290 C. Barus — Compressibility of Colloids. 



case the colloid is at a lower temperature (24°) as compared 

 with ether (29°), this would indicate greater compressibility 

 for the india rubber solution. Even at 100° this state of 

 things is not quite wiped out. These results thus recall the 

 case of the preceding paragraph. 



Here again, however, I do not wish to insist on these detailed 

 observations, because of manifold sources of error incident to 

 the method. The present results demonstrate all that I asked 

 of them in showing that to ascertain the effect of the colloid 

 on the compressibility of the solvent, it is necessary to use 

 some much more sensitive method than the direct capillary 

 tube comparisons of the present paper. 



Table 4. — Compressibility of ether and of an etherial solution of caoutchouc, 

 about 5 per cent by weight. 





Ether. 





Caoutchouc-ether solution. 



d,L 



P 



l/L 



6, L 



P 



l/L 



29° 



20 



•0000 



23*9° 



45 



•005 



14«57 cm 



100 



137 



7-72 cm 



123 



17 



at 20 atm 



200 



291 



at 20 atm 



195 



27 





300 



423 





286 



38 





400 



10 



540 





57 



... 



100° 



•oooo 



100° 



•021 



16'85 cm 



100 



•0357 



8*93 cm 



148 



51 



at 10 atm 



200 



•0653 



at lo atm 



221 



71 





300 



•0876 





298 



88 





400 



•1060 













6. The last two paragraphs, therefore, show in a general 

 way that the compressibility of a colloid is essentially deter- 

 mined by the solvent for a wide range of concentration and 

 throughout enormous variations of viscosity, so long as the 

 solution is liquid, however viscous it may be. In so far as 

 compressibility is decreased, the decrement will not exceed the 

 amount corresponding to the displacement produced by the 

 mere bulk of colloid present. 



The essential identity of behavior of a solvent in the pres- 

 ence or absence of dissolved colloid seems first to have been 

 definitely expressed in 1888 by von Tiezen-Hennig,* reasoning 

 from the results of electrolytic experiments. 



In this place I may add a correlative result obtained in my 

 experiments on the solution of vulcanized india rubber, f where 

 it is shown that the melting point of the coagulated colloid is 

 practically independent of the solvent contained. 



*"Ueber scheinbar feste Electrolyte," quoted by Bjerken, 1. c. 

 f This Journal, III, xlii, p. 359, 1891. 



