Manufacture of Picric Acid.

Practical Magazine 19, 1876

(Chemistry applied to the Arts, Manufactures, &c.
Acids, Alkalies, and Salts.)

The plant Xanthorrhæa arborata, indigenous to Australia, which has been known for about a century, produces a resin known in commerce under the name of "yellow Botany Bay resin." This resin appears likely to answer well for the manufacture of picric acid, not only on account of its low price, but also because it yields a good return. To ascertain this, Herr Wolfsleben procured some of the pure resin and experimented upon it. Ten grammes (6½ dwt.s.) of the resin, pulverized, were put in a drinking-glass with 50 grammes (1¾ oz.) of crude nitric acid of specific gravity 1'16. This glass was covered with a bell glass, and the mixture put in digestion at a moderate temperature. The mass soon swelled up, and on the surface of the liquid was formed a deep brown crust, which required to be every now and then broken, and submerged with a glass stick. When, after three hours, the disengagement of ruddy vapours was found to cease, it was allowed to cool. Next day the bottom of the glass was found covered with a layer of crystals of an intense yellow colour, above which was a compact resinous mass of a brown-red colour. This mass was removed and again digested in 25 grammes (16 dwts.) of nitric acid, but it was found that this acid had now scarcely any effect, and there was no longer any formation of nitrous acid. Nor was there any separation of crystals by cooling, so that it was considered superfluous, so far as concerns the preparation of picric acid, to treat the resinous mass a second time with the acid. However; as in the present case the object was to lose as little as possible of the product sought, after the crystals of the first liquor had been collected, the second liquor was added to the mother-liquor before evaporating. The evaporation was carried on to dryness, the first crystals were added, and the nitric acid which might still adhere to them was expelled at 212° Fah. The final residue weighed 6½ grammes (100 grains troy), i. e. nearly two-thirds of the resin first put in. It was composed of yellow crystals with nothing amorphous, and some isolated crystals of oxalic acid. After the picric acid thus obtained had been again crystallized, to free it from this oxalic acid, it was found to weigh 5 grammes (3¼ dwts.). The resin in question is therefore well adapted for the purpose intended


- Polytechnisches journal.

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