C. Bar us — Compressibility of Colloids. 293 



ments were made with the 20^ gelatine solution, after thor- 

 ough coagulation. In two experiments I was fortunate in 

 breaking off very short mercury threads while the colloid was 

 still liquid, to indicate the nature of the strain above the 

 meniscus. In one case this drop, originally ellipsoidal in form, 

 sharpened upward as pressure increased, until at about 150 atm. 

 the conoid completely exploded, giving rise to about fifteen 

 small projectiles distributed along the lower 10 cm of the column 

 of coagulated colloid. The motion, which is extremely swift at 

 first, of the order of several meters per second, as I judge, dies 

 down gradually within 5 to 10 minutes to the merest creeping. 

 A full protocol of a similar experiment on a continuous 

 column, thoroughly coagulated after slow cooling from 100°, 

 is given in Table 6. A drop of mercury originally nearly round 

 in appearance was here also present just above the meniscus. 

 As pressure increased, accompanied by the sharpening apex of 

 the conoidal meniscus already described, the base of the drop 

 in all cases remained apparently convex, while its sides sloped 

 even more steeply than the meniscus of the column of mer- 

 cury. It may have been reentrant and the cone hollow, but I 

 did not notice this. 



Table 6. — Compression of a coagulated 20 per cent gelatine solution. 



6 



L 



P 



Remarks. 



°C 



cm 



atm 





24° 



16-325 



16 



* 





16-310 



92 



(i) 









115 



(2) 





16-310 



130 



(») 





16-305 



160 



(*) 









170 



(5) 





16-310 



200 



(6) 





16300 



265 



(<) 









300 



(8) Tube breaks. 



* The tube originally showed a good meniscus (obtained by slow cooling from 

 100°) and a detached, apparently round drop of mercury a few millimeters 

 above it. 



(1) Both meniscus and drop sharpen conoidally, with the apices directed 

 upward. 



(2) Further sharpening. The drop shoots off one little projectile, tadpole- 

 shaped, -OlS ™ long, which penetrates upward alone, very fast at first, slowing 

 up gradually to zero. The motion continues visibly several minutes. Another 

 projectile follows in the same way. Both eventually stop about 4 cm above the 

 meniscus and -5 cm apart. 



(3) Two more projectiles shot off consecutively from the drop. The two 

 former rise but slightly ; the latter come to rest below them. 



(4) The top (original) projectile now rises, tadpole fashion, to 8 cm above the 

 meniscus. The others gradually meet and coalesce, rise without meeting the 

 first. Meantime new projectiles have been shot off by the drop, which suc- 

 cessively rise, forming a close group 4 cm high. Simultaneously the very sharp 

 meniscus of the lower mercury column has been firing projectiles through the 



