83 Dr. Matthiesseu on the Electric Conducting Power of 



having been previously boiled in small portions at a time with 

 metallic sodium to make it perfectly dry and free from oxygen. 

 Fig. 2 shows the process of pressing the wires. Here we have 

 the vice and the iron bars mentioned above, the latter connected 

 at the upper end in such a manner as to permit the pressure of 

 the vice to act on the steel press which is held between them at 

 the lower end within the trough of rock-oil ; the bar which is in 

 contact with the block of the press has an aperture through 

 which the wire can pass. As soon as the wire appears it is laid 

 hold of with pincers and inserted in a wire-holder, consi^ing of 

 two pieces of hard brass whose extremities are riveted at one end 

 to a thick copper wire, and press together at the other, as shown 

 in fig. 3 ; the copper wire is bent and fixed in the block of wood 

 i, fig. 2. The wire-holder was moved back and the wire increased 

 until it had attained the desired length, when it was cut off from 

 the press and fastened in the second wire-holder, the press and 

 bars being removed. In the trough a plate of glass was sup- 

 ported in such a position that the wire lay upon it, in order to 

 prevent the latter from distending through the effect of its own 

 weight : this precaution was especially necessary with potassium, 

 on account of the warmth of the weather in which the experi- 

 ments were made. To prevent as much as possible the absorp- 

 tion of the oxygen of the air by the rock-oil, a plate of glass was 

 placed over the trough as soon as the second end of the wire was 

 secured : fig. 4, representing a section of the trough, shows how 

 this plate was supported, allowing at the same time the free 

 movement of the wire-holders. 



As wires of calcium, strontium, and magnesium cannot be 

 obtained without the aid of heat, a glassblower's gas-lamp was 

 brought to bear on the press whilst under pressure between the 

 jaws of the vice ; a layer of asbestos placed between the pi-ess 

 and retaining bars prevented these from conducting the heat 

 away. With this arrangement I have even been able to press 

 tellurium, antimony, and bismuth wires, to whose conducting 

 powers I shall shortly return. 



The calcium and strontium wires were pressed into a tube 

 filled with rock-oil, which was held before the opening of the 

 press, so that the metal had only the distance of a few milli- 

 metres to pass through the air ; in the case of magnesium the 

 rock-oil was not necessary. As soon as the wires had attained 

 their desired length in the tubes, they were removed into the 

 trough of rock-oil mentioned above, where the wires were taken 

 out of the tubes, scraped at the ends, and fastened in the wire- 

 holders as before described. 



The method by which the electrical resistance was determined 

 was that given by Mr. Wheatstone, modified by the use of an 



