Resorcinum

Changes of colour in solutions of this substance are common. The following are two good examples:

No. I. darkens in colour rapidly. This is owing to absorption of oxygen by the resorcin in presence of alkali. It behaves like hydroquinone and pyrogallol in this respect. No. II. becomes quite red, and stains skin and hair a carroty red. This combination is more common as a lotion, and is referred to later.

Sodii Salicylas

The following are examples from practice of changes referred to on pages 71 and 72 :

Becomes almost black. Dissolve the bicarbonate in 6 ounces of aerated water, add the morphine dissolved in 1 ounce, and finally the salicylate.

As bad as No. I., being deep orange in a few hours, and finally black. Prescribers say it is good therapeutically, the ammonia counteracting the heart-depression which the salicylate causes.

This becomes almost black after standing a week or two, and a pleasant odour is developed. The latter is probably due to the formation of ethyl salicylate, and the colour to di-or tri-nitro-salicylic acid.

Becomes red owing to the action of nitrous acid from the spirit of nitre upon the sodio-theobromine salicylate.