September 28, 1893] 



NATURE 



525 



exceptionally interesting kind. These compounds are solid non- 

 voIili!e substances, unlike the metallic carbonyls in this respect, 

 and are represented by the general formula M„NO„, where M 

 represents either of the four metals mentioned. Their discoverers 

 propose the name metaux nitres, which perhaps may be con- 

 veniently rendered into English as nitro-metals. 



When a quantity of copper, recently prepared by the reduc- 

 tion of copper oxide in the usual manner by means of a stream 

 of hydrogen or of carbon monoxide, is exposed at the ordinary 

 summer temperature (about 25^ being the average temperature 

 of the laboratory while MM. Sabatier and Senderens were con- 

 ducting these experiments) to a current of the reddish-brown 

 vapour of nitrogen peroxide, it becomes rapidly attacked and 

 converted into a brown substance, considerable heat being at 

 the same time evolved and a large proportion of the nitrogen 

 peroxide absorbed. The brown solid substance produced is 

 found to react with great energy with water, the reaction being 

 accompanied by a copious evolution of nitric oxide, NO. .\t 

 30' reduced copper absorbs no less than a thousand times its 

 volume of nitrogen peroxide. Upon analysis of the product it is 

 found to contain about 74 per cent, of copper. A compound of 

 the composition Cu„N02 would contain 73 '4 per cent. The 

 nitrogen present was also determined directly, by heating with 

 excess of copper in a stream of carbon dioxide, the nitrogen 

 being measured over caustic potash in the ordinary manner ; its 

 amount was found to correspond closely with that demanded by 

 the above formula. 



In preparing nitro-copper care must be taken to free the 

 nitrogen peroxide from traces of the vapour of nitric acid, for 

 this acid decomposes the compound with energy, efTervescence 

 occurring and the green nitrate of copper being produced. To 

 prevent the deleterious effects of traces of admixed nitric acid 

 vapour the red fumes are allowed to pass first through a column 

 of litharge and afterwards over phosphoric anhydride. 



Nitro-copper is unalterable in dry air at ordinary atmospheric 

 temperatures. When heated in pure nitrogen it is dissociated, 

 a temperature of 90° being ample to effect the change ; nitrogen 

 peroxide is evolved together with smaller quantities of nitric 

 oxide and nitrogen, and partially oxidised copper remains. One 

 of the most useful properties of nitro-copper is that it may be 

 used for the purpose of liquefying nitrogen peroxide ; if a 

 quantity is placed in one limb of a Faraday V-tube and heated, 

 the other limb being cooled, the nitrogen peroxide liberated by 

 the dissociation rapidly collects in the liquid form in the cold 

 limb. If the tube is removed and allowed to stand a short 

 lime, re-absorption of the peroxide by the copper occurs. Water 

 reacts with nitro-copper as above mentioned with considerable 

 violence, pure nitric oxide entirely soluble in solution of ferrous 

 sulphate being briskly evolved. The aqueous solution contains 

 cupric nitrate and nitrite, and a sediment of pure copper re- 

 mains. In moist air, therefore, nitro-copper rapidly deteriorates, 

 becoming enveloped in red fumes and its surface turning green. 

 Hydrogen is without action upon it in the cold, but when heated 

 to 180° large quantities of ammonium nitrite and free ammonia 

 are produced. Dry ammonia gas reacts at the ordinary tem- 

 perature with some energy upon nitro-copper. White clouds of 

 ammonium nitrate and nitrite and of moisture first make their 

 appearance, then suddenly the mass becomes incandescent and 

 more copious clouds of ammoniacal salts and steam are pro- 

 duced, the residue consisting of copper mixed with ammoniacal 

 oxide of copper. Sulphuretted hydrogen likewise reacts at the 

 ordinary temperature with nitro-copper, heat being evolved, 

 water, sulphur, and a blue sulphide of copper being the pro- 

 ducts of the reaction. 



It would thus appear that nitro-copper is of a kindred nature 

 to the metallic carbonyls, the nitrogen peroxide being held in 

 a similar manner to the carbon monoxide of the latter com- 

 pounds, and capable of being liberated in a regular manner by 

 the dissociation of the compound by heat. The substance may, 

 in fact, be employed as a convenient means of storing nitrogen 

 peroxide, with the certainty of being able to liberate it by a 

 comparatively slight rise of temperature whenever it is desired 

 to procure some for experimental purposes. 



