478 



Mr. E. Talbot Paris on the Polarization of 



3. Determination of the Dimensions of the Particles, — The 

 following methods were used to determine the size of the 

 particles : — 



(1) By observing the velocity of fall of the particles in 

 water under the influence of gravity, applying Stokes's law. 

 This method was used for the largest particles. 



(2) The number of particles per cubic centimetre was 

 determined by observing the average number in a known 

 volume illuminated in the ultramicroscope. The whole of 

 the silver was then collected by centrifuging and dissolved 

 in nitric acid, the solution being made up to a certain volume. 

 The silver having been precipitated by the addition of hydro- 

 chloric acid, the turbidity of the resulting suspension was 

 matched by precipitating silver chloride from a standard 

 solution of silver nitrate, under as nearly as possible similar 

 conditions. 



(3) The size was calculated from the speed and dimensions 

 of the centrifuge. 



4. Observations on the Polarization of the Scattered Light. 

 The observations were made with a polarimeter, the 



essential parts of which were a rectangular opening, a 

 double-image prism, and a nicol attached to a divided circle. 



•paratus is shown in fig. 5. 



Fig. 5. 



The arrangement of the 



dTr Apparatus for observing the polarization of the scattered light. 



The suspension to be examined was placed in the small 

 beaker B on the table of a spectrometer. Light from the 

 arc C is focussed by the lens L so that an almost parallel 

 beam of light passes through the liquid in the beaker. The 

 width of the beam was adjusted to about 1 cm. by means of 



