330 



NATURE 



[November 21, 191; 



tised in the arts, has had a surprisingh- small 

 share of the attention which has been paid to 

 metals by numerous observers in recent times. 

 Experiments made at the Mint - with coins and 

 coinagfe alloys gave such remarkable results that 

 tlie experiments were extended to pure metals, 

 and have enabled a fairly complete account of the 



Fig. I. — Structure of pure gola after being rolled. X ii. 



course of events in annealing to be clearly stated 

 for the first time. It appears, from a large 

 number of observations, that at comparatively low 

 temperatures metals and alloys, hardened by roll- 

 ing or hammering, are in an unstable condition, 

 and undergo a gradual change to the soft state. 

 The old standard silver and p'old trial plates, for 



example, have in the course of centuries, at the 

 ordinary temperature, become almost completely 

 softened, while lead appears to soften below the 

 ordinary temperature. As the temperature rises 

 the change is hastened, and a critical range Is 



" " 'I'he AnnealiiiR of Coin.-ige Alloys," Journal of the Institute of Metals. 

 September, i9t2. 



NO. 2247, VOL. go] 



passed through, \arying in extent for different 

 metals, below which annealing is too slow for prac- 

 tical purposes, while above it metals and alloys 

 revert from the hard to the soft stale almost in- 

 stantaneously. During the critical range, the time 

 required for annealing undergoes a significant re- 

 duction with each slight increment in the tempera- 

 ture, while above and below the critical range, the 

 change in the time is small even with great differ- 

 ences of temperature. 



Pari passu with softening, recrystallisation 

 takes place, not by diffusion, but by a change in 

 the orientation of molecules in situ, as predicted 

 by Dr. Beilby. When the softening is instan- 

 taneous, recrystallisation is almost, if not equally, 

 instantaneous. Thus, for example, pure gold, 

 which can be annealed in' a few davs in boiling 

 water, softens at once at 200°, and the large 

 primary distorted crystals (Fig. i) break up simul- 

 taneously into smaller irregular ones (Fig. 2). 

 The gradual growth of crystals, which has been 

 studied by Ewing and Rosenhain and by others, 

 takes place subsequently without much further 

 softening. T. K. Rose. 



INTERNATIONAL CONGRESS FOR 

 GENERAL AND MEDICAL RADIOLOGY. 

 "T^HE sixth meeting of the above congress was 

 -•- held this year at Prague, and was attended 

 by a large number of scientific workers. This 

 society has now a membership of 600, and em- 

 braces workers of many nationalities. The open- 

 ing meeting took place in the I^andes-Museum on 

 October 3, and was attended by more than 2000 

 people. At this meeting addresses were given by 

 Prof. Stoklasa, of Prague, who is president this 

 year, and by Prof. Becquerel, of Paris. At the 

 subsequent meetings of the congress, no fewer 

 than 130 papers were read on physical, biological, 

 and medical subjects. Among the excursions 

 made by the members was one to the uranium 

 mines of St. Joachimstal, from which most of the 

 radium in use has been obtained. 



The president chose for the subject of his 

 address the action of the rays from radioactive 

 bodies, and of ultraviolet light, on animal and 

 plant organisms. In the first part of his speech 

 he gave a short account of the development of our 

 knowledge of the connection between electricity 

 and life processes during the last two hundred 

 years. He gave next a summary of the results 

 of the last few years of the action of radium rays, 

 and of ultraviolet light, on living organisms. The 

 germination of seeds, and the development of 

 fungi, flowers, and leaves, may be accelerated 

 under certain conditions by these radiations, 

 whilst, under other conditions, these processes 

 may be entirely arrested. An intense source of 

 a-rays from radium, for instance, has a destructive 

 action on plant and animal organisms, while a 

 weak source has a stimulating effect. The action 

 of the more penetrating ;3-rays is similar to that 

 of the ultraviolet rays of short wave length. 

 These latter rays have a chemical action on the 



