1864.] 



Prof. Guthrie on Drops. 



477 



as a stalagmoscope, to render evident rather than to measure a difference 

 of drop-size. 



From Table XVI. we gather the general law concerning three liquids, 

 two of which are insoluble in the third. If a liquid, A, drop downwards 

 under like conditions in succession through two liquids, B and C, then its 

 drop-size through any mixture of B and is intermediate between its 

 drop-size through B and its drop -size through C ; and the greater the 



proportion of q in the mixture, the more nearly does the drop-size of h. 



through the mixture approach to the drop-size of A through q alone. 



We have already examined the influences on the drop-size in the case 

 SLG of the density of the dropping liquid, and of its persistent and stub- 

 born cohesions respectively. Increase in the former two tends to diminish 

 the drop-size ; increase in the last to increase it. Let us examine in like 

 manner the influence of the similar properties of the medium. 



1. The density of the medium. — Increase in the density of the medium 

 is equivalent to diminution in the density of the dropping liquid, and must 

 therefore be followed by a tendency to increase in the drop-size. 



2. Stuhhorn cohesion of medium. — The resistance to displacement, or 

 stubborn cohesion of the medium, tends to keep back the drop in its place, 

 and makes it necessary for a larger quantity of the dropping liquid to ac- 

 cumulate ; that is, it increases the drop-size. 



3. Retentive cohesion of medium. — The same force of persistent or re- 

 tentive cohesion which causes a drop of a liquid to take the spherical form, 

 would also cause the liquid to give or tend to give a spherical form to an 

 irregularly-shaped volume of a solid, liquid, gas, or vacuum in it. Thus 

 gas-bubbles in liquids have an approximately spherical form, not by reason 

 of the cohesion of the parts of the gas, but by the persistent cohesion of 

 the liquid medium which moulds the gas into that form by which the co- 

 hesion of the liquid is most gratified. Hence increase in the retentive or 

 persistent cohesion of the medium tends to diminish the drop-size of the 

 dropping liquid. 



In all cases of SLL we may represent the direction of the influence of 

 the determinants by the following scheme, in which the sign + denotes a 

 tendency to increase, the sign — one to diminish the drop-size : — 



+ 



Stubborn cohesion. 



+ 



Stubborn cohesion. 

 Density. 



SLL. 



Dropping Liquid. 



Persistent cohesion. 

 Density. 

 Medium Liquid. 



Persistent cohesion. 



