476 Miscellaneous InteUlgence. 



zinc, and then place a crystal of nitre upon the latter in the fluid j a 

 dark band immediately forms around tiie crystals, sometimes ex- 

 tending over the whole surface of the mercury. All the nitrates, as 

 "well as nitricacid, actin this manner; butother salts, as the chlorate, 

 produce no effects of the kind j so that a very sensible test of the 

 presence of nitric acid is thus afforded. It is necessary that the 

 solution employed be a protosalt of iron. If nitric acid is sup- 

 posed to exist in a liquid, it should be saturated with potash, 

 evaporated to dryness, and the dry mass tried. Of course, salts of 

 copper or of silver must not be present. 



When an amalgam of brass is used instead of zinc, those effects 

 are not produced ; which M. Runge considers as a proof that the 

 zinc or brass is combined, chemically, with the copper. — Annalen 

 derPhysik, 1827, p. 479. 



6. On the decomposition of Ammonia by the Metals. — It has usually 

 been supposed, that when ammonia has been decomposed by the 

 metals, as iron, copper, &c., the latter did not increase in weight j 

 and although it had been remarked that tliey became brittle, it 

 "was considered as the result of some alteration in the arrangement 

 of their particles. M. Savart, engaged in researches on the elasticity 

 of bodies, had occasion to assure himself that there really was no 

 increase in the weight of the metals used, and although he acknow- 

 ledges that his experiments are as yet imperfect, still finds reason 

 to believe the ordinary opinion erroneous. 141.91 grs. of thin 

 copper wire were employed to decompose ammonia for four hours, 

 and then had become 142.382, having increased 0.472. As the 

 wire was slightly oxydized, the experiment was carefully repeated 

 with 28.86 grs. of copper wire, the ammoniacal gas being dried, 

 and every other precaution taken : the weight increased to 28.965, 

 so that the wire had increased g-^j of its weight, and had absorbed 

 0.105 of an unknown substance. The properties of the copper 

 had been altered in the usual manner, and the specific gravity of 

 the wire, which had been 8.8659, was now 7.7919. 



Iron produced exactly the same effects, except that the increase 

 in weight was less. A cylinder, weighing 40. 135, was used to de- 

 compose dry ammonia for nine hours, and then weighed 40. 195, 

 the increase being only 0. 06 or ^\q. This accords with some expe- 

 riments made by M. Thenard, The properties of the iron are much 

 changed by the operation, as has been observed ; it is more brittle 

 than before : but further, if left for an hour or two only in the 

 heated gas, its grain differs from that of ordinary iron, and resem- 

 bles that of steel ; it may then, also, be hardened and tempered, 

 and will strike fire with flint like ordinary steel. If the action has 

 continued for eight or ten hours, then the iron is not affected by 

 the hardening process ; it is softer than ordinary iron to the file, 

 has a grey black fracture, its grain partly resembling plumbago. 

 The specific gravity of the wire before the operation was 7.7883 

 after, 7.6637. 



