1879.] On Long-continued Stress on Elasticity of Metals, 221 



well-known decomposition of potassium iodide in sunlight has led us 

 to believe that in this case (KI) the phenomenon is of similar cha- 

 racter. The nature of this decomposition of potassium iodide has 

 been, much discussed, and observers, misled as it seems to us by a 

 supposed analogy with ordinary photographic reactions, have sin- 

 gularly failed to recognise the possibility of the oxidation of metallic 

 elements by light. Hence they have ascribed this behaviour of potas- 

 sium iodide to acids, carbonic and other, of the atmosphere. On this 

 point, however, we have satisfied ourselves ; first, that in a Sprengel 

 vacuum a 10 per cent, solution remains perfectly colourless in sun- 

 light ; and, secondly, that decomposition invariably occurs in an in- 

 solated solution when no other gases than nitrogen and oxygen are 

 present.* Here the oxidation can only be that of the alkali metal, 

 and analogy would suggest a similar inference in the case of the 

 oxalates. We are, however, still engaged on the investigation, and 

 our present object is rather to qualify the statement in our previous 

 paper as to the supposed indestructibility of an alkali-oxalate by sun- 

 light, than to advance to a conclusion for which the evidence is not 

 yet sufficient. 



XXI. "Preliminary Experiments on the Effects of Long- 

 continued Stress on the Elasticity of Metals." By J. TV 

 Bottomley, M.A., F.R.S.E. Communicated by Sir W. 

 Thomson, F.R.S. Received June 14, 1879. 



The following paper is intended to describe the results of experi- 

 ments on elasticity of wires which have been carried on during the 

 past two years, in the Natural Philosophy Laboratory in the Uni- 

 versity of Glasgow. 



In 1875, at the Glasgow meeting of the British Association, a 

 Committee was appointed, at the suggestion of Sir William Thomson, 

 for the purpose of commencing secular experiments on the elasticity 

 of wires, and a grant of money was placed at the disposal of the 

 Committee. 



These experiments have accordingly been commenced. An iron 

 tube about 70 feet long has been erected in the tower of the Uni- 

 versity. Two wires of gold, two of platinum, and two of palladium, 



* The mode in which we insured, as we believe, the absolute freedom of the air 

 employed from acid impurity was the following : — Exhausting tubes to a good 

 Sprengel vacuum, we admitted — by means of the apparatus we described in " Proc. 

 Roy. Soc," vol. xxviii, p. 210 — air which had been standing, with frequent 

 agitation, for six days over a solution of potassium hydrate. To make doubly sure, 

 the exhaustion was again repeated and the purified air a second time admitted. 

 The tubes thus treated acquired a brown tinge in light as quickly as did similar ones 

 simply plugged with cotton wool. 



