1SI.Sc. (Vict.). ALTHOUGH the chemistry of the nitrides is of considerable interest from many points of view, little is definitely known concerning these compounds. Since the discovery of azoimide, which reacts with metals to form a class of nitrides, i t became of interest to compare the properties of the latter with nitrogen compounds of the metals obtained by other means. Iron nitride, from its fairly easy decomposability, appeared likely to present some interesting reactions and possibly t

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... allow of a determination of its heat of formation. The earliest work on the combination of iron and nitrogen was done by Berthollet, and by Thenard (2'~aitd de Chimie, 1834, i, 434), who allowed ammonia to act on iron wire a t a red heat and found that the weight of tho iron scarcely increased, but that the metal became brittle. Savart (quoted by Stahlschmidt, Pogg. Ann., 1865, 125, 37) mentioned that after ammonia had passed over iron for a long time the metal became softer, whilst'after an action of only two hours it behaved like steel and could be hardened. These observers did not recognise the formation of iron nitride. According to Desprets (Ann. Chim. Phys., 1829, 42, 122), iron increased in weight from 7 t o 111.5 per cent. by heating in ammonia and ohanged to a white, brittle mass, which he recognised as a compound of iron and nitrogen. Buff (Annalen, 1852, 83, 375) found an increase of 6 per cent. and RBgnault of I2 to 13 per cent. in this reaction. Fremy (Compt. rend., 1861, 52, 322) prepared iron nitride by heating anhydrous ferrous chloride in a stream of dry ammonia. The compound thus obtained, according to Fremy, contained 9.3 per cent. of nitrogen, from which he calculated the formula Fe,N2. The 11.5 per cent. of nitrogen found by Despretz corresponded to that required for the formula Fe,N. From these results, it might be concluded that nitrogen, like carbon, was able to combine with iron in several proportions t o form compounds which would alloy with free iron, Stahlschmidt (ZOC. cit.), however, came to the conclusion that nitrogen combines with iron in a perfectly definite ratio to form a substance of the formula Fe,N, and that all the nitrides previously prepared containing less nitrogen than required by this formula must be looked upon as mixtures of this nitride of definite composition with pure iron. According to Rogstadius (J. pr. Chern., 1862, 86, 307) and Briegleb and Geuther (AnnaZen, 1862, 123, 228), finely divided iron prepared from ferrous oxalate or by the reduction of ferric oxide in hydrogen, takes up about 2 per cent, of nitrogen at the ordinary temperature or by continuous heating in nitrogen. Stahlschmidt was not able t o prepare iron nitride in this way. By the electrolysis of a mixture of a ferrous salt and sal ammoniac, a shining or spongy mass separates which, according to Kramer (Arch. Pharm., 1861, [ii], 105, 284), is an iron nitride containing 1.5 per cent. of nitrogen ; according to Meidinger (Dingl. PoZyt. J., 1863, 163, 283), it is an iron ammonium alloy. The substance is-said to give off a smell of ammonia and liberates hydrogen from boiling water. It should be mentioned, finblly, that Allen (Chem. News, 1880, 41, 231), by heating soft iron wire in ammonia, obtained a product con-