Solutions for Spot Tests on Filter Paper

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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