October 12, 1905] 



NATURE 



599 



a short time, and is still under investigation. Like the 

 blue tint, the radio-activity persists after drastic treatment. 

 To me this proves that radio-activity does not merely 

 consist in the adhesion of electrons or emanations given off 

 by radium, to the surface of an adjacent body, but the 

 property is one involving layers below the surface, and like 

 the alteration of tint is probably closely connected with 

 the intense molecular excitement the stone had e.xperienced 

 during its twelve months' burial in radium bromide. 



.\ diamond that had been coloured blue by radium, and 

 had acquired strong radio-active properties, was slowly 

 heated to dull redness in a dark room. Just before visibility 

 a faint phosphorescence spread over the stone. On cooling 

 and examining the diamond, it was found that neither the 

 colour nor the radio-activity had suffered appreciably. 



The diamond is remarkable in another respect. It is 

 extremely transparent to the Rdntgen rays, whereas highly 

 refracting glass, used in imitation diamonds, is almost 

 perfectly opaque to the rays. 1 exposed for a few seconds 

 over a photographic plate to the X-rays the large Delhi 

 diamond of a rose-pink colour weighing 312 carats, a 

 black diamond weighing 23 carats, and a glass imitation 

 of the pink diamond. On development, the impression 

 where the diamond obscured the ravs was found to be 

 strong, showing that most rays passed through, while the 

 glass was practically opaque. By this means imitation 

 diamonds can readily be distinguished from true gems. 



1 have already signified that there are various degrees 

 of refractoriness to chemical reagents among the different 

 forms of graphite. Some dissolve in strong nitric acid ; 

 other forms of graphite require a mixture of highly con- 

 centrated nitric acid and potassium chlorate to attack 

 them, and even with this intensely powerful agent some 

 graphites resist longer than others. M. Moissan has shown 

 that the power of resistance to nitric acid and potassium 

 chlorate is in proportion to the temperature at which the 

 graphite was formed, and with tolerable certainty we can 

 estimate this temperature by the resistance of the specimen 

 of graphite to this reagent. 



The superficial dark coating on a diamond after exposure 

 to molecular bombardment I have proved to be graphite.' 

 M. Moissan - has shown that this graphite, on account of 

 its great resistance to oxidising reagents, cannot have been 

 formed at a lower temperature than 3600° C. 



It is thus manifest that the bombarding electrons 

 endowed with an electric charge, and striking the diamond 

 with enormous velocity, raise the superficial layer to the 

 temperature of the electric arc, and turn it into graphite, 

 whilst the mass of diamond and its conductivity to heat are 

 sufficient to keep down the general temperature to such a 

 point that the tube appears scarcely more than warm to 

 the touch. 



A similar action occurs with silver, the superficial layers 

 of which can be raised to a red heat without the whole 

 mass becoming more than warm.' 



I will now direct your attention to a strange property 

 of the diamond, which at first sight might seem to discount 

 the great permanence and unalterability of this stone. It 

 has been ascertained that the cause of phosphorescence is 

 in some way connected with the hammering of the 

 electrons, violently driven from the negative pole, on to 

 the surface of the body under examination, and so great 

 is the energy of the bombardment that impinging on a 

 piece of platinum or even iridium the metal will actually 

 melt. When the diamond is thus bombarded in a radiant 

 matter tube the result is startling. It not only phos- 

 phoresces, but assumes a brown colour, and when the 

 action is long-continued becomes almost black. 



I will project a diamond on the screen and bombard it 

 with radiant matter before your eyes. I do not like to 

 anticipate a failure, but I am at the mercy of my diamond. 

 I cannot rehearse this experiment, and it may happen that 

 the diamond I have selected will show caprice and not 

 blacken in reasonable time. Some diamonds visibly 

 darken in a few minutes, while others, more leisurely in 

 their ways, require an hour. 



This blackening is only superficial, but no ordinary 

 means of cleaning will remove the discoloration. Ordinary 



1 Chemicnl News, vol. Ixxiv., p. 39, July, 1896. 



- Comptcs rendiLs, c.\xiv., p. 653. 



