SHADOW ALTORADIOGRAPIIY 



aliquot s of the acetone suspension treated in 

 the same manner as described above. 



The glass slide containing the particles is 

 shadowed with chromium at an acute angle 

 (e.g. 30°) (1). The shadowed slide is next 

 examined in the optical microscope and 

 areas of interest are recorded by stage mi- 

 crometer readings and by photomicrography. 



Following the microscopic examination, a 

 section of 5 micron nuclear track emulsion 

 stripping film (e.g. NTA for alpha-emitting 

 particles and NTB for beta-emitting par- 

 ticles) is floated over the sample and allowed 

 to dry. The latter step is performed in a 

 dark room using a series I Safelight filter. 

 The slide bearing the particles and emulsion 

 is placed in a light-tight box with a desiccant 

 for a suitable standardized time for exposure 

 at 3°C. The exposed slides are developed in 

 D-19 developer for 5 minutes, washed, fixed, 

 dehydrated and cleared, and a coverslip 

 mounted over the emulsion. The slide is re- 

 examined in the microscope and previously 

 selected areas are photographed. 



Alpha activity is manifested by star clus- 

 ters of alpha tracks (cf. Fig. la and lb). Beta 

 activity is manifested by spots of dense 

 granules (cf. Fig. 2a and 2b). Beta activity 

 may be determined quantitatively by spot- 

 diameter autoradiography (2). 



The method for differentiating radioactive 

 from non-radioactive particles is as follows. 

 A sheet of tracing paper is placed over the 

 photomicrographs or negatives of selected 

 areas of the shadowed slide before auto- 

 radiography. Particle positions are noted 

 with small circles. The tracing is next placed 

 over the photomicrograph or negatives of the 

 slide after autoradiography and activity 

 centers noted with a check mark or cross. 

 The tracing now has small circles represent- 

 ing non-radioactive particles and crosses or 

 check marks denoting radioactive particles. 

 Siriking results are obtained by superimpos- 

 ing the negatives of the areas before and 

 after autoradiography (cf. Figure 3). The 

 physical characteristics of the particles are 

 determined from the photomicrographs of 

 selected areas on the shadowed slide before 

 autoradiography. 



REFERENCES 



1. Dempster, W. T., and Williams, R. C, Anat. 



Record, 96, 27 (1946). 



2. DocKTJM, N. L. AND Healy, T. W., Stain Tech- 



nologij, 32, 209 (1957). 



3. DocKUM, N. L. and Borasky, R., Nucleonics, 



15, 110 (1957). 



R. Borasky 



Chemical microscopy 



ALKALOIDS AND ALKALOIDAL-TYPE PRECIPI- 

 TATION 



An attempt is made in the article on 

 Chemical Microcrystal Identifications to 

 keep the discussion of practical work on a 

 sufficiently general basis so that any analyti- 

 cal chemist concerned with identification 

 may be able to see some application to his 

 own work. If a consistent effort is made to 



use and develop this kind of chemical iden- 

 tification, it is usually best to work from 

 tests that are already known and satisfac- 

 tory in a restricted field, and to extend the 

 coverage first to chemically related com- 

 pounds, having the same or modified re- 

 agents, and by stages, systematically try to 

 cover entirely different groups of compounds 

 with other reagents and new crystal-produc- 

 ing reactions. 



13 



