70 Mr. Hollo Appleyard on a 



It may be remarked here that, with the same apparatus, by 

 taking the mean of the two values of n, corresponding to 

 reversal of the battery, a second approximation could have 

 been made. Also the slide-wire is thinner than is required 

 by the temperature range. A thicker wire would have given 

 greater possibilities of accuracy, and it would have been less 

 liable to mechanical injury and temperature fluctuations. 



The Action of Sulphur Vapour upon Copper. 



While standardizing platinum thermometers in the vapour 

 of sulphur (444° C.) some mica plates, which formed part of 

 the apparatus within the vapour, were bound together with 

 copper wires which passed through holes in the mica. After 

 five hours' exposure to the vapour the apparatus was dis- 

 mantled, and, as had been expected, the copper wire was 

 completely demetailized. An examination of the resulting 

 wire, a brittle compound of cuprous or cupric sulphide, 

 showed that it was, in some cases, perforated by a small axial 

 hole; the wire had, in fact, become a tube of very small 

 bore. 



I am able to show this to you by projecting upon the 

 screen one of the pieces of mica through which the original 

 wire was threaded ; the ends of the sulphide wire were broken 

 off flush with each face of the mica, thus forming a section of 

 the sulphide wire. 



Prof. Ramsay tells me that, as a rule, it is possible to draw 

 an inner metallic core* from a copper wire which has been 

 treated with sulphur vapour. It therefore seemed probable 

 that my specimen was a piece of sulphide wire out of which 

 a core had fallen. This, however, does not appear to be 

 the explanation, for I have since succeeded in threading an 

 iron wire, of 8 mils diameter, completely through a sulphide 

 wire, which was more than half an inch long and not quite 

 straight. It is impossible that a core of 8 mils could have 

 fallen out of this specimen. 



An examination, with the microscope, of the original copper 

 wire does not reveal the slightest perforation ; although the 

 end was carefully removed with nitric acid so as to avoid the 

 closing of the hole, if one existed, by any mechanical cutting 

 of the wire. 



It was suggested that an occasional hole might occur in the 

 process of drawing the wire. Prof. Boys asked me to try a 

 piece of copper cut from a block. I therefore had a piece, of 

 square section, sawn from a large commutator-bar. After 



* I have obtained lately several specimens which show this core. 



