( 41 ) 



in the concentration of some of the salt-solutions, required by the 

 precipitation of the gelatine itself, betray themselves. I started 

 with a 10 pCt. gelatine solution, which was filtered through a 

 sievefunnel ') when warm. By adding to this the same quantity 

 of the salt-solutions to be mixed (which were generally Vio ^ Vao 

 normal) I got solutions containing 5 pCt. gelatine with the salt as 

 V20 or V40 normal. These still liquid solutions (temp. ± 30°) were 

 mixed under strong stirring and cooled quickly to the point of soli- 

 dification. I then get a perfectly transparent gelatine, more or less 

 opalescent according to the concentration and the thickness of the 

 layer, which reflect a light internally and as it seems to me also 

 show fluorescence. The formation of colloidal silver, which as we 

 know, was first made by Carey Lka in an aqueous solution, already 

 takes place in gelatine with Ag NO3 alone, especially under the 

 influence of light; it appears in a very concentrated form after the 

 addition of some formaldehyde; it is then black-brown, still perfectly 

 transparent in thin layers and homogenous with the strongest mag- 

 nifying; only on the glass wall it deposes very slowly as a metallic 

 layer. 



Without investigating the diff'erent cases more particularly, I only 

 wish to observe that I have not succeeded in keeping substances, 

 that precipitate crystalline or at all events crystallize very quickly, 

 colloidally soluted in a medium of gelatine. Calcium oxalate, barium 

 sulphate, ammonium- magnesium-phosphate and some other substances 

 form in gelatine miscroscopically correct crystals or crystalliue 

 particles. In general it seems to me that from the many cases I 

 have investigated, this conclusicm may be drawn that the visible 

 precipitation of amorphous bodies is prevented by gelatine, that of 

 crystalline bodies not or not so easily. 



Now the question is which is the degree of division of the sub- 

 stance, the size of the particles which are prevented by their origin 

 in a colloidal surrounding to join to visible matter? It is here, in 

 my opinion, not a phenomenon of suspension or emulsion; these 

 terms are applied to microscopically visible particles; and therefore 

 I have spoken of colloidal solutions in a colloid. The size of the 

 particles is undoubtedly far beyond the Hmit of the microscopically 

 visible and therefore embraces the vast field extending between the 

 molecules themselves and the particles that are visible under the 

 strongest magnifier. According to the nature of the substances and 



1) The gelatine contains a little chlorine (± 0.1 "/,, H CI) and some sulphuric acid. 

 This must be taken into account in some reactions f. i. when forming Ago Cr O4. 



