August 20, 1896] 



NA TURE 



0/ / 



A NEW OX VAC ID OF NITROGEN. 

 A LTMOUC.H rapid strides have been made recently in the 

 "^ choMiistry of nitrogen and its inorganic derivatives, since 

 the discovery of hyponilrous acid by Dr. Divers in 1871, no 

 new oxyacid of nitrogen has been described. In the current 

 number of the Gazzelta Chimica Ilatiani (July 31), there is an 

 account by Dr. A. Angeli of the preparation and properties of 

 the sodium and barium salts of a new acid, H.jN\0:,, which fills 

 the gap between hyponitrous and nitrous acids. The method of 

 obtaining this acid is simple and elegant. An alcoholic solution 

 of free hydroxylamine is prepared in the usual manner from 

 hydroxylamine hydrochloride and sodium ethylate, an excess of 

 the latter being taken, and to the solution after filtering off the 

 precipitated salt is cautiously added the theoretical quantity of 

 ethyl nitrate. The reaction proceeds according to the equation 

 Cdls.lJ.NO... + NHoOH = C2H5.OH + ILNjOj, the white 

 sodium salt f)f the new acid commencing to separate out at once. 

 From this salt, which on analysis proved to be NaoNjO^, the 

 barium salt is readily obtained in a pure state by adding b.irium 

 chloride to the dilute aqueous solution. These salts are both 

 moderately stable in the dry state, but are easily decomposed, on 

 boiling the aqueous solution, into the hydrate of the metal and 

 nitric oxide. The same gas is given off quantitatively on acid- 

 ifying the aqueous .solution, and hence all attempts to isolate the 

 free acid have failed. As regards the conipo.sition of this acid, 

 from its mode of formation, the formula (NO.j)NH.OH, or 

 nitro-hydroxylamine, naturally follows ; and this is to .some 

 extent cimfirmed by the fact that the j'ellovv silver salt, moment- 

 arily obtainable from the aqueous solution, is reduced in a few 

 seconds to metallic silver, and Fehling's solution is also readily 

 reduced. The existence of an acid of this composition has already 

 been indicated by Dr. A. Thum, who sliowed that hydroxyl- 

 amine .salts when oxidised by potassium per- 

 manganate in hot alkaline solution take up 

 exactly as much oxygen as corresponds to the 

 formation of Na.,N„0.j, the formula of which 



/N.bNa 

 might be 0< | . This salt, not yet 



"^X.ONa 

 isolated, is clearly isomeric with the .sodium 

 salt above described, since it suffers no further 

 oxidation on boiling with excess of potassium 

 permanganate. It would also yield only one 

 ethyl derivative, whilst nitro-hydroxylamine 

 might be expected to give the isomers 

 (NO.,).NEt.(OH) and(NO„).NH.OEt, which 

 would be readily distinguishable, and this 

 point is being followed up by Dr. Angeli. 

 He has also applied the same reaction to 

 amy! nitrite and to nitrobenzene (BcriJilc, 

 July 27). The amyl nitrite formed a sodium 

 salt, the aqueous solution of which gave a 

 yellow silver salt resembling silver hyponitritc. Nitrobenzene 

 gave a substance which is probably QH5.XO : N(OH), identical 

 with the nitroso-phenylhydroxylamine, C,;H5.N(NO).OH of 

 Bamberger. The further development of this work, which may 

 be expected to throw light on the constitution of Traube's iso- 

 nitramine derivatives, Frankland's dinitroethylic acid, and of 

 Pelouze's salt, will be looked for with much interest. 



G. N. H. 



A RESEARCH ON THE IIOUEFACTION OF 



HELIUM} 

 IVTV experiments on the liquefaction of helium were carried 

 out with a sample of that ga-^, sent to me by Prof. Ramsay 

 from London, in a sealed glass tube holding about 140 ccm. I 

 take this opportunity of rendering him my most sincere thanks. 

 In his letter I'rof Ramsay informed me that the gas had been 

 obtained from the mineral clevite, and that it was quite free 

 from nitrogen and other impurities, which could be removed by 

 circulation over red-hot magnesium, oxide of copper, soda- 

 lime, and pentoxide of phosphorus. The density of the gas 

 was 2"I33 and the ratio of its specific heats (C/t/Cf) i'6S2 ; the 

 latter figure indicating that the molecule of helium was mon- 

 atomic, as h.ad already been found to be the case with argon. 



