Salicin (C,„H„0„) is a neutral bitter principle contained in the bark of the various species of willow and poplar (sallow, osier, aspen, &c.). It readily crystallises out from a concentrated decoction of the bark, after tannic acid amid colouring matter have been removed by hydrated oxide of lead.
When pure, salicin occurs in white silky crystals, soluble in water or in alcohol, but insoluble in ether or oil of turpentine. It melts at 248' Fahr., loses water at 392' Fahr., and at a higher temperature decomposes. Concentrated sulphuric acid communicates a blood red colour to it ; the liquid, neutralised with chalk, yields a deliquescent chestnut-brown powder, containing, according to Mulder, am(phorefic arid. Water decomposes the red body formed by sulphuric acid; heat, also, gives rise to the formation of a resinoid body, that has been called by one chemist olirin, by onother main, while a third thinks it to be saliretin. Several chlorine derivatives of salicin exist.
Saligenin (C„I1,0,) and grape sugar result from the action of boiling dilute acids upon salicin Hence salicin is one of the glucosides. Saligenin crystallises in colourless crystals, very soluble in boiling water, alcohol, or ether. It is partially volatile; most oxidising agents convert it into hydride of salicyl, while chlorine gives rise to trichlorophenic acid.
Saliretin is a product of the action of heat upon saligenin in closed vessels; it is also produced by prolonged ebullition of saligenin with dilute acids. It is a white or yellow-coloured resinoid body, insoluble in water or in ammonia, but soluble in alcohol, ether, or concentrated acetic acid.
Helicin (2 + 3aq.) is obtained on digesting salicin in ten times its weight of nitric acid of specific gravity P160 for about a day : hydrogen is thus removed from the salicin, water being formed, and helicin deposited in acicular crystals. It is inodorous, of slightly bitter taste, very soluble in boiling water or alcohol, but almost insoluble in ether. Chlorine and bromine act upon, and give rise to derivatives of, helicin.
Helicoidin (C„H„0„ + 3aq.) seems to be a combination of helicin and ealicin (C„I1„0„ = C,„H„0„ + It is produced when the oxidation of salicin by nitric acid is incomplete, or when the specific gravity of the acid is less than that above indicated.
Populin + 4 aq.), or salicin in which an equiva lent of hydrogen is replaced by benzoyl, has already been described.
[Poput.m.] Coumarin, a fragrant principle of several plants, seems to be allied to the members of the salicylic group, inasmuch as it yields salicylate of potash when fused with the hydrae of that base. It is further described in a separate article. [Coma/oils.] Salicylic add (HO,C„H,0,). In