320 BELL SYSTEM TECHNICAL JOURNAL 



Composition and Structure of Hevea Latex.^ A. R. Kemp. Data and 

 present views relating to the composition and structure of the latex 

 particles are presented. The number of particles in one gram of 40 

 per cent latex was calculated to be 7.4 X 10^^ on the basis that they 

 have an average particle mass of 0.054 X 10"^^ gram (from the micro- 

 scopic data of F. F. Lucas, page 146). 



A study was made of the effect of several factors on the water content 

 of rubber in pressed coagulum from fresh and treated latices. The 

 average value for the water of retention of rubber coagula from fresh 

 latex was found to be about 1 1 per cent, increasing to about 22 per cent 

 in the case of old latex and deproteinized rubber from alkali-treated 

 latex. This water appears to be held mechanically in the colloid hydro- 

 carbon structure of the latex particles. 



The particle structure of sheet rubber is discussed and it is suggested 

 that plasticization by milling involves the conversion of the gel hydro- 

 carbon shell on the rubber particles to sol rubber through oxidation. 



Ultraviolet Microscopy of Hevea Rubber LatexJ' Francis F. Lucas. 

 Samples of bulk rubber latex received in sealed cans from two sources 

 have been investigated by means of the ultraviolet microscope. The 

 advantages of the ultraviolet microscope are (a) an enormous increase 

 in resolving power, {b) selective absorption of the ultraviolet light by 

 many substances, and (c) the ability to section optically very small 

 objects suited to the purpose. 



Brief descriptions of the apparatus and technic are given. Artifacts 

 have been minimized in the preparation of the slides. A multitude of 

 particles bordering on colloidal dimensions have been clearly resolved. 

 Particle size measurements, including complete tabular data and a 

 particle size distribution curve for each specimen, are given. Ap- 

 proximately 90 per cent of the particles are 0.50 micron or less in 

 diameter. The shape of the latex particle appears predominantly 

 spherical, although elongated particles and irregular shaped particles 

 are found. Optical sections in some cases show these to be groups of 

 particles; two particles may coalesce to form one. Many of the 

 smaller particles appear to lose their electrical charges and become 

 attached to larger particles. Possible effects of ultraviolet radiation 

 are discussed. 



Dielectric Losses in Polar Liquids and Solids.^ S. O. Morgan. 

 Dielectric loss is the energy dissipated as heat in a dielectric when it is 

 in an electric field. Losses due to dipoles represent only one of a num- 



* Indus, and Engg. Chem., February 1938. 

 ^ Indus, and Engg. Chem., February 1938. 

 8 Indus, and Engg. Chem., March 1938. 



