6. Barus — Compressibility of Colloids. 



287 



viscous at higher temperatures to admit of introduction into a 

 fine capillary bore. Greater difficulty is experienced with the 

 20 per cent solution. Albumen is advantageously introduced 

 in the natural state as white of egg. 



Considerable trouble was encountered in charging the tube 

 with india rubber, though a 5 per cent solution in ether was 

 manageable. The presence of traces of sulphur is apt to foul 

 the meniscus, while the absorption of water from air by con- 

 densation is unavoidable during filling. 



The remarkable volume-elasticity of water makes it a diffi- 

 cult body to observe by the present method. Thus for a 

 thread 10 cm long, the motion of the meniscus will scarcely 

 exceed \ millimeter per 100 atmospheres. For longer threads 

 and higher pressure the case is proportionately favorable, but 

 in no practical case is an accuracy of more than 3 or 4 per 

 cent to be looked for, quite aside from the compressibility of 

 the glass. The latter is best eliminated and sufficiently so for 

 the present comparisons, by examining all the samples as far as 

 possible in the same tube. For ether the case is 2 to 8 times 

 more favorable, depending on temperature. 



4. The following data, selected from a large number of simi- 

 lar experiments, will best exhibit the results obtained. In the 

 tables 6 denotes the temperature of the thread of total length 

 L in cm., while I is the decrement of length for the pressure 

 p (in atmospheres) stated. Hence l/JL, the decrement of length 

 per centimeter, is also the decrement of volume at the given 

 temperature and pressure. The solvent and colloidal solution 

 may be conveniently compared in two ways : one is to plot 

 l/L varying with p for each substance ; the other to compute 

 the mean compressibility ft within the same pressure interval 

 (usually about 200 atm.). 



Table 1. — Compressibility of water and colloidal solutions of gelatine and 



albumen in water. 





Water. 







Gelatine 10#. 



Albumen (Natural). 



d,L 



P 



l/L 



e,L 



P 



l/L 



0, L 



P 



l/L 



23° 







•0000 







m 







22° 







•0000 



1 7.4cm 



83 



037 













12*3 cm 



81 



039 





160 



075 



. 











128 



061 





226 



108 



•0000 



— 













191 



093 



100° 







100° 



•0000 









18'l cm 



83 



046 



21'l cm 116 



058 







... 



. «. - _ 





180 



098 







211 



100 







_ - _ 



_ 





244 



133 







282 



133 











Corresponding values of l/L and p are given for water, 

 gelatine and albumen in aqueous solution in Table 1. At ordi- 



