(1) H-acid solution. - 1 %, with 5 % sodium carbonate. This solution is used to indicate the presence of easily coupling diazo compounds in the rim of spots on filter-paper. In place of H-acid, R-salt, β-naphthol, hydrocyanic acid, etc., may be used.

(2) Resorcinol solution. - 1 %, with 5 % sodium carbonate. This is used for detecting any diazo compound, even those which do not react with H-acid (e.g. Aminonaphthol sulphonic acid 1:2:4).

(3) Diazotized p-Nitraniline. - This reacts with phenols and with amines. It must be preserved in the dark and will give a yellow coloration with sodium carbonate alone after 1-2 days, so that care must be taken in its use. o-Chloraniline may be used equally well in place ofp-Nitraniline.

(4) Alkali sulphide solution. - For detecting heavy metals in solution such as Iron, Copper, Tin, etc.