■' Proc. Roy. Soc, vol. I., p. 99, June, 1891. 



oxidising reagents have little or no effect in restoring the 

 colour. The black stain on the diamond is due to a form 

 of graphite which is resistant to oxidation. 



Conversion of Diamond irtto Graphite. 

 .\lthough we cannot convert graphite into diamond, we 

 can change the diamond into graphite. I take a clear 

 crystal of diamond and place it between two carbon poles, 

 and throw the image on the screen by means of a powerful 

 arc lamp behind. I now bring the poles with intervening 

 diamond together and form an arc between. The tempera- 

 ture of the diamond rapidly rises, and when it approaches 

 3600° C, the vaporising point of carbon, it breaks down, 

 swells, and changes into black and valueless graphite. I 

 show this experiment because it is striking and suggestive. 

 I may add that it is costly — because the stone, if not of 

 fine quality, might easily burst. 



NO. 1876, VOL. 72] 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Sir Clements R. Makkii.a.m, K.C.B., F.R.S., will deliver 

 an address at Cambridge on Thursday, October 19, intro- 

 ductory to the courses of instruction in geography. 



.ScjY'nce announces the death of General Isaac J. Wistar, 

 of Philadelphia, founder of the Wistar Institute of Anatomy 

 and Biology of the University of Pennsylvania, formerly 

 president of the American Philosophical Society. By his 

 will the Wistar Institute will receive the residue of his 

 estate, thought to amount to about 80,000/. 



In the course of an address to the students of Cornell 

 University in 1903, President Schurman emphasised the 

 necessity of a systematic distribution of the daily time 

 of college students. He recommended the following general 

 apportionment of hours : — for work, eleven ; for sleep, 

 eight ; for amusement, one ; for meals and athletics, two 

 hours each. Work is made to include not only time spent 

 in the laboratory and lecture-room and in private study, 

 but also time given to societies and to self-support. This 

 advice led Dr. Guy M. Whipple, of Cornell University, to 

 try to ascertain how the students in his university actually 

 do distribute their daily time. The results of his inquiries 

 are described in an article in the current number of the 

 Popular Science Monthly. In the summary to the detailed 

 tables given in his article Dr. Whipple states that, taking 

 the university as a whole, the average Cornell student 

 devotes just nine hours daily to college work, sleeps 

 79 hours, devotes 2-23 hours to amusement, 172 hours 

 to physical exercise, 1-4 hours to meals, 039 hour to self- 

 support, and 1-36 hours to unclassified activities. The 

 average length of time given to work is greatest in the 

 college of medicine, and progressively less in those of 

 engineering, law, agriculture, and arts. Both in the 

 university at large and within the College of Arts and 

 Sciences, men give more time to college work than women. 



Prof. J. W. Judd, F.R.S., distributed on October 5 the 

 medals and prizes gained during the past session by the 

 students of the Royal College of Science, London, in the 

 lecture theatre of the Victoria and .Albert Museum, South 

 Kensington. The Dean, Prof. Tilden, F.R.S., in opening 

 the proceedings, referred with regret to several losses 

 which the college and school had sustained during the 

 year, alluding particularly to the death of Prof. Howes. 

 The geological division had lost its chief by the retire- 

 ment of Prof. Judd. The college is now, the Dean con- 

 tinued, in an attitude of expectancy in regard to the 

 future, and it is possible that next year they will be able 

 to hold the prize distribution in the new buildings. He 

 said that in ten years seventy-six of the students of the 

 college have taken the degree of B.Sc, and, in addition, 

 thirty have taken first-class honours, besides which there 

 are nine doctors of science. Prof. Judd, having distributed 

 the awards, addressed the students. He acknowledged the 

 uniform courtesy and consideration which he had received 

 from colleagues and students alike during his forty-five 

 years' experience in connection with the school. Nearly 

 two-thirds of that period had been spent in the position of 

 one of the teachers. He congratulated them on the ex- 

 pansion and development which is now promised, and 

 expressed the hope that the change would lead to even 



