and on Dissociation, '. 451 



some of M. Troost and myself made at high temperatures. But 

 all experiments made up to this time, and especially the latest 

 researches of MM. Hofmann and Cahours, establish in the most 

 incontestable manner the closest analogy between nitrogen, 

 phosphorus, and arsenic, — but simply between these bodies in a 

 state of combination. It might, it is true, be objected that if a 

 certain number of difficultly volatile bodies, such as arsenic, 

 selenium, and tellurium, only represent one volume of vapour for 

 one equivalent, it depends on the high temperature of the 

 boiling-point. But mercury, according to M. Dumas, cadmium, 

 and especially zinc, which boils at 1040°, and whose density has 

 just been determined by MM. Troost and myself at 1100°, re* 

 present two volumes of vapour for one equivalent. This objec- 

 tion will disappear before examples which we wish to be able to 

 multiply. 



In short, the hypothesis according to which nitrogen enters 

 into combination in the state of a tempered body, like sulphur, 

 would explain the instability of these compounds, would remove 

 the majority of cases of inverse combination (that is, the decompo- 

 sitions accompanied by a disengagement of heat, which embarrass 

 the various theories of affinity), and it would, lastly, account for 

 the anomaly of removing nitrogen from phosphorus and arsenic, 

 its natural allies, which is at the present day a blot in our 

 systems of chemical analogies. 



I further think that the curious phenomena observed in 

 tempered sulphur, which my brother has minutely described, are 

 susceptible of a wide generalization. 



2. Dissociation. — The phsenomena of decomposition under the 

 influence of heat, of which nitrogen compounds furnish such an 

 excellent example, are not so evident when they take place at the 

 expense of bodies whose elements can unite during cooling, and 

 by simple contact. Mr. Grove's experiment, which I have had 

 occasion to repeat in conjunction with M. Debray*, by throwing 

 into water several kilogrammes of melted platinum and lighting 

 the explosive mixture which is abundantly disengaged, shows 

 clearly the products of the decomposition of water at this tem- 

 perature, but is far from telling what quantities of gas heat alone 

 could produce. In fact, the melted platinum is not in contact 

 with water, and can only decompose the small quantity of 



* On one occasion this experiment gave rise to a fearful explosion ; a 

 cast-iron mortar, weighing 16 to 20 pounds and full of water, was raised to 

 a considerable height ; 500 grammes of platinum were projected to a great 

 distance in a state of fine powder. The platinum usually traverses 30 to 40 

 centimetres of water, sinks in a fused or soft state to the bottom, and forms 

 a regulus with a mammillary surface ; the transparency of the water is dis- 

 turbed by thousands of small gas bubbles, which can be exploded at the 

 surface. . 



