February, 1913. 



KNOWLEDGE. 



53 



Figure 55. 



Figure 56. 



Figure 57. 



Figure 58. 



shape of inverted drops resembles that of 

 falling drops, the neck, as usual, giving rise to 

 a secondary small drop. 



The production of spheres of liquids demands 

 equality of density between the liquid and its 

 surroundings. Formerly, Plateau's method 

 was followed, in which spheres of oil were 

 formed in a mixture of alcohol and water 

 brought by trial to the same density as the 

 oil — a somewhat troublesome proceeding. By 

 carrying out the following instructions, spheres 

 of liquid, of any desired size, may easily be 

 obtained : — A flat-sided glass vessel, about 

 eighteen centimetres (seven inches) high, is 

 filled with water at 25°C to a height of 

 about twelve centimetres. The correct tem- 

 perature is secured by adding warm water to 

 tap water and mixing until a thermometer 

 shows 23°C. By the aid of a pipette a five 

 per cent, solution of common salt in water is 

 discharged at the bottom of the vessel, to a 

 depth of about two centimetres, this layer 

 preventing the sphere, when formed, from 

 sinking to the bottom when the temperature 

 falls. Orthotoluidine is now allowed to flow 

 gradually into the water from a tube of one 

 centimetre diameter, the end of which, to 

 commence with, is placed about two centi- 

 metres distant from the surface of the layer of 

 salt solution, but is afterwards raised gently as 

 the sphere grows in size. In this way spheres 

 two hundred cubic centimetres or more in 

 volume may be formed ; and, by raising the 

 delivery-tube rapidly, the attached sphere may- 

 be separated, and will remain floating in the 

 liquid. 



The photographs shown in Figures 62 and 

 63 illustrate the mode of formation and the 

 appearance of the detached sphere. In the 

 experiment depicted the orthotoluidine was 

 run from a burette, with a view to measuring 

 the volume of the sphere, which in this case 

 was one hundred cubic centimetres. 



Professor C. V. Boys, F.R.S., has suggested 

 a modification of the procedure which dispenses 

 with the necessity of warming the water. After 

 placing the layer of five per cent, salt solution 

 at the bottom of the vessel, the pipette is 

 again filled, and the salt solution discharged, 

 in diminishing quantities, from the bottom 

 layer upwards to within about two centimetres 

 of the surface. The orthotoluidine is then 

 allowed to flow into the centre of the vessel 

 from a tube bent so as to discharge laterally ; 

 and the sphere formed will then Moat or sink 

 until it finds a layer equal in density, in 

 which it will remain at rest. It is necessary, in 

 this case, to exercise care in grading the density 

 of the water from bottom to top by discharging 

 the salt solution slowly, and gradually rais- 



Figuue 59. 



Figure 60. 



Figure 61. 



Figures 55 to 61. Seven stages in the formation of a large drop of orthotoluidine. 