1 Translated from the original paper, bj- Prof. K. Olszewski, in the Bitlletin 

 de lAcaiUmiciiiS Sciences de Cracm;e (or June 1896, '• Ein Vcrsuch, das 

 Helium zu verlliinigen,' by Morris Travers. 



Prof. Ramsay further informed me that the gas was only very 

 slightly soluble in water ; 100 ccm. of water dissolving scarcely 

 07 ccm. of helium. 



From the results of my earlier experiments I had been led to 

 expect that it would be only possible to liquefy helium at a very 

 low temperature ; the small values obtained for the density and 

 solubility of the gas, together with the fact that its molecide is 

 monatomic, indicating a very low boiling-point. For this 

 reason I did not con.sider it necessary to use liquid ethylene as 

 a preliminary cooling agent, but proceeded directly to conduct 

 my experiments at the lowest temperature that could be produced 

 by means of liquid air. The app.iratus employed in these in- 

 vestigations is figured in the accompanying diagram. 



The helium was contained in the glass tube, c, of the Cailletet's 

 apparatus, c. The tube, c, reached to the bottom of a glass 

 vessel, a, which was intended to contain the liquid air. The 

 vessel, a, was surrounded by three glass cylinders, 6, 6', and 6", 

 closed at the bottom and separated froin one another. The 

 outer vessel, 6", was made just large enough to fit into the brass 

 collar, o, which supported the lid, u, of the apparatus. The 

 tube, a, fitted into an opening in the centre of the lid ; the tube, 

 /, connected with an apparatus delivering liquid oxygen, passed 

 through a hole on the right. The vessel, i, was also connected 

 with a mercury manometer and air-pump by means of a T- 

 tube, />, V, one arm of which passed through the third hole in 

 the lid of the apparatus. The tube, a, was closed by a stopper, 

 through which passed the tube, <-, of the Cailletet's apparatus, 

 a tube connected with the drying apparatus, 11, «', and one 

 limb of a T-tube, by means of which the manometer and air- 

 pump could be put in connection with the interior of the vessel. 

 The lower part of the whole apparatus was enclosed in a thick- 

 walled vessel, £', containing a layer of phosphorus pentoxide. 



By turning the valve, /■, the vessel, !>, could be partially filled 



with liquid oxygen, which, under .i luLv^iut .i| to mm. of 

 mercury, boiled at about -210 C. Almost immediately the 

 gaseous air began to condense and collect in the tube, a ; a supply 

 oPfre-sh air was constantly maintained through the drying tubes, 

 ;/ and u', which were filled with sulphuric acid and soda-lime 

 respectively. When the quantity of liquid air ceased to in- 

 crease, the tap on the U-tube, it, was closed, the T-tube, /' v', 

 was connected with the manometer and air-pump, and the 

 liquid air was made to boil under a pressure of 10 mm. of 

 mercury. In order to protect the liquid air from its warmer 

 surroundings, a very thin, double wall tube, /", reaching to the 

 level of the liquid in the outer vessel, was placed inside the 

 tube a. When, as in some of my experiments, liquid oxygen 

 was used in the inner vessel, this part of the apparatus was 

 dispensed with. 



Using the apparatus I have just described, I carried out two 

 series of experiments, in which liquid air and liquid o.xygen were 

 employed as cooling agents. The tube of the Cailletet's ap- 

 paratus was thoroughly exhausted by means of a mercury pump, 

 and then carefully filled with dry helium. In the first series of 

 experiments the helium, confined under a pressure of 125 

 atmospheres, was cooled to the temperature of oxygen boiling, 

 first under atmospheric pressure ( — l82°'5), and then under a 

 pressure of 10 mm. of mercury (-210°). The helium did not 

 condense under these conditions, and even when, as in sub- 

 sequent experiments, I expanded the gas till the pressure fell 

 to twenty atmospheres, and in some cases to one atmosphere, I 



NO. 1 399, VOL. 54] 



