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BELL SYSTEM TECHNICAL JOURNAL 



Fig. C. Distril)Utiiin of I'llKr jianiclis in snft riiMur insulation as re- 

 vealed by a transparent section. The section was cut in a microtome liy "Hash- 

 ing" the rul)I)cr with licjuid air which hardened it just sufficiently to cut prop- 

 erly. The specimen was photographed by ])olarizcd light and with sclcnite 

 plates to secure contrast between the particles and the embedding rublier com- 

 pound. Note agglomeration of the particles into large masses. The ideal con- 

 dition of distribution would be attained when each individual iiarticle is 

 surrounded by rubl)er. MagnilKalinn 720 X, 



Fig. D. Colloidal particles as seen through the ultra-microsccpc. 



(a) Polymerized particles in a phenolic resin solution. Taken with the 



cardioid ultra-microsco))C and the Lucas I'hotomicrographic canura. 



Instantaneous exposure was necessary because the particles were in 



constant motion. Magnification, 220 X. 



(b) Coloring matter in glass. The glass was colored saffranin and was 

 transparent to the eye or with any other method of microscopic vision 

 but with the slit ultra-mfcroscope the colloidal coloring matter becomes 

 visible. y\lso taken with the Lucas photomicrographic camera, a tiine 

 exposure being necessary. Magnification, HKl X. 



