CHEMISTRY. (CHEMICAL PHYSICS.) 



103 



point. Hydrogen therefore follows the law of 

 Dulong and Petit, and has the greatest specific 

 heat of any known substance. The surface ten- 

 sion of hydrogen at its boiling-point was about 

 one-fifth that of liquid air under similar condi- 

 tions. It did not exceed one-thirty-fifth of the 

 surface tension of water at ordinary temperatures. 



Free hydrogen, helium, and neon have been 

 separated from the air by two methods, one of 

 which depends on the use of liquid hydrogen to 

 boil the dissolved gases out of air kept at the 

 boiling-point of nitrogen, and the other on a sim- 

 ple arrangement for keeping the more volatile 

 gases from getting into solution after partial ex- 

 haustion. A gaseous material was found in the 

 air that could be separated without the liquefac- 

 tion of the air. The spectroscopic examination 

 of this matter was reserved to be dealt with in 

 a separate paper by Prof. Liveing and the author. 



Helium from the gas at the King's Well, Bath, 

 was subjected by Prof. Dewar to a pressure of 80 

 atmospheres with part of the narrow portion of 

 the glass tube in liquid hydrogen. On sudden 

 expansion, a mist from the production of some 

 solid body was clearly visible. It proved, how- 

 ever, to be caused by some other material than 

 helium, probably by neon. A similar mist was 

 seen with hydrogen under similar conditions of 

 expansion and certain relations (specified by the 

 author) to its critical temperature; and from this 

 experience applied to interpret the helium experi- 

 ments, the critical temperature of helium gas \vas 

 computed to be under 9 absolute. It is now 

 safe to f say, Prof. Dewar continues, that helium 

 has been really cooled to 9 or 10 absolute 

 without any appearance of liquefaction. On ac- 

 count of the small refractivity of helium the 

 liquid must be far more difficult to see than 

 liquid hydrogen. The hope of being able to liquefy 

 helium, which would appear to have a boiling- 

 point of about 5 absolute, or one-fourth that of 

 liquid hydrogen, is dependent on subjecting 

 helium to the same process that succeeds with 

 hydrogen, only instead of using liquid air under 

 exhaustion as the primary cooling agent, liquid 

 hydrogen under expansion must be employed, and 

 the resulting liquid collected in vessels surrounded 

 with liquid hydrogen. From a tabular statement 

 of the results of theory and experiment given by 

 the author, it appears that by the employment 

 of liquid or solid hydrogen as a cooling agent, 

 we ought to be able to liquefy a body having a 

 critical point of about 6 or 8 absolute, and a 

 boiling-point of about 4 or 5 absolute. Even 

 then, if liquid helium could be produced with the 

 probable boiling-point of 5 absolute, this sub- 

 stance would not enable us to reach the zero of 

 temperature; another gas must be found that is as 

 much more volatile than helium as helium is than 

 hydrogen in order to reach within 1 of the zero 

 of temperature. 



Among miscellaneous observations made by the 

 author in the course of his inquiry is that of the 

 great increase of phosphorescence in the case of 

 organic bodies cooled down to the boiling-point 

 of hydrogen, which is very marked when com- 

 pared with the same effects brought about by the 

 use of liquid air. Photographic action is still 

 lively, although it is reduced to about half the 

 intensity it bears in liquid air. Some crystals 

 placed in liquid hydrogen became for a time self- 

 luminous on account of the high electric stimula- 

 tion brought about by the cooling, causing actual 

 electrical discharges between the crystal mole- 

 cules. 



Prof. Dewar, in his lecture on Gases at the 

 Beginning and the End of the Nineteenth Cen- 



tury, said that while he had at orio time thought 

 he had liquefied helium, he had found that he had 

 not. The gas he had then dealt with had proved 

 to be a mixture of helium with some other gas 

 or gases -that can be liquefied, but pure helium 

 had not yet been obtained in liquid form. When 

 it becomes possible to prepare liquid helium in 

 any quantity, we may hope to get down to tem- 

 peratures lower than any obtained with hydrogen, 

 and approaching closely to the absolute zero. 



In the course of the dynamic investigation of 

 the bromination of aromatic compounds, the de- 

 pendence of the velocity of bromination on the 

 nature and position of the substituting groups 

 of the benzene ring has been studied by L. Brun- 

 ner, and especially the catalytic activity of the 

 most important brornin " carriers." In respect 

 to this capacity, aluminum, chromium, iron, and 

 thallium salts, compounds of antimony and phos- 

 phorus, and iodin have been examined. The 

 catalytic activity of the bromin " carriers " was 

 found to depend upon the nature of the substance 

 which was being disseminated., so that the ar- 

 rangement of these bodies in a general series ac- 

 cording to their activity is now possible. For 

 benzene and bromobenzene the order is aluminum, 

 iron salts, iodin, antimony, phosphorus, halogens. 



The investigations of radioactive substances 

 and the properties of radioactivity continue to 

 yield novel and interesting results. M. and Mine. 

 Curie have established the fact that when any 

 substance is placed near a radiferous salt of 

 barium it becomes itself radioactive. The radio- 

 activity persists long after removal of the barium 

 salt, but decreases with time, at first rapidly, and 

 then more and more slowly. A. Debierne observed 

 similar phenomena when salts of barium were 

 placed in intimate contact with salts of his acti- 

 nium. MM. Curie and Debierne, subjecting ra- 

 dium to air exhaustion in a glass vessel, found 

 that the vacuum steadily decreased through the 

 giving out of a gaseous substance which, when 

 collected, was found to be intensely radioactive. 

 Mme. Curie observed irregularities in the' radio- 

 activity of oxid of thorium that have not yet 

 been explained, but for a part of which Owens 

 suggests that air currents might account. E. 

 Rutherford, of McGill University, observed that 

 air which had been kept near oxid of thorium, 

 and was then taken some distance away, retained 

 its conducting power for several minutes, and 

 finding similar powers possessed by other thorium 

 compounds, concluded that a particular radio- 

 active emanation susceptible of being carried off 

 by the air was given off by them. M. Dorn repro- 

 duced the experiments of Owens and Rutherford 

 with radiferous salts of barium. Rutherford found 

 that the emanation given off from a specimen of 

 radium was small at atmospheric temperature, 

 but could be enormously increased by slightly 

 heating the radium, so that he obtained in this 

 way 10,000 times the amount of emanation given 

 off at ordinary temperatures. Imprisoned in a 

 closed vessel, the emanation remained radioactive 

 a long time. The results of further experiments 

 pointed to the conclusion that the emanation 

 from radium was a radioactive gas, with a molec- 

 ular weight probably lying between 40 and 100. 

 Experimenting on the communication of radio- 

 active properties to distilled \vater, M. and Mme. 

 Curie and M. A. Debierne have observed that 

 under certain conditions water can be made even 

 more active than the body from which the influ- 

 ence is communicated. When kept in a sealed 

 tube the water loses the greater part of its activ- 

 ity in a few days. When- in an open vessel the 

 loss of activity is much more rapid, and is more 



