Dr. Schweieffer on Prut". Dcebereiner's 



ns 



a liquid, to have attained the limit of the infinite even in idea. 

 On the other hand, we find, when we take experience for our 

 guide, one and the same body — as for instance, acetic acid — at 

 one and the same temperature appear as well in a crystalline 

 as in a liquid or gaseous form, those states being dependent 

 only on various pressures of the atmosphere *. And we knew 

 long since, that in some experiments on the polarisation of 

 light, some liquids produce effects which are dependent upon 

 a crystalline double refraction of the rays of light; as for in- 

 stance, camphor has in its solid state a double refraction, 

 and reproduces, in the well known experiment of Malus, the 

 double image which has disappeared ; but it retains that pro- 

 perty in its liquid state, of which I have convinced myself by 

 an experiment instituted expressly for that purpose. The 

 same is known to be the case with camphor dissolved in spirits 

 of wine. Even polarisations like those of crystals of attrac- 

 tive or repulsive axes appear in some liquids. The crystal- 

 line nature of the differentials of many liquids can be proved, 

 therefore, by direct experiment. In this our differential cal- 

 culus of physics, the step is therefore unavoidably taken to 

 consider the elastic fluids under the same point of view as I 

 have done in the former series of this work (see vol. v. p. 60). 

 Indeed this assumption, though at variance with the some- 

 what surprising notion commonly entertained on that subject, 

 has already obtained the assent of several exact chemists f. 



* The experiments of Mr. Perkins on this subject will soon be made known. 



-f- Compare, for instance, the Review of the principal Features of the pre- 

 sent State of Chemistry ; by Professor Von Ittner, Freiburg, 1823. On the 

 other hand, I must be excused for not paying any attention to what M. 

 Osann has stated in regard to my theory, in his Treatise on those substances 

 which congeal when heated, and become liquid again upon cooling, in- 

 serted in Gilbert's Annals, vol. lxix. p. 283 — 300. M. Osann completed 

 the greater part of this Treatise under my direction, and made most of 

 the experiments contained in it in my presence, and in my laboratory. 

 But it is to be wished that he had given a greater degree of perfection to 

 his more recent labours, and particularly that lie had paid more attention 

 to the diminished solubility of lime, as also of several other substances 

 at an elevated temperature. I must also refer him to some other things ; 

 particularly to the remarkable observation made by M. Bucholz on the 

 crystalline precipitate of the sub-nitrate of bismuth, even when dissolved 

 in an excess of water, by the mere increase of heat ; which latter phaeno- 

 menon M. Osann has cited, in p. 300, in a very incorrect manner, because 

 he has not taken the trouble to read attentively the passage cited from 

 Bucholz' s Contributions to the Extension of Chemistry, No. II. p. 60, and 

 No. II f. p. 1. M. Osann has in every respect been precipitate in his 

 publication. He has overlooked, in his hurry, that the theory which he 

 considers as peculiarly his own, is the very same as that of M. Gay-Lussac, 

 which I had mentioned in my Essay, which has been attacked, but scarcely 

 read, by M. Osann : a theory which was given up by M. Gay-Lussac him- 

 self in consequence of his own further experiments. 



The 



