April 13, 1893] 



NATURE 



567 



precipitates for those substances with barium or platinic 

 chloride. Its behaviour with nitrous acid is interesting. Upon 

 adding to an acid solution of sulphuryl diamide a few drops of 

 the solution of a nitrite nitrogen is at once evolved, in the 

 cold, and sulphuric acid is formed. 



Sulphuryl diamide does not combine with acids. Alkalies 

 ajipear to be only capable of removing one amido group, con- 

 verting the diamide intosulphaminic acid, S02(NH.,) (OH). 



As described in the course of the preparation of sulphuryl 

 diamide, ammonia precipitates from a solution mixed with silver 

 nitrate a silver compound. If the precipitate is. allowed to 

 remain in contact with the excess of the reagents for some time, 

 it invariably yields numbers upon analysis which agree with 

 the formula SO.lNHAg)^ If, however, it is at once separated, 

 it is found to consist of a mixture of this salt with the salt 

 SOj(Nn.)(NHAg). 



These silver compounds of sulphuryl diamide are amorphous, 

 even after deposition from solution in hot water. When dry 

 they are white powders very slightly sensitive to light. Upon 

 heating to 200' they decompose with evolution of sulphur 

 dioxide. 



Sulphuryl diamide likewise forms a compound with mercuric 

 oxide when its solution is mixed with one of mercuric nitrate. 

 The composition of this precipitate, however, appears to vary 

 with the degree of concentration of the solutions employed, and 

 if chlorides are present a precipitate is only obtained with a 

 very large excess of mercuric nitrate. Mercuric chloride pro- 

 duces no precipitate at all. 



A somewhat similar lead compound is also formed when lead 

 acetate is added to a mo.lerately concentrated solution of 

 sulphuryl diamide. 



Sulphuryl Imide. 



As previously mentioned, when sulphuryl diamide is heated 

 for a considerable time above its melting-point it loses ammonia 

 and becomes converted into sulphuryl imide : 



SO,(NH.,), = NH, -f SO,NH. 



The best temperature for the rapid production of sulphuryl 

 imide is 200° -210 \ The evolution of ammonia at this tempera- 

 ture is very vigorous, occurring with much frothing, but after 

 a time dimini;>hes and finally ceases, the mass becoming eventu- 

 ally solid. To purify it from impurities the solution in water 

 is treated with a solution of silver nitrate when the silver com- 

 pound of sulphuryl imide, SO._,NAg, is precipitated, :md maybe 

 recrystallised in long acicular crysials, first from water slightly 

 acidified with nitric acid, and finally from pure water. 



Upon decomposing the sdver compound with the calculated 

 quantity of diluie hydrochloric acid an aqueous solution of free 

 sulphuryl imide is obtained, which reacts strongly acid, and 

 liberates carbon dioxide from carbonates. Upon evaporation, 

 however, it decomposes, and deposits hydrogen ammonium 

 sulphate. Even evaporation in vacuo is sufficient to decompose 

 it, so that crystals of the imide itself have not been obtained. 

 It exists, however, in the solid form, although somewhat con- 

 taminated with smaller quantities of other products, in the 

 residue obtained by heating sulphuryl diamide as previously 

 described. 



Salts of sulphuryl imide, however, are readily obtained, 

 either by decomposition of the silver salt with metallic chlorides, 

 or by the neutralisation of solutions of sulphuryl imide with 

 metallic oxides or carbonates. 



I he potassium salt, SOjNfK, was obtained in the form of 

 well developed colourless crysials by adding a quantity of the 

 silver salt to a hot solution of the calculated quantity of potas- 

 sium chloride, removing ihe precipitated silver chloride by fil- 

 haiion, and evaporating the solution. Hoth the solution and 

 the salt are very stable; it requires long boiling with acids to 

 convert it into sulp'iuric acid. When the dry salt is heated it 

 (lecon)poses with con.siderable violence and production of flame. 

 Nitrogen and sulphur dioxide escape, and potassium sulphate 

 and sulphiie are left. 



The sodium salt, SO^NNa, obtained by neutralising a solu- 

 tion of sulphuryl imide with caustic soda and subsequent 

 evaporation, forms small crystals, which decompose* upon heat- 

 ing in a manner similar to the crystals of the potassium salt. 



