Composition of some Colloidal Solutions. iW5 



poor ill colloid. The result is that the richly colloidal solution 

 forms itself into cells which may be either full of the poorer 

 solution or of uniform composition. Further, the cells may 

 he isolated or may hang together in threads or masses. 

 Granting this hypothesis it will be readily understood that 

 the damping of a disk set swinging in such a pseudo-solution 

 will depend upon several factors, (a) the internal friction of 

 the richly colloidal solution ; (h) the internal friction of the 

 matrix of poor colloid ; (c) the external friction of the viscous 

 colloidal cidl-wall against the less viscous matrix; and {d) 

 the surface-tension at the surface common to the two solutions. 

 With ijelatiiie the principal results found were these : — 



(1) Although, as is well known, the logarithmic decrement 

 of a disk oscillating in water, or other homogeneous fluid, is 

 constant, yet in a gelatine solution the decrement varied 

 considerably, even when the temperature and concentration 

 remained unchano-ed. In o'eneral the decrement increases 

 with the time during which the disk has been immersed in 

 the solution. In the case of solutions slowly cooled to the 

 temperature under observation the logarithmic decrement was 

 a linear function of this time. There did not appear to be 

 any definite maximum of decrement, but a fixed minimum 

 was shown to exist, viz., the decrement — as found by inter- 

 polation — at the moment when the plate was introduced into 

 the solution. This value was the only one which remained 

 the same from day to day and with various solutions of 

 the same strength. When the plate was taken out of the 

 solution, well washed with hot water, cooled, and reintroduced, 

 the same '^anfangsdekrement " was obtained. 



(2j Occasional disturbances, such as the passing of a 

 vehicle in the street (50 yards away) produced with honio« 

 geneous liquids no noticeable effect, but created immense 

 irregularities in the decrement given by gelatine solutions. 



(3) BeloNV a certain temperature ty, (depending on the 

 strength of the jelly) the decrement increased continuously 

 whether the plate was washed or not. Moreover, the viscosity 

 got by Poiseuille's method also increased steadily with the 

 time. Under these circumstances the introduction of an 

 already solidified portion of the jelly caused the viscosity to 

 increase more rapidly than before — an observation comparable 

 with the crystallization of a supersaturated solution of a crys- 

 talline substance on the injection of a crystal. 



(4) The logarithmic decrement of a disk swinging in a 

 dilute (1 to 3 per cent.) solution observed after a few large 

 vibrations was smaller than w^hen observed with only small 

 s win OS. 



