106 PRINCIPLES OF CHEMISTRY 



In regarding solutions from this point of view they come under the 

 head of those definite compounds which chemistry mainly treats of. 70 

 For this reason we will direct our particular attention to one side of 

 the subject under consideration, which touches on the essential property 



devoted. Definite compounds, Ati^R.^O and Jj^HoO. existing in a tree for instance, 

 solid form, may in certain east's be held in solutions in a dissociated state (although but 

 partially) ; they are similar in their structure to those definite substances which are. 

 formed in solutions, but nothing obliges one to think that it is such systems as, for 

 instance, Na 2 SO 4 + 10H 3 O, or Na 3 SO 4 + 7H 2 O, or Xa.>S(). 4 , that are contained in solu- 

 tions. The comparatively more stable systems J.^jH.,0 which exist in a tree state and 

 change their physical state must present, although within certain limits of temperature, 

 an entirely harmonious kind of movement of A with /^H.jO ; the property also and state 

 of systems AnH^Q and AmU^O, occurring in solutions, is that they are in a liquid 

 form, although partially dissociated. Substances A } , which give solutions, are distin- 

 guished by the fact that they can form such unstable systems .l//Ho(), but besides them 

 they can give other much more stable systems J/^H.,0. Thus ethylene, C'oll,. in dis- 

 solving in water, probably forms a system C 3 H 4 nHoO, which easily splits up into (' .,Il[ 

 and HoO, but it also gives the system of alcohol, CoH.^HoO or C,.H G O, which is compara- 

 tively stable. Thus oxygen can dissolve in water, and it can combine with it, forming 

 peroxide of hydrogen. Turpentine, C 10 H 1(3 , does not dissolve in water, but it combines 

 with it in a comparatively stable hydrate. In other words, the chemical structure of 

 . hydrates, or of the definite compounds which are contained in solutions, is distinguished 

 not only by its original peculiarities but also by a diversity of stability. A similar struc- 

 ture to hydrates must be acknowledged in crystallo-hydrates. On melting t hey give actual 

 (real) solutions. As substances which give crystallo-hydrates, like salts, are capable of 

 forming a number of diverse hydrates, and as the greater the number of molecules of 

 water (n) they (J.H 2 O) contain the lower is the temperature of their formation, and as 

 the more easily they decompose the more water they hold, therefore, in the first place, 

 the isolation of hydrates holding much water existing in aqueous solutions may be 

 soonest looked for at low temperatures (although, perhaps, in certain cases they cannot 

 exist in the solid state) ; and secondly, the stability also of such higher hydrates will be 

 at a minimum under the ordinary circumstances of the occurrence of liquid water. 

 Hence a further more detailed investigation of cryohydrates (note 58 j may help to the 

 elucidation of the nature of solutions. But it may be foreseen that certain cryohydrates 

 will, like metallic alloys, present solidified mixtures of ice with the salts themselves and 

 their more stable hydrates, and others will be definite compounds. 



70 The above representation of solutions, &c., considering them as a particular state 

 of definite compounds, excludes the independent existence of indefinite compound! ; 

 by this means that unity of chemical conception is obtained which cannot be arrived 

 at by admitting the physico-mechanical conception of indefinite compounds. The 

 gradual transition from typical solutions (as of gases in water, and of weak saline 

 solutions) to sulphuric acid, and from it and its definite, but yet unstable and liquid, 

 compounds, to clearly definite compounds, such as salts and their crystallo-hydi -ates, 

 is so imperceptible, that by denying that solutions pertain to the number of definite 

 but dissociating compounds, we risk denying the definiteness of the atomic com- 

 position of such substances as sulphuric acid or of molten crystallo-hydrates. I 

 repeat, however, that for the present the theory of solutions cannot be considered as 

 firmly established. The above opinion about them is nothing more than a hypothesis 

 which endeavours to satisfy those comparatively limited data which we ha\e for the 

 present about solutions, and of those cases of their transition into definite compounds. 

 By submitting solutions to the Daltonic conception of atomism, 1 hope that we may not 

 only attain to a general harmonious chemical doctrine, but also that new motives for 

 investigation and research will appear in the problem of solutions, which must either 

 confirm the proposed theory or replace it by another fuller and truer one. 