The ammonium .salt, SO.^NNII^, isomeric with sulphuryl 

 diami<lt', was likewi>e obtained in colourless needles by neu- 

 irali-salioii of the free imide with ammania. It is interesting to 

 note that this substance is not capable of being converted into 

 its isomer by repeated crystallisation, but is partially so con- 

 NO. 1224, VOL. 47] 



verted by rapidly heating it to its melting-point over a small 

 gas flame. 



Acicular crystals of a hydrated barium salt, (S0jN).^Ba.2H.p, 

 have been obtained by saturating a solution of the imide with 

 barium carbonate and afterwards adding alcohol ; also needles 

 of a lead salt and a green amorphous copper salt. 



The acid character of sulphuryl imide, so different from the 

 neutral nature of sulphuryl diamide, is thus seen to be quite 

 conclusively established. A. E. Tutton. 



THE DENSITIES OF THE PRINCIPAL 



GASESy 



TN former communications ("Roy. Soc. Proc," February, 



^ 1888 ; February, 1892) I have described the arrangements 



by which I determined the ratio of densities of oxygen and 



hydrogen (15-882). For the purpose of that work it was not 



neces.sary to know with precision the actual volume of gas 



weighed, nor even the pressure at wlych the containing vessel 



was filled. But I was desirous before leaving the sut^ject of 



ascertaining not merely the relative, but also the absolute, 



densities of the more important gases— that is, of comparing 



their weights with that of an equal volume of wa'er : 



To elTect this it was necessary to weigh the globe used 



to contain the gases when charged with waier, an operation 



1 not quite so simjile as at first sight it appeirs. And,- further, 



! in the corresponding work upon the gases, a precise absolute 



I specification is required of the temperature and pressure at which 



I a filling takes place. To render the former weighings available 



I for this purpose, it would be necessary to determine the errors of 



' the barometers then employed. There would, perhaps, be no 



great difficulty in doing this, but I was of opinion that it would 



be an improvement to use a manometer in direct connection with 



the globe, without the intervention of the atmosphere. With 



respect to temperature, also, it was thought better to avoid all 



further questions by surrounding the globe with ice, as in Reg- 



I naull's original determinations. 



The Manometer. 

 ' The arrangements adopted for the measurement of pressure 

 must be described in some detail, as they offer several points of 

 novelty. 



The object in view was to avoid certain defects to which 

 ordinary barometers are liable, when applied to absolute 

 measurements. Of these three especially may be formu- 

 lated : — 



(a) It is difficult to be sure that the vacuum at the top of the 

 mercury is suitable for the purpose. 



{b) No measurements of a length can be regarded as satisfac- 

 tory in which diff"erent methods of reading are used for the two 

 extremities. 



{c) There is necessarily some uncertainty due to irregular re- 

 fraction by the walls of the tube. The apparent level of the 

 mercury may deviate from the real position. 



{d) To the above may be added that the accurate observation 

 of the barometer, as used by Regnauk and most of his successors, 

 requires the use of a cathetometer, an expensive and not always 

 satisfactory instrument. 



The guiding idea of the present apparatus is the actual appli- 

 cation of a measuring rod to the upper and loA'er mercury sur- 

 faces, arranged so as to be vertically superposed. The rod 

 AA, fig. I, is of iron (7 mm. in diameter), pointed below B. 

 At the upper end, C, it divides at the level of the mercury into 

 a sort of fork, and terminates in a point similar to that at B, and, 

 like it, directed do>vnwards. The coincidence of these points 

 with their images reflected in the mercury surfaces, is observed 

 with the aid ot lenses of about 30 mm. focus, held in position 

 upon the wooden framework of the apparatus. It is, of course, 

 independent of any irregular refraction which the tube may 

 exercise. The verticality of the line joining the points is tested 

 without difficulty by a plumb-line. 



The upper and lower chambers C, B are formed from tubing 

 of the same diameter (about 21 mm. internal). The upper 

 communicates through a tap, D, with the Toppler, by means of 

 which a suitable vacuum can at any time be established and 

 tested. In ordinary use, D stands permanently open, but its 



' Abstract of a paper read by Lord Uayleigh before [the Royal Society on 

 March 23. 



