Properties of Pure Substances : Nitrogen. 27 



as to whether the ends of the limbs of the tube into which the 

 wires were fused were or were not at the same temperature 

 as the rest of the tube. However, there is no doubt that the 

 temperature of the ends was over 150° C, and yet when all 

 was cold again it was observed that the effect still amounted 

 to a difference of pressure of 3*4 millim. 



Now a compound of mercury and nitrogen, described as 

 trimercuramine, was obtained by Plantamour [Ann. Chem. 

 Pharm. xl. p. 115) by passing ammonia gas over mercuric 

 oxide. This substance is said to explode on heating, and 

 Plantamour gave it the formula Hg 3 N 2 on the strength of its 

 behaviour with copper oxide in a combustion-tube, though he 

 did not analyse it. The formula is, however, probably not 

 very far from being correct. Plantamour does not state the 

 temperature at which the nitride explodes, but says that if a 

 little heap of the substance be placed on a card or piece of 

 paper, and heated over the flame of a spirit-lamp, the explosion 

 will occur before the temperature is high enough for the paper 

 to be turned yellow. My compound certainly required a 

 higher temperature than this to start the explosion ; but it 

 is possible that its being in a nearly vacuous space, and very 

 much contaminated with free mercury, may have had some- 

 thing to do with this. Plantamour's compound exploded with 

 a white flame, which was bluish red at the edges ; the com- 

 pound I obtained emitted a brilliant bluish-white light on 

 explosion. There is some evidence from Plantamour's paper 

 that a temperature exceeding 200° C. prevents the formation 

 of the nitride from mercuric oxide and ammonia gas, and that 

 the best temperature at which to carry out the synthesis is 

 150° 0. These facts appear to point to the conclusion that 

 mercury nitride is a dissociable compound ; and the substance 

 I obtained is probably so, as the continuation of the history of 

 the tube will show. On June 22 the tube was wrapped in a 

 good deal of copper gauze, and the bundle so made and into 

 which three thermometers passed was placed in the air-bath. 

 The burners were regulated so as to give a stationary tempe- 

 rature, first of 185 c C. and then of 196° C. At the former 

 temperature the gauge appeared to show that some substance 

 was still undecomposed ; but there is some uncertainty, from 

 the ratio of the volume of the spark-tube to the gauge-tube not 

 being exactly known. Estimating these volume-ratios, how- 

 ever, as nearly as possible by means of external measurement, 

 and applying the necessary corrections, I found that the 

 pressure ought to be (as shown by the gauge) 5 millim. 

 greater on the tube side than on the sealed side. The ob- 

 served pressure-difference was 5'2 millim. — a better agreement 



