Properties of Pure Substances : Nitrogen. 33 



glycerine bath with the same precautions exactly as one uses 

 in taking a melting-point. I extract the following account 

 from my note-book verbatim: — " I could not detect any change 

 till about 230° C, at which temperature quiet decomposition 

 set in, and was complete and the tube clean at 235°. A con- 

 siderable portion of the thermometer stem was outside the 

 bath, though it did not begin to register till above 110°. 

 Making all allowances, the temperatures might on this account 

 have been anything less than 5° above those given. The tem- 

 perature rose very slowly, and the glycerine was kept well 

 stirred by a crescent-shaped stirrer of zinc. Experiments on 

 other bits of the tube were made by heating them in the bare 

 flame. In two of these (out of about four) there was a distinct 

 crepitation, but I did not note any flash, though that the 

 decomposition when once started ran very rapidly over the 

 whole mirror was well seen in all the experiments. The deposit 

 suddenly brightened with a puff of vapoar. I could detect no 

 nitrous smell. The temperature must hrve been 200 D 0. in all 

 cases. The platinum deposits were enormous, and the elec- 

 trodes torn up in all directions as described by Edison." 



These experiments may be considered to settle the question 

 of the cause of the effect observed by Professor Thomson and 

 myself in 1885 and 1886. No trace of the effect was ever 

 found unless the mercury was attacked ; and, contrariwise, the 

 mercury was never seen to be attacked without the " effect 3 * 

 making its appearance. It is curious to note the difference in 

 the readiness with which the action can be brought about, even 

 when all the circumstances of the experiments appear to be 

 identical. It is for this reason that I imagine that the reaction 

 requires the intervention of minute traces of some third sub- 

 stance, and the actual amount of these traces differs in different 

 experiments. When the reaction once commences it goes on 

 with increasing rapidity till near the end, and apparently 

 faster the more powerful the discharge. s One experiment 

 appears to indicate that even after the trimercuramine (?) is 

 decomposed its constituents are in a state of " labile " equi- 

 librium with respect to one another, and combine slightly or 

 separate according to some set of circumstances which I cannot 

 assign. It is curious, too, that the dissociation should be so 

 irreversible. Unless the mercury vapour continually liberated 

 is removed from the sphere of action — by combination with 

 the platinum deposit, for instance — I cannot understand the 

 effect of repeated heating ; and, indeed, I consider that the 

 suggestion just made is very possibly the true explanation. 



The condensation of nitrogen, therefore, at ordinary tem- 

 peratures has not been observed ; but it is possible that it may 



Phil Mag. S. 5. Vol. 35. No. 212. Jan. 1893. D 



