ELECTRON MICROSCOPY 



(b) Compounds of basic oxygen: i.e., com- 

 pounds of a certain complexity and capable 

 of forming oxonium salts also react (for 

 example coumarin). These are rare by com- 

 parison Avith the compounds of basic nitro- 

 gen, but in a general test it should be remem- 

 bered that some organic bases do exist which 

 do not contain nitrogen. 



The reagent: Gold chloride crystals 

 (HAuCU-SHaO) 1 g (makes about 1.3 g 

 HAuBr4); HBr (40%) 1.5 ml; H2O 1.0 ml; 



syrupy (85-88%) H3PO4 to make 20 ml. 

 This may be named in short, HAuBr4 in 

 H3PO4 ; or in more detail as 1.3 HAuBr in 

 syrupy H3PO4, (20). 



Excellent crystals for identification tests 

 may be obtained with aminoacetic acid, 

 betaine, glutamic acid, urea, acetamide, 

 etc., as well as with many sympathomimetic 

 drugs and other substances. 



Charles C. Fulton 



Electron microscopy 



AEROSOLS CONTAINING RADIOACTIVE 

 PARTICLES 



The electron microscope is an ideal tool 

 for the analysis of aerosol particles. This per- 

 tains especially to particles with submicronic 

 dimensions down to 0.002 micron (2 X 10"^ 

 cm). Electronoscopic observations provide 

 data on size, shape, aggregation tendencies 

 and population density of the particles. In 

 addition it may be possible to obtain electron 

 diffraction data as a means for chemical 

 identification (1). Correlation of electrono- 

 scopic observations with data obtained by 

 other analytical methods makes possible a 

 complete description of a particular aerosol. 

 The purpose of this article is to describe the 

 electron microscopic appearance of particles 

 from aerosols containing Sr^'^S04 , Ru^'^'Oa , 

 or Pu23902 . 



Methods 



Particles from the various aerosols were 

 collected directly on "Formvar" coated elec- 

 tron microscope supporting grids or on mem- 

 brane filters. In the latter case the particles 

 had to be transferred to coated grids before 

 observation in the electron microscope was 

 possible. This was accomplished by a modi- 



fied Kalmus technique (2). Each aerosol was 

 represented by an appropriate number of 

 specimen grids (minimum of six grids per 

 aerosol) to provide a statistically valid sam- 

 ple of particles. All specimen grids used were 

 preinspected for cleanliness, or pre-shadowed 

 to delineate contaminations. 



Screens representing the various aerosols 

 were surveyed in the electron microscope 

 and appropriate fields were photographed at 

 magnifications of 2,000X, 6,500X, and/or 

 10,000 X. The electron micrographs illus- 

 trating this report are photographic enlarge- 

 ments. 



Size distribution data were obtained by 

 measuring several hundred particles chosen 

 at random on the prints representing the 

 different samples. The particles were all 

 measured in the same direction. 



Observations and Discussion 



Description of the Particles. Strontium 

 Sulfate. The particles obtained from aerosols 

 containing Sr^''S04 are characteristically in 

 the form of needles. Tj^pical examples are 

 illustrated in Fig. 1. For the most part the 

 needles occur in clusters. The dark cuboidal 

 or spherical material noted in these micro- 

 graphs may be undissolved membrane filter 



72 



