C. E. Linebarger — Nature of Colloid Solutions. 219 



character of the molecule. However, the facts that the 

 solutions of colloid substances do not have an appreciably 

 higher boiling point than water nor a lower freezing point, and 

 that, in dissolving a colloid, no change of temperature takes 

 place, or, at least, but a very slight change, seems to indicate 

 that a colloid solution is not a solution in the ordinary sense of 

 the term, but rather a mechanical mixture, an emulsion, the 

 colloid being held in a state of suspension in the water. 



In the last few years, able investigators have occupied them- 

 selves with the subject, and their conclusion has pretty gen- 

 erally been that a colloid solution is really only an emulsion, 

 i.e., a suspension of the finely-divided colloid in the solvent. 

 Most of the experiments have been carried out with solutions 

 of colloid silver. But silver has the property of assuming so 

 many allotropic forms, as shown by the researches of Carey 

 Lea, that it is hardly justifiable to apply the deductions drawn 

 from the phenomena exhibited by it to other colloid sub- 

 stances. Muthmann* describes two experiments which to his 

 mind are convincing proof that colloid silver forms a " suspen- 

 sion " or emulsion with water and not a true solution. 



If a solution of colloid silver be mixed with a solution of 

 gum arabic, by adding alcohol, bo.th silver and gum arabic are 

 precipitated, although alcohol does not precipitate a solution of 

 colloid silver alone. According to Muthmann, the explanation 

 of the phenomenon is that the finely-divided silver held in sus- 

 pension is dragged down by the gum arabic when alcohol is 

 added. But Carey Lea states that a solution of litmus in water, 

 which every one admits to be a true solution, mixed with a 

 solution of gum arabic is also precipitated by alcohol. Muth- 

 mann' s experiment can then hardly be said to prove the exist- 

 ence of colloid solutions differing from crystalloid solutions in 

 that particular. 



In the second experiment, Muthmann let a solution of col- 

 loid silver freeze. After melting, the originally red color of 

 the solution had changed to a black, and it was possible by 

 means of a good microscope to distinguish small particles of 

 silver so finely divided, however, that after standing for a week 

 but a portion settled down. Yet this experiment does not 

 prove that the colloid silver is held in suspension in the water. 

 It only shows that, by freezing, the silver is made to pass into 

 a state of greater molecular aggregation, so that the "tagmas"f 

 formed are visible under the microscope. I have frozen solid 

 a solution of colloid tungstic acid, without that the properties 

 of the solution were in the least changed. At any rate, colloid 



* Ber. der d. chem. Gesellschaft; xx, 983, 188*7. 



f By " tagma" is understood a combination of molecules, i. e., a molecule made 

 up of several other molecules. See Pfeffer's " Osmotische Untersuchungen," p. 32. 