Metallic cobalt reduced from its oxide by means of hydrogen 

 at a temperature below redness is only difficultly pyrophoric in 

 -lir, not becoming incandescent on admission into air with any- 



ing like the readiness of iron. It burns energetically in the 



.VI, however, in nitrogen peroxide. When the nitrogen peroxide 

 v.ipour is diluted with nitrogen, the heat of the reaction is 

 modified, and the formation of nitro-cobalt occurs in a regular 



manner, as in the case of copper. It is iiecessaiyin the case 

 of cobalt to conduct the preliminary reduction in hydrogen in 

 the same tube as is afterwards used for the preparation of the 

 nitro-compound, in order to avoid re-oxidation of the metal, and 

 it is advantageous to employ as low a temperature for the re- 

 duction as possible. 



Nitro-cobalt is a black solid substance. Its reaction with 

 water is very violent, but less nitric oxide is produced than in 

 the Case of nitro-copper. The rose-coloured solution contains 

 mainly nitrate of cobalt, and a quantity of basic nitrite is found 

 amongst the residual copper. When nitro-cobalt is heated in an 

 atmosphere of nitrogen, a small quantity of nitrous fumes are 

 first evolved, then almost immediately violent deflagration, ac- 

 companied by a flame of great brilliance, occurs. The same 

 explosive deflagration occurs if, at the end of the preparation, 

 the supply of diluting nitrogen is shut off before the nitrogen 

 peroxide. When mixed with a combustible substance nitro- 

 cobalt forms a dangerous explosive. If a small quantity wrapped 

 in paper is introduced into an eprouvette filled with mercury at 

 the top of which is a little water, a violent explosion at once 

 results upon the arrival of the small paper packet at the surface 

 of the mercury, owing presumably to the heat of the reaction 

 of a portion of the nitro-cobalt with water causing sudden 

 dissociationof the whole, the organic matter of the paper burning 

 in the gaseous products of the dissociation. 



Nitro-nickel is more difficult to obtain in a pure state, for cold 

 reduced nickel reacts so vigorously with nitrogen peroxide that 

 even when the latter is largely diluted with nitrogen a partial 

 oxidation of the metal occurs. Actual incandescent combustion 

 is, however, avoided, and a regular absorption of the peroxide 

 vapour occurs. In a careful experiment a product containing 

 20 per cent, of NO., instead of the theoretical 28 per cent, was 

 obtained. Nitro-nickel closely resembles nitro-cobalt ; it is 

 a black substance which reacts with water with evolution of 

 nitric oxide, and which deflagrates with explosive force when 

 heated in a current of inert gas. 



Nitro-iron is still more difficult to isolate. When the peroxide 

 is diluted with a very large excess of nitrogen, it is quickly ab- 

 sorbed by reduced iron up to a certain point, when the passage 

 of more peroxide invariably brings about brilliant deflagration 

 and consequent destruction of the product. There is ample 

 evidence, however, that iron does form a nitro-compound of a 

 similar interesting nature to that of the nitro-compounds of 

 copper, cobalt, and nickel above described. 



A. E. TUTTON. 



PHYSICS AT THE BRITISH 

 ASSOCIATION. 



SECTION A met in the well-appointed lecture theatre of 

 the Nottingham University College. Mr. Glazebrook 

 had only just finished his presidential address when an incident 

 occurred which was of interest as showing that members meant 

 business, and were not disposed to allow the authority of the 

 chair to be questioned. Perhaps the experimental work com- 

 municated was not of striking novelty or importance, but some 

 of the informal communications and discussions — notably those 

 on electrical theory, the connection between ether and matter, 

 and the teaching of elementary physics — were of great interest, 

 especially to teachers of physics. This was largely due to the 

 active part taken by Lord Rayleigh, Profs. Fitzgerald, Carey 

 Foster, Oliver Lodge, Riicker, and other leading physicists. 

 The discussion occasionally tended to resolve itself into an ex- 

 change of ideas around the lecture-table, but as the ideas were 

 for the most part interesting (and energetically expressed) 

 members did not appear to object. At first there was an 

 occasional grumble against Dr. Lodge's innovation of starting 

 at 10 a.m., but the wisdom of the change was shown by the fact 

 that the Section had generally to sit until 2 p.m. 



At the first sitting on Thursday (September 14), after the 

 President's address, the " Report of the Committee on Solar 

 Radiation " was communicated. Observations have been made 

 with a thermometer enclosed in a non-conducting case, an image 

 of the sun being thrown upon the bulb. Simultaneous readings 

 of screened thermometers within the case were also taken, and 

 the excess of temperature noted from minute to minute. The 

 thermometer has since been replaced by a thermo-junction, 

 which works very sharply, the readings becoming steady in 

 about six minutes, whereas with the thermometer twenty 



NO. 1248, VOL. 48] 



