MICROINCINERATION 145 



Calcium and Magnesium. The dense white ash seen in the 

 dark field is due chiefly to calcium with a smaller amount of mag- 

 nesium. Unless spectrographic means are employed, magnesium 

 cannot be identified in the presence of calcium in incinerated 

 sections. As a test for calcium, Moreau (1931) suggested dissolving 

 ash in a ''microdrop" of 0.1 N hydrochloric acid followed by tlie 

 addition of a "microdrop" of 0.1 A^ sulfuric acid in order to form 

 the needle-shaped crystals of calcium sulfate. 



Silicon. The identification of silicon can be made with assur- 

 ance since silica retains its typical crystalline structure during 

 incineration, and its double refraction when examined with polarized 

 light serves as an additional means of characterization (Policard 

 and Alartin, 1933) . The tendency of certain constituents in the ash 

 to combine with the silica in the glass slide during the heating may 

 give rise to a misleading appearance. The probability that silica and 

 calcium salts combine in the incineration process must also be 

 kept in mind. 



Iron. The oxidation of iron that occurs produces a color in the 

 ash which may vary from yellow to deep red making the identifica- 

 tion of this element relatively simple. Scott ( 1937) cautions that 

 care must be taken to avoid contamination with iron from the 

 microtome knife. A newly sharpened knife will be apt to cause the 

 most trouble. After 40-50 sections have been cut the number of 

 particles of iron left in the subsequent sections is practically negli- 

 gible. 



Lead. Exposing incinerated sections to hydrogen sulfide gas 

 has been employed by Tada (1926) and Okkels (1927) for the 

 identification of lead as its black sulfide. However, sulfides of other 

 metals are also black and the possibility of an interference of this 

 nature should be kept in mind. It is necessary to make sure that 

 carbon particles due to faulty incineration are not present before 

 the ash is subjected to the gas, since these particles and the black 

 sulfide can be easily confused. 



Uranium. Policard and Okkels ( 1930) claimed to have detected 

 uranium, by its fluorescence under ultraviolet radiation, in ashed 

 sections from animals poisoned by this element. Fluorescences may 

 be produced by impurities too, and hence this criterion is not a very 

 rigorous one. 



