262 HEAT OF FORMATION OF NITROGEN SULPHIDE. 



electric current. Two experiments gave, the volume being 

 constant 



Weight of the Heat given off Per equivalent 



substance. per grm. (46 grms.). 



2-997 grms 701-1 



2-979 700-4 



Mean 700-7 



At a constant pressure, we should have had + 31 '9. The 

 experiment gave for 1 grm. 243*1 cms. of gas (the volume being 

 reduced to and 76 metre). 1 



Theory gives 242*2 cub. cms. 



These gases consisted of pure nitrogen, within about 25o^ n - 

 Thus the decomposition was produced according to the equation 

 NS = N -|- S, i.e. the nitrogen sulphide is resolved purely and 

 simply into its elements. 



4. Heat of formation. From these results we conclude that 

 the formation of nitrogen sulphide from its elements, 



N + S = NS, absorbs - 32*2 Cal, 



the volume being constant, or 31*9 Cal. at a constant pressure. 



This formation is, therefore, endothermal, which explains why 

 it does not take place directly. But it is effected by making 

 ammoniacal gas act upon sulphur chloride. The chlorine in 

 this latter compound unites with the hydrogen of the ammonia 

 to form hydrochloric acid, and consequently ammonium chloride, 

 while the nitrogen sulphide is forming. This transformation 

 finally gives off 4- 123*0 Cal. The energy consumed in the 

 association of the sulphur and the nitrogen (31*9) is thus 

 furnished by the formation of the hydrochloric acid, or rather 

 by that of the ammonium chloride, at the expense of the sulphur 

 chloride and the ammoniacal gas (+ 230*1 75*2). 



5. It will be observed that the combination of the nitrogen 

 with the sulphur absorbs heat ( 31*1 Cal.), exactly like the 

 combination of nitrogen with oxygen ( 21*6 Cal.). The 

 nitrogen sulphide is, therefore, analogous to nitric oxide as 

 regards its endothermal character, as well as its formula. This 

 is a fresh proof of the general analogy existing between the 

 conditions of formation of oxygenated compounds and those of 

 sulphuretted compounds. It is difficult to carry further these 

 points of resemblance in the heats of formation, seeing that the 

 conditions of the two compounds are not comparable, any more 

 than the conditions of the elements, although a certain com- 

 pensation may be allowed between the solid form of the sulphur 

 and that of nitrogen sulphide. 



6. Heat of combustion. If we are working in air or in oxygen, 

 nitrogen sulphide burns 



NS + 2 = N + S0 2 , 

 and gives off -f 101*1 at a constant pressure. 



