^^OCTOBER 23, 1890] 



NATURE 



eiK 



in the plane of the sails, "it is possible, by a slight mental 

 effort, to change the apparent direction of rotation, and back 

 again." 



A similar effect I have often observed, but it seems in no way 

 dependent on the will. Look, for say 30 seconds, steadily at 

 the revolving disks of an anemometer ; they will soon reverse 

 their apparent direction, whether you wish it or not. Continue 

 till to gaze, and that reversed direction will be changed back. 



All whom I have asked to try this experiment felt the effect 

 to be involuntary. The changes take place not gradually or 

 confusedly, but distinctly and with decision. The fact is plain ; 

 the explanation not so simple. Hercules Macdonnell. 



4 Roby Place, Kingstown. 



Earthquake Tremors. 



Permit me to say that Mr. John Perry, in his criticism 

 ^October 2, p. 545) of my "Method of observing the Phenomena 

 of Earthquakes," has assumed that the phenomena observed 

 were due to vertical displacement ; whereas they were probably 

 due to a swaying of the building in which the observations were 

 made. 



This assumption seems also to have been made in the case 

 of the man mentioned by Mr. Wire in your last issue (p. 593). 



Marine Villa, Shanklin, I.W., H. G. DixON. 



October 18. 



A Ball of Fire. 



At about 12.5 last night I was going through the street at 

 Milverton, and saw a bright light about south of me. I saw 

 also a bright ball of fire appear through a break in the clouds 

 proceeding with great rapidity, at about the height of 45°, in a 

 direction which I estimate to be from south to north-north-east ; it 

 disappeared behind a church, and I saw nothing mnre. I am. 

 told this may be of interest, and therefore forward the account 

 to you. Charles Randolph. 



Milverton, Somerset, October 17. 



HYDRAZOIC ACID— A NEW GAS. 



A NEW gaseous compound of nitrogen and hydrogen 

 -^~^ has been obtained by Dr. Theodore Curtius, the 

 discoverer of amidogen, and its nature and properties 

 were described by him in the Chemical Section during the 

 recent scientific meetings at Bremen. The composition of 



/N 

 the gas is HN,, and its constitution H — N^ || . It is, in 



^N 

 fact, the hydrogen compound corresponding to the well- 



/N 

 known diazobenzene imide of Griess, CeH5N<^ ]| , the 



^N 

 three nitrogen atoms being united in the form of a closed 

 chain. The gas dissolves in water with great avidity, 

 forming a solution which possesses strongly acid proper- 

 ties, and dissolves many metals, such as zinc, copper, and 

 iron, with evolution of hydrogen gas and formation of 

 nitrides, the metal taking the place of the liberated 

 hydrogen. The derivation name of the gas, azoimide, is 

 somewhat unfortunate in view of its strongly acid nature, 

 and Prof. Curtius proposes the name " Stickstoffvvasser- 

 stoffsaure." Perhaps the nearest English equivalent, open 

 to the least objection, is hydrazoic acid — a name which will 

 serve to recall the many analogies which this acid bears 

 to hydrochloric and the other halogen acids. 



In studying the reactions of his recently-discovered 

 hydrazine (amidogen) hydrate, N.,H4 . H,,0, Dr. Curtius 

 found that benzoylglycoUic acid,C,iH'5CO— O— CH^COO H, 

 was decomposed by two molecules of hydrazine hydrate, 

 with elimination of water and formation of benzoylhydra- 

 zine, CfiHsCO — NH — NHg, and hydrazine acetic acid, 

 NH,— NH— CH2COOH, in accordance with the equa- 

 tion — 



C6H.,C0— O— CHjCOOH -f- 2N,H4 = 

 CfiHsCO— NH— NHs-f NH2-NH— CH2COOH + H.2O. 



NO. 1095. VOL. 42] 



Under the influence of nitrous acid benzoylhydrazine 



/NO 



forms a nitroso compound, CsHjCO— N<; , which 



^NH, 



spontaneously changes into benzoyl-azo-imide, CeHj 



/^ 

 CO — N< II , with elimination of water. 



^N 



/NO 



C0H5CO— NH— NH2-f NO— OH = CeHsCO-N/ 



^NH, 



+ H2O. 



.NO .N 



CfiH^CO-N/ = CsHsCO-N/ || + H^O. 



^NHj ^N 



Benzoyl-azo-imide decomposes, upon boiling with alka- 

 lies, with formation of benzoate of the alkali and the 

 alkaline salt of the new acid. 



CeHsCO- N< II -f 2NaOH 



'\ 



N 



.N 



= C6H5COONa-f Na— N/ || + H^O 



N 



When this sodium nitride is warmed with sulphuric 

 acid, hydrazoic acid, H — N< [I , is liberated as a gas. 



\n 



The gas is decomposed by hot concentrated oil of vitriol ; 

 hence diluted acid requires to be employed, and the gas 

 can thus only be collected in a moist state. HN3 pos- 

 sesses a fearfully penetrating odour, producing violent 

 catarrh, and dissolves in water with an avidity reminding 

 one of hydrochloric acid. The solution also bears a sur- 

 prising resemblance to aqueous hydrochloric acid ; for, on 

 distillation a concentrated acid first passes over, and 

 afterwards a more dilute acid of constant composition. 

 The aqueous solution possesses the odour of the free gas, 

 and is strongly acid to litmus. With ammonia gas, 

 hydrazoic acid gas forms dense white fumes of the am- 



monium salt, N4H4 or NH4 — Nc' || , a compound which 



N 



is completely volatile below 100°, and which crystallizes, 

 but not in crystals belonging to the cubic system, in this 

 respect indicating its different constitution to ammonium 

 chloride. The aqueous solution rapidly evolves hydrogen 

 in contact with zinc, copper, iron, and many other metals, 

 even when largely diluted. As in the case of hydrochloric 

 acid, the silver and mercurous salts are insoluble in water, 

 the others being generally readily soluble. As the acid 

 possesses feebly reducing properties, solutions of many 

 of its metallic salts, the copper salt for instance, yield 

 precipitates upon boiling of compounds of the lower 

 oxides of the metals. The barium salt, BaN^, crystal- 

 lizes from solution in large brilliant anhydrous crystals. 

 With silver nitrate the aqueous solution of the acid or 

 a soluble salt yields a precipitate closely resembling 



silver chloride in appearance. Silver nitride, Ag — N; || , 



does not, however, darken when exposed to light, and is 

 further distinguished from silver chloride by its fearfully 

 explosive properties. During the course of his description 

 at Bremen, Prof. Curtius placed a quantity of this salt 

 less than 0001 gram in weight upon an iron plate, and 

 then touched it with a heated glass rod. A sharp and 

 loud detonation resulted, and the plate was considerably 

 distorted. The mercurous salt, HgjNg, is likewise very 

 explosive. The metallic salts are readily converted into 



