CHLORIDE AND PHOSPHATE-CARBONATE 33 



tion of chloride in the presence of phosphate and carbonate by means 

 of the phosphoric acid it contains. The acid holds the phosphate in 

 solution and decomposes the carbonate. The other reagent, with- 

 out phosphoric acid, precipitates chloride, phosphate, and carbonate. 

 By comparing sections separately treated with each reagent, chloride 

 can be differentiated from phosphate and carbonate. 



Gersh Method for Chloride and Phosphate-Carbonate 



SPECIAL REAGENTS 



Anhydrous Petroleum Ether freshly distilled over sodium {b.p. 



20-40°). 

 Dried Paraffin ( GriXhler, m.p. 50-52°). Just before use heat at 100° 



or more in vacuo for about 15 min. or until bubbling stops. 

 Silver Nitrate Reagent 1. To 60% silver nitrate solution add 



enough cone, phosphoric acid to prevent precipitation of high 



concentrations of phosphate, then saturate with silver chloride. 



Filter and add 2-3 drops distilled water to each 10 ml. before 



using. 

 Silver Nitrate Reagent 2. Saturate 60% silver nitrate solution with 



silver phosphate and silver chloride. Filter and add water before 



using as for reagent 1. Store both reagents in glass-stoppered 



brown bottles in the dark. 



PROCEDURE 



1-5. These steps are identical with those in Gersh method for 

 potassium (see page 14). 



6. Cover sections on one cover slip with reagent 1 and those on 

 another with reagent 2. 



7. Drain off liquid from both cover slips and replace with a 

 drop of pure glycerol in each case. 



8. Mount on clean slides with glycerol-covered sections down. 



9. Expose both slides simultaneously to carbon arc radiation at 

 such distance as to avoid warming . 



10. Examine microscopically at once by direct or dark-field il- 

 lumination. These preparations last only a short time. The highest 

 power to be used with the dark-field condenser is a 4 mm. high-dry 

 or 2 mm. oil immersion objective with a numerical aperture of 0.95. 



Result. The reduced silver appears yellow to brown with or with- 

 out black or brown particles when viewed with direct illumination. 



