CHEMISTRY. (CHEMICAL PHYSICS.) 



109 



trated condition has been investigated in Van't 

 I luff's laboratory by Dr. Ewan, who selected for 

 study the course of the slow oxidation of sul- 

 phur and of phosphorus. With phosphorus and 

 oxygen (saturated with aqueous vapor at 20) it 

 was observed that for pressures of oxygen greater 

 than 700 millimetres the velocity of oxidation is 

 excessively small, or nothing at all. Below 700 

 millimetres it increases very rapidly. This 

 limit corresponds to that found by Joubert, 

 below which phosphorescence begins. After 

 reaching its maximum velocity a very simple 

 relation exists between the rate of oxidation 

 and the pressure of the oxygen, provided that 

 the change in the rate of evaporation of the 

 _phosphorus which, according to Stefan, is pro- 

 duced by the change in pressure is taken into 

 account. The rate of oxidation is then di- 

 rectly proportional to the pressure of oxygen. 

 In absence of water the oxidation also begins 

 suddenly, but at a lower pressure (about 200 mil- 

 limetres). Taking into account the change in 

 the rate of evaporation, the velocity of oxidation 

 then reaches a maximum at a pressure which is 

 approximately the same as that which Van't 

 Hoff formerly found to be the most favorable 

 for the explosive combustion of phosphine. Af- 

 ter the maximum the relation between the ve- 

 locity of the reaction and the pressure could not 

 be made out with certainty, because in dry oxy- 

 gen the coating of oxide which forms on the 

 surface disturbs the regular course of the reac- 

 tion. With sulphur and dry oxygen, where the 

 slow oxidation can be conveniently followed at 

 160, this relation has, however, been obtained. 

 It appears, again, taking into account the change 

 in the velocity of evaporation, that the velocity 

 of the oxidation is proportional to the square 

 root of the pressure. This would appear to point 

 to the conclusion that in the absence of water 

 the active part of the oxygen is only that very 

 small part of it which is broken up into atoms. 

 This conclusion is perhaps supported in the case 

 of phosphorus by the combustion of one of the 

 products of oxidation in dry oxygen viz., P 4 0. 

 A communication was made to the British As- 

 sociation by Lord Rayleigh and Prof. William 

 Ramsay concerning the existence of a hitherto 

 undiscovered gas in the atmosphere. Certain 

 experiments of Cavendish, it appears, pointed to 

 the presence in the air of some substance other 

 than the gases with which we are familiar. At- 

 tention was recalled to the subject by the fact 

 that the density of nitrogen obtained from at- 

 mospheric air differs by about -A- per cent, from 

 the density of nitrogen obtained from other 

 sources. It was found that if air (with excess 

 of oxygen) be subjected to electric sparks, the 

 resulting nitrous fumes absorbed by potash and 

 the excess of oxygen by alkaline pyrogallate, a 

 residue remains which is neither oxygen nor 

 nitrogen, as can be seen from its spectrum. The 

 same gas can be isolated by exposing nitrogen 

 obtained from air to the action of magnesium. 

 As the magnesium gradually absorbs the nitro- 

 gen, the density of the residual gas rises to near- 

 ly 20. The alleged new substance constitutes 

 nearly 1 per cent, of the atmosphere, and gives 

 a spectrum with a single blue line much more 

 intense than the corresponding blue line in the 

 nitrogen spectrum. Prof. Dewar has since sug- 



gested that the supposed new gas may be an al- 

 lotropic form of nitrogen. 



In his address before the chemical section of 

 the British Association (1893) Prof. J. E. Rey- 

 nolds mentioned as the most remarkable out- 

 come of "comparative chemistry " the periodic 

 law of the elements, which asserts that the prop- 

 erties of the elements are connected in the form 

 of a periodic function with the masses of their 

 atoms. Concurrently with the recognition of 

 this principle other investigations have been in 

 progress, aiming at more exact definitions of the 

 characters of the relations of the elements, and 

 ultimately of their respective offices in nature. 

 Among inquiries of this kind the comparative 

 study of the elements carbon and silicon appears 

 to possess the highest interest. Carbon, whether 

 combined with hydrogen, oxygen, or nitrogen, 

 or with all three, is the great element of organic 

 nature ; while silicon, in union with oxygen and 

 various metals, not only forms about one third of 

 the solid crust of the earth, but is unquestion- 

 ably the most important element of inorganic 

 nature. The chief functions of carbon are those 

 which are performed at comparatively low tem- 

 peratures; hence carbon is essentially the ele- 

 ment of the present epoch. On the other hand, 

 the activities of silicon are most marked at very 

 high temperatures ; hence it is the element whose 

 chief work in nature was performed in the dis- 

 tant past, when the temperature of this earth 

 was far beyond that at which the carbon com- 

 pounds of organic life could exist. Yet between 

 these dominant elements of widely different 

 epochs remarkably close analogies are traceable, 

 and the characteristic differences observed in 

 their relations with other elements are just those 

 which enable each to play its part effectively 

 under the conditions which promote its greatest 

 activity. 



The phenomena of fluorescence, of phospho- 

 rescence in air on exposure to light, and of phos- 

 phorescence of substances in a vacuum under 

 the influence of the electric discharge, are re- 

 garded by H. Jackson as of the same order, and 

 to consist in a response on the part of the sub- 

 stances to the operation of radiant energy prop- 

 agated after the manner of light in undulations 

 of short length. 



The nature of the molecule of calomel has been 

 in dispute. The determinations of the vapor den- 

 sity of mercurous chloride made by Mitscherlich. 

 Deville and Tront. and Rieth afforded numbers 

 in close agreement with those demanded by the 

 simple formula HgCl. Odling, however,* dis- 

 puted the possibility of the existence of mole- 

 cules containing only one atom of each element, 

 involving the assumption of univalency for mer- 

 cury, and showed that when gold leaf is im- 

 mersed in the vapor it becomes amalgamated, 

 indicating the presence of free mercuric vapor. 

 The debate has continued. Recent experiments 

 by Prof. Victor Meyer and Mr. Harris have led 

 them to the conclusion that when calomel is 

 vaporized it dissociates into mercury and cor- 

 rosive sublimate Hg 2 C] 2 =Hg + HgC] 2 , and that 

 the necessity for the assumption of monadic val- 

 ency for mercury is thus avoided. 



Chemical Physics. Notwithstanding the 

 large amount of evidence now placed on record 

 that substances commonly supposed to be ca- 



