Spread of Liquids on Solid Bodies. 



427 



14. Influence of the velocity of the falling drops upon the 

 thickness of the thin films of liquid. 



The time of discharge of the electroscope appears to vary, 

 amongst other conditions, according as the drops have formed 

 swiftly or slowly. 



On two siphons of equal diameter (1*006 millim.) (see § 4) 

 there were formed respectively 10 drops and 40 drops of water 

 in a minute, of 19 mgrms. and 19*67 mgrms. weight each ; 

 so that in one minute about 3*28 square centims. and 14*15 

 square centims. of free surface of liquid w r ere respectively 

 formed per minute. 



As before, the times of discharge t and r of the gold-leaf 

 electroscope were determined for a distance of 8 millims. be- 

 tween the platinum electrodes, without and with drops of 

 water, upon a clean glass plate. The edge-angle w T as also 

 measured at the same time, according as the drops were formed 

 slowly or rapidly. 



Z signifies the time which had elapsed since the cleansing 

 of the glass plate. 



Table XI. 



Water— Plate Glass. 



z. 



Slowly. 



Eapidly. 



Time of 



before 



depositioi 



Iischarge 



after 

 i of drop. 



Edge- 

 angle. 



e. 



Time of 

 discharge. 



T. 



Edge- 

 angle. 



e. 



Oh. 



3 



2 



; 



5 34 



0-82 



3 20 



Oh. 



1-6 



1 



7 36 



01 



7 15 



8 days 



14 



75 



8 10 



8-5 



7 20 



8 „ 



9-5 



60 



9 



65 



8 11 



"Whence it appears that a rapidly formed drop of water 

 spreads upon a freshly cleansed glass plate in a thicker film 

 than a slowly formed drop of water. The difference is imper- 

 ceptible in old surfaces of glass cleansed some time previously. 



The edge-angle appears to be less for rapidly-formed than 

 for slowly-formed drops. 



In the case of aqueous solutions of calcium chloride 

 (o-= 1*1639), potassium carbonate (cr = 1*4444), and concen- 

 trated sulphuric acid, I have not been able to prove with 

 certainty this difference of time of discharge between rapidly 

 and slowly formed drops. In the case of the solutions of 

 potassium carbonate and concentrated sulphuric acid, t was 

 found greater than t ; hence the time of discharge of the 



