20 DR. F. HORTON ON THE EFFECTS OF CHANGES OF TEMPP:RATURE 



PAKT IL 

 ACCOUNT OF THE EXPERIMENTS. 



The wires experimented on were, except in a few cases, chemically pure, and were 

 supplied by Messrs. JOHNSON, MATTHEY & Co., of Hatton Garden, London. They 

 were all of approximately the same length and diameter. In order to get them into 

 comparable conditions, they were carefully annealed before the rigidity determinations 

 were begun. This was done by repeatedly heating with an electric current, the 

 oxidisable wires, iron and steel, being enclosed in an atmosphere of pure dry 

 hydrogen, copper in carbonic acid gas, and the others in air. In each case about a 

 metre of the wire was suspended vertically in a glass tube, a light weight being 

 attached to its lower end. This closed an electric circuit by dipping into some 

 mercury at the bottom of the tube. In the cases of steel and of iron the tube was 

 then repeatedly exhausted and filled with pure dry hydrogen until all the air had 

 been removed. Carbonic acid gas was used instead of hydrogen in the case of 

 copper ; gold, silver, platinum and aluminium were heated in air. The wire was 

 then repeatedly heated to a red heat by means of an electric current, each heating 

 lasting for several minutes. The temperature attained was of course highest in the 

 case of those metals which are furthest from their melting points at ordinary 

 temperatures. Platinum was taken almost to white heat, and iron and steel well 

 above the temperature of recalescence. After this treatment, a length of about 

 60 centims. was cut from the middle of the annealed wire and suspended in the 

 heating jacket. All the specimens used were quite straight and free from kinks, 

 and special care was taken to see that the wire had not been heated to too high a 

 temperature, or subjected to any permanent elongation by the tension to which it 

 was subjected during the annealing. The wires were all bright and free from oxide. 



The softer metals, lead, tin, and cadmium, were annealed by suspending them 

 (without any weight attached to their lower ends) in a vertical combustion tube, 

 heated by means of vertical rows of small Bunsen burners. A thermometer was 

 suspended beside the wire, and the temperature was not allowed to exceed two-thirds of 

 the melting point of the metal in question. The temperature was kept up for about 

 an hour, and then the tube was allowed to cool down very gradually. The heating 

 and cooling were repeated many times. Some unaunealed wires Avere also 

 experimented on. 



Before giving the results in detail for the different wires, it would be well to 

 mention that in every case examined, with the exceptions of pure copper and steel, 

 it was found that the modulus of rigidity at a constant temperature was not 

 constant, but increased as time went on. This increase was generally very small, 

 and was greater at the higher temperatures than at the ordinary temperature of the 



