230 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 



chains attached. The silicones have many very useful properties. 

 They can be used as insulating lacquers, permitting electrical motors 

 to be built for operation at much higher temperatures than with or- 

 ganic insulators. Silicone rubber can be made, especially for use at 

 higher temperatures than those withstood by ordinary natural rubber 

 or synthetic rubber. Some of the silicone oils have a very valuable 

 projDerty, that of changing their viscosity only a small amount with 

 change in temperature — a property that seems to be due to the tend- 

 ency of the molecules to coil into a roughly spherical shape at low 

 temperatures, and hence to roll over one another relatively easily, 

 whereas at higher temperatures, at which the molecules uncoil, they 

 become entangled with one another, and thus overcome in large part 

 the normal tendency of a liquid to show a pronounced decrease in 

 viscosity with increase in temperature. 



The chemistry of fluorine has made great progress in recent years. 

 The valuable properties of new compounds of fluorine depend on the 

 volatility of fluorine compounds and the low chemical reactivity of the 

 carbon-fluorine bond. Useful fluorine compounds include the f reons, 

 such as CF2CI2, which are used as the fluid in refrigerating machines 

 and as nontoxic solvents for insecticides and other solutes, and the 

 fluorine-carbon high polymers, such as the extremely unreactive plastic 

 that is formed by the polymerization of tetrafluoroethylene. 



An interesting recent development in inorganic chemistry is that 

 of new tecliniques for growing large crystals for special purposes. 

 During the war it was found possible to grow large crystals, weighing 

 many pounds, of such substances as ethylenedi ammonium tartrate, 

 valuable because of their piezoelectric properties, which find use in 

 radar and other fields of modern physics. In Germany, an interest- 

 ing technique of growing large crystals of synthetic mica was de- 

 veloped, a technique which depends for its success on the orientation 

 of the growing crystal in a strong magnetic field. 



ORGANIC CHEMISTRY 



The art of organic chemistry and the science of organic chemistry 

 have moved along steadily hand in hand. Organic chemists develop 

 a feeling for the chemical properties of the many substances with 

 which they work which goes far beyond the systematized theoretical 

 knowledge that they can express ; but the theory of organic chemistry 

 has nevertheless now developed to such a state that the science is no 

 longer a mysterious one, purely an art whose practice depends on the 

 application of empirical rules. It is now possible for the organic 

 chemist to use his knowledge of molecular structure to predict, with 

 some confidence, that certain reactions could be carried out to produce 

 products with certain desired properties. One most interesting appli- 



