presf:nt problems of tnorgatstic chemistry. 211 



a consideration of oxygen compounds. JNIoissan's hi-illiaid work on 

 fluorides, liowever, has shown that SF,, is capable <»f stahle existence, 

 and this forms a stroiifr arirument in sup})ort of the hexad character 

 of sulphur. The tetravakMicv of oxygen, un(U'r hehtting conditions, 

 too, is being acknowledged, and this may he reconciled with the 

 existence of water of crvstalli/ation. as well as of the per-salts already 

 mentioned. The adherence of annnonia to many chlorides, nitrates, 

 etc., points to the connecting link being ascril)able to the pentavalency 

 of nitrogen; and it might l)e worth while investigating similar com- 

 j)0unds with phosphoretted and arsenicorretted hydrogen, especially 

 at low temperatures. 



The progress of chemical discovery, indeed, is closely connected 

 with the invention of new methods of research, or the submitting of 

 matter to new^ conditions. While Moissan led the way by elaboi-ating 

 the electric furnace, and thus obtained a potent agent in temperatures 

 formerly unattainable. Spring has tried the effect of enormous pres- 

 sure, and has recently found chemical action between cui)rous oxide 

 and sulphur at ordinary temperature, provided the [)ressure be raised 

 to 8,000 atmospheres. Increase of ])ressure appears to lower the tem- 

 perature of reaction. It has been known for long that explosions will 

 not propagate in rarefied gases, and that they became more violent 

 when the reacting gases are compressed; but we are met with difficul- 

 ties, such as the noncombination of hydrogen and nitrogen, even at 

 high temperature and great pressure; yet it is possible to measure the 

 electromotive force (0.59 volt) in a couple consisting of gaseous nitro- 

 gen and gaseous hydrogen, the electrolyte being a solution of aunno- 

 nium nitrate saturated w^ith ammonia. Chemical action betw^een dis- 

 solved hydrogen and nitrogen undoubtedly occurs; but it is not con- 

 tinuous. Again we may ask. Why? The heat evolution should be 

 great; the gain of entropy should also be high werc> direct combina- 

 tion to occur. Why does it not occur to any measurable extent? Is 

 it because for the initial stages of any chemical reaction the reacting 

 molecules must be already dissociated and those of nitrogen are not? 

 Is that in any way connected with the abnormally low density of 

 gaseous nitrogen? Or is it that, in order that combination shall 

 occur, the atoms nuist fit each other; and that in order that nitrogen 

 and hydrogen atoms may fit they must be greatly distorted? But 

 these are speculative questions, and it is not obvious how experiments 

 can be devised to answ^er them. 



Many compounds are stable at low temperatures Avhich dissociate 

 when temperature is raised. Experiments are being made, now that 

 liquid air is to be purchased or cheaply made, on the combinations of 

 substances which are indifferent to each, other at ordinary tempera- 

 tures. Yet the research must be a restricted one, for most substances 

 are solid at — 185°, and refuse to act on each other. It is probable. 



