ELECTRON OPTICS 



If this is accomplished in practice there an extra dark band caused by osmium at- 

 will be new possibilities for studying crystal tached to the double bonds, 

 structures and detecting imperfections. The The RIAS workers have compared sepa- 

 images are poor Fourier projections and fail rate micrographs of multilayers made from 

 to reveal detail obtained by x-ray analysis; Cis, C22; and C36 acids salts. Periodicities of 

 but they do reveal the exact location of im- the bands show ratios of 16 to 22 to 36. With 

 perfections, thus permitting the direct study longer chain barium soaps, the lighter bands 

 of the behavior of dislocations in solids under increase in width while the dark bands (me- 

 a variety of physical conditions. tal ions) remain constant. The width of the 



Very recently, as reported in the July 4, dark bands is greater than the actual thick- 



1960 Chem. Erig. News, it has been demon- ness (2 to 3 A) of the metal ion double 



strated that electron microscopy can show sheath, but resolution of the electron micro- 



the actual structure of soap multilayers at scope goes down only to 8 to 15 A. 

 the molecular level. Two workers at the The band image of the micrographs repre- 



Research Institute for Advanced Stud\^ in sents actual ''multilayer architecture" and 



Baltimore, Md., have made micrographs that not merely interference fringes. For one 



picture highly regular sequences of Hght and thing, structures of 40, 80, or 120 double 



dark bands. And the spacing of these bands layers of soap molecules (made of saturated 



conforms with the length of fatty acid chains fatty acids) show exactly 40, 80, or 120 



that make up the soaps, they find. bands, as the case may be. Moreover, such 



This combination of electron microscopy details as line dislocations in the micrographs 



and film techniques is the first observational are noted as in the case of the metal phthalo- 



method to confirm the double-layer spacing cyanins. 

 of multilayers. Dr. Hans J. Trurnit told the references 



34th National Colloid Symposium sponsored , ,^ ^ „. ,,„ , ,;r. t^ 



1 1 4 ^01 T^- • • r ^11 • 1 ^1 • 1- Menter, J. W., "Electron Microscopy, Pro- 



by the ACS Division of Colloid Chemistry, ceedings of Stockholm Conference, Sept. 



at Lehigh University. The double spacing 1956," Academic Press, N. Y., 1957, p. 88. 



(previously derived from optical and x-ray 2. Neider, R., Ibid., p. 93. 



methods) results from a head-to-head, tail- ^- Wyckoff, R. W. G., Koninkl. Nederl. Akad. 

 to-tail arrangement when the layers are laid W^tenschappen, Amsterdam, Proc, B59, 449 



down on the surface. 



Dr. Trurnit and his associate, George George L. Clark 



Schidlovsky, build the multilayer soap films 



on methacrylic ester slides. Then they expose DISLOCATIONS IN METALS. See TRANS- 

 sample strips of the slides to osmmm tetrox- MISSION ELECTRON MICROSCOPY OF 

 ide (contrast inducer and fixing agent), im- METALS-DISLOCATIONS AND PRECIPITA- 

 bed them in the polymerizing plastic, and tION d 291 

 slice them into thin sections (about 500 A.). 



They could not use free fatty acids because of ELECTRON OPTICS: ELECTRON GUN AND 

 their solubiUty in the plastic bed. ELECTROMAGNETIC AND ELECTROSTATIC 



Dark bands in the electron micrographs lcinoco 



correspond to sheaths of metal ions in the The electron optical system of the electron 



soap layers, when the metal used has a high microscope comprises (a) an electron gun in 



enough atomic number to give electron scat- which electrons emitted from the tip of a hot 



tering. Magnesium ions do not register, but tungsten hairpin-shaped filament are ac- 



calcium, barium, and other such ions do celerated to produce a narrow conical di- 



show up. Also, unsaturated fatty acids show vergent beam of electron illumination to ir- 



147 



