170 



sjrnmetnciil resonance curves (see I.e. p. 642) ; tliose generated by 

 paralioloid-shaped resonators or sncli as are more complicated, like 

 some hearing apparatns, are surprisingly variable '). 



A very curious siiape of resonators is offered by the familial shells, 

 found on the beach after stormy weather, and in which the mur- 

 muring of tlie rolling waves is heard. Here numerous tones coalesce 

 into a murmur. Testing them involves peculiar difficulties for the 

 very reason, that narrow conduits are not appropriated to the exa- 

 mination of high tones. Nonetheless the difficulty can be overcome 

 by exposing the measuring mirror directly to the point-shaped outlets, 

 afforded by tlie tine openings in the wall of the shell. 



Chemistry. — "The viscositi/ of colloidal solutions." By Dr. E. H. 

 BiJCHNER. (Communicated by Prof. A. F. Holt.eman.) 



According to Einstein, the viscosity of a liquid, in which a great 

 number of particles are floating, is connected with the relative total 

 volume of the particles. If the viscosif}' of the pure liquid is repre- 

 sented by :, thai of the suspension by ;', and its volume by v, if 

 further v' is the total volume of the suspended particles, then 



z' — 2 v' 



. . = 2,5- 



Z V 



This formula has been applied to gamboge suspensions by Bakcelin, 

 who obtained fairly satisfactory results; the factor had to be taken, 

 however, 2,9 instead of 2,5. Admitting the formula to be correct, 

 we may, conversely, calculate the volume of the floating particles 

 from measuremenis of the viscosity. If, then, we determine the 

 iiuml)er of ihe particles \e. g. uluamicrDscopically), ilie volume of 

 one separate panicle may even be deduced. 



The application of this formula to colloidal solutions will greatly 

 deepen our insight in the luiiure of these systems. We might feel 

 some doubt, whether Ihe suppositions, made bj' Einstein, when 

 deducing the formula, hold good in the case of colloidal solutions, 

 the particles of which are so much smaller. But Einstein himself 

 has applied it to sugar solutions, and has calculated from the result, 

 in connection with determinations of the diffusion constant, Avogadro's 

 number. The fact, that he found in this way 6,6.10", shows, that 

 his assumptions are not far from being correct. For the rest, 1 have 

 found, that even several observations on the viscosity of ordinary 



1) H. Zwaardemaker. These Proceedings, Vol. 16, p. 496. 



