(547) 



equilibrium solid-gas. The appearance of the first slight quantity of 

 liquid took place at — 10°. 8. The melting proceeding very slowly, 

 we have kept the mass for a long time between — 11° and — 10°. 

 At last we could observe that also the last quantity of solid substance 

 disappeared at — - 10°. 8. So no appreciable melting range appeared 

 during the melting. A comparison between the melting point found 

 by us under the saturation pressure and the melting points given in 

 the literature is found in the subjoined table. 



T A B L E IV. 



— 9° (Péligot) — 10°.95 (Bruni and Berti) 



— 9°.6 (GuYE and Drouginine) — 11°.5 to —12° (Muller) 



— 10°.14 (Ramsay) — 13°.5 (Frietsche) 

 -10°.8 (see above) 



Fi'om the above survey it appears that our value for the melting- 

 point agrees with that of Bruni and Berti, and that it lies lower 

 than the two melting-points of Ramsay and Guye, which have also 

 been found in recent times. Though as a rule decidedly the more 

 importance is to be attached to the melting-points the higher they 

 lie, at least for so far as the formation of mixed crystals is excluded, 

 yet the value found by us does not seem less probable to us than 

 the two last mentioned for the following reasons. Guye and Droüginine's 

 determination was carried out with a pentane thermometer, for which 

 a correction of about two degrees was necessary for the emerging 

 part, which can account at least for part of the found difference. 

 Ramsay determined the melting-point with a view to an investigation 

 of the constant of the lowering of the melting-point which is, of course, 

 independent of the absolute value of the melting-point ; also in the 

 apparatus used for this it will, probably, have been inevitable, that 

 a part of the thermometer emerged from the apparatus. 



Moreover we have prepared a quantity of nitrogen peroxide in 

 the way indicated by Ramsay by addition of J^jO,, prepared from 

 strong nitric acid and arsenictrioxide, to strong nitric acid and 

 phosphorpentoxide. The decoloration of the N^Og soon appears when 

 a sufficient quantity of the iNjOj formed from the nitric acid and 

 phosphorpentoxide is present. The obtained liquid was poured off 

 from the phosphoric acid formed and the rest of the PjOj, and five 

 fractions from this were received in tubes provided with capillaries 

 by distillation through a phosphor pentoxide tube. With none of 

 these fractions a final melting-point was found that lay higher than 



