EXPEKIMENTAL KNOWLEDGE OF THE PROPEKTIES OF MATTEK. 515 



found which conform almost perfectly to the gas-liquid condition, others 

 less perfectly, -while others again deviate from it in a very marked manner. 



Molecular Weiglit of Nitric Peroxide by Eaoulfs Metliod — Ramsay. 



Raoult has of late years,' by a long series of investigations, succeeded 

 in perfecting a method by which the molecular weights may, in a large 

 number of cases, be determined by observations of the degree of tempera- 

 ture by which the freezing-point, either of water or of some other sub- 

 stance, is lowered by the solution of a given quantity of the solvent. 



In the case of acetic acid as the solvent, the freezing-point of this, 

 when perfectly anhydrous and pure, is 16'68° ; dissolve in a given weight 

 of acetic acid a known small quantity of the substance whose molecular 

 weight is required ; observe the melting-point of the acetic acid with the 

 addition of this substance ; it will be found lower than 1608° ; note the 

 difference ; and assuming, as we may, that the lowering is proportional to 

 the small quantity of tbe substance dissolved, calculate the lowering of 

 the freezing-point for the solution in acetic acid of 1 part in 100 parts of 

 the acid; this amount multiplied by the molecular weight in almost all 

 cases in which the molecular weight is known is .39. This is called by 

 Raoult the molecular depression for acetic acid ; assuming now, in any 

 case, the molecular depression to be 39, it is seen that by noting the 

 depression produced by a given small weight of a substance in acetic acid 

 the molecular weight of the substance can be determined. 



Ramsay has applied this method * to find the molecular weight of 

 nitric peroxide at about 16°, by dissolving small weighed quantities of the 

 liquid in acetic acid, and finds in a series of experiments that the mole- 

 cular weight of the peroxide is always near 92 ; and that the relative 

 number of molecules of the peroxide in a given volume of acetic acid may 

 be decreased from 8"97 to 0'92 without materially altering the molecular 

 weight ; no dissociation therefore of N2O4 takes place on dilution. 



Experiments giving Points on the James Tliomson Sinuous Curve. 



Experiments have been repeatedly made in reference to the anomalous 

 condition of a liquid when in certain circumstances it can be raised in 

 temperature above, and often considerably above, its boiling-point 

 W'ithout entering into ebullition. This state of a liquid has been the 

 subject of special examination by Donny,^ by Dafour,^ and by Gernez.^ 

 In the case of some experiments of this kind there is not only the liquid 

 but the vapour above the liquid at a temperature above the boiling-point 

 of the liquid, while the pressure of this vapour hardly exceeds the 

 atmospheric pressure, and no liquid distils. These are cases where for 

 the temperature (above the boiling-point) the pressure of the vapour is 

 less than the vapour-pressure normally belonging to that temperature. 

 We have here, therefore, points on that part of the sinuous curve which 

 is convex to the axis of volumes. Such a point, as Ramsay and Toung 



' A7in. CMm. Ph. [5], 20, 1880 ; 28, 1883 ; and [6], 2, 188i ; 4, 1885 ; 8, 1886. 

 The Agenda du Chimiste for 1888 contains a summary of the princii^les and practice 

 of M. Raoult's method by himself, p. 475. 



■-■ C. S. J. June, 1888, p. 621. 



5 Ami. Chiin. Ph. [3], 10, 1846, p. 167. 



* Tbid. [3], 68, 1863, p. 370 ; [4], 6, 1865, p. 104 ; and 16, 1859, p. 470. 



* Ibid. [5], 4, 1875, p. 335 ; and 7, 1876, p. 113. 



I, l2 



