EXPERIMENTS ON LIQUID DROPS, GLOBULES, 



AND COLUMNS. 



By CHAS. R. DARLING, A.R.C.Sc.L, F.I.C. 



I. 



Before the advent of the nineteenth century, the 

 number of liquids available for scientific investiga- 

 tion was limited to water, alcohol and other products 

 of fermentation, naturally-occurring oils, and a few 

 obtained by chemical means. Now, thanks to the 

 advances made in organic chemistry, the number of 

 available liquids has been greatly increased ; but 

 although the' chemical properties of the newer 

 liquids are well known, very scanty 

 attention has been paid to their 

 physical properties. Hence the liquids 

 used in the ensuing experiments, 

 although familiar to the chemist, 

 would probably be designated " rare" 

 liquids by the physicist, because their 

 constants do not appear in ordi nan- 

 physical tables. The present articles 

 will be devoted to a description of 

 some of the remarkable physical pro- 

 pertiesof certain organic liquids, which 

 have been investigated by the writer 

 during the past two years, more 

 especially svith regard to the formation 

 of drops, spheres, and columns ; and 

 the strange movements of globules on 

 a water surface. 



The Formation of Drops 



and Spheres. 

 In the issue of " Knowledge " 

 for January, 1911, the author des- 

 cribed an experiment for producing 

 automatically large drops of aniline 

 under water, the process being 

 enable the details of formation 



Figure 54. 



Apparatus for forming large, 

 trolled drops of liquids. 



sufficiently slow to 

 to be seen with the 

 naked eye. The experiment was based on the fact that 

 aniline is denser or less dense than water at different 

 temperatures, and from the standpoint of studying 

 the beautiful changes in shape undergone by parting 

 drops, suffered from the defect that the formation 

 was not under control. In order to produce a drop 

 which may be made to enlarge to considerable 

 dimensions, and to break at will, it is necessary to 

 run the liquid used into water from a vessel con- 

 trolled by a tap, and to employ a liquid only slightly 

 denser than water at the prevailing temperature. 

 After many trials, the author has found that the 

 liquid orthotoluidine is in every way suitable for 

 the purpose. As sold commercially, this liquid 

 has a deep red colour : is insoluble in water ; and at 

 24°C has exactly the same density as water at 24°. 

 Above this temperature orthotoluidine is lighter than 

 water, whilst below 24° it is heavier ; and as the 

 equi-density temperature is near to that of the 



atmosphere in a room, the experiment may be con- 

 ducted with the minimum of trouble. 



The apparatus requisite for the complete stud}- of 

 drops under control is extremely simple, and is 

 sketched in Figure 54. A funnel, furnished with a 

 tap, and having the stem widened at the extremity 

 to a diameter of three or four centimetres, is arranged 

 so as just to touch the surface of water contained in 

 a flat-sided glass vessel about fifteen 

 centimetres high, 12-5 centimetres 

 wide, and 7 ■ 5 centimetres deep — 

 exact dimensions being of no import- 

 ance. The water in the vessel should 

 be at a temperature of about 20°C, 

 and orthotoluidine allowed to flow in 

 slowly from the tap. A large drop 

 then gradually forms at the end of 

 the stem of the funnel, and by closing 

 the tap at any time the outline of 

 the drop may be examined at leisure. 

 Control ceases when the constricted 

 neck becomes narrow, and the drop 

 then slowly breaks away, a secondary 

 drop, as usual, being formed from the 

 neck itself. The accompanying 

 Figures — 55 to 61 — from photographs 

 by the writer and Mr. B. Abel, show 

 several stages in the formation of a 

 drop of orthotoluidine, controlled as 

 described. Figures 60 and 61 are 

 specially interesting as showing the 

 recoil after the partition of the 

 drop, both the portion clinging to the stem and the 

 separated drop being flattened ; and the secondary 



drop, which is seen elongated 



to have recoiled in Figure 

 approximately one-tenth of a 



in Figure 60, is seen 

 61. An exposure of 

 second was given, the 

 vessel being illuminated by an arc-lamp. It is easy, 

 by this method, to obtain drops three or four 

 centimetres in diameter, if the instructions given 

 above be carefully followed. 



An interesting modification of the 

 the production of inverted or rising 

 may be accomplished by bending 

 the funnel into a parallel branch, 

 Figure 62. The widened end is then 

 water at about 35°C to a depth of three inches, and 

 the tap of the funnel opened so as to allow the 

 orthotoluidine to flow slowly. As the liquid is 

 warmed to a higher temperature than 24°C in pass- 

 ing through the stem, it becomes of less density 

 than the surrounding water ; and on escaping the 

 drops, therefore, rise to the surface. The general 



experiment is 

 drops, which 

 the stem of 

 as shown in 

 immersed in 



52 



