171 



solutions may be represented by the same formula, as I hope to 

 show in a more detailed paper. There is, therefore, no objection to 

 the application of the formula to colloidal solutions, which, according 

 to modern theory, stand between the ordinary solutions and the 

 suspensions or emulsions, and differ from these only with regard to 

 the size of the "dissolved" particles. For the present, it is not of 

 much importance, that the value of the factor is not yet absolutely 

 settled. In this communication, I only wish to show at least quali- 

 tatively, that the colloid particles are combined with a quantity 

 of the solvent. For instance, the ultramicroscopically visible particles 

 of a ferric hydroxide solution consist of a number of molecules 

 ferric hydroxide and a number of molecules water ; these are moving 

 as an aggregate in the surrounding liquid. A great viscosity is 

 (0 be ascribed to a great volume of the colloid particles, either 

 they are very great themselves, or they take up much water. It 

 must be pointed out, that, when comparing different solutions, 

 one ought to express the concentralion in volume percentage, because 

 according to the point of view here adopted, the viscosity depends 

 only on the volume of the dissolved particles. 



The idea may also be applied to ordinary molecular solutions. 

 The fact, that tiie viscosity of solutions of electrolytes is often 

 relatively large, may be brought in connection with the property of 

 the ions, to combine with or to envelop themselves by water, a 

 faculty of which numerous investigators have furnished proof on 

 the most different grounds. In accordance with this conception, the 

 salt solutions, the ions of which show the smallest tendency to 

 hydration, exhibit the smallest viscosity. But, for the present, I 

 will not enter further into this question. 



I have only to communicate measurements of two substances, 

 molybdenum blue (MOsO,?) and iron liydroxide. I have determined 

 at 30^ and 40° the viscosity and specific gravity of some solutions 

 of varying concentrations. The values for the two temperatures diffe- 

 ring only slightly, the communication of the results at 30° will be 

 sufticient. In the subjoined table z' represents the \ iscosity of the 

 solution, that of water being taken = 1, ?'' the volume of the particles, 



v' 

 deduced from z' according to z' — '1 = 2,5 — ; v is put equal to 1 cc. 



The concentration of the solutions c is expressed in g per cc. ; d' 

 is the density thereof. As dissolved substance I I'egard the molyb- 

 denum blue, dried at 100°, respectively the ferric hydroxide : Fe(OH),. 

 The concentration of the solutions of the former is known, for they 

 are made by weighing ; the content of the latter is detei'mined iodo- 



