16 января, 2016 
Pokraskin 1. H Acid Solution. 1 per cent in 5 per cent soda, is used to test for easily coupling diazo compounds in spot tests on filter paper. R salt, /З-naphthol, hydrocyanic acid, etc. can also be used for this purpose.
2. Resorcinol Solution. 1 per cent in 5 per cent soda is used to test for all diazo compounds including those which do not react with H acid.
3. Diazotized p-Nitroaniline, Reacts with all phenols and amines. It must be kept in the dark, and after 1 to 2 days it gives a yellow color with soda alone, so care is necessary in its use. Diazotized o-chloroaniline can be used equally satisfactorily.
4. Sulfone Reagent. This reagent is a 10 per cent solution of 4,4′- diaminodiphenylmethane-2,2′-sulfone in 2 N hydrochloric acid (see footnote on page 243). The solution becomes green in time and a dark colored precipitate forms, but the supematent solution remains usable for a long time. Nitrite gives an intense but unstable blue coloration; the reaction is not prevented by strong acids or by weak oxidizing agents such as ferric salts.
5. Alkali Sulfide Solution. Used to test for heavy metals in solution (iron, copper, tin, etc.).
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