure silver, aluminium, and tin. Also wires of alloys of 



2 A2 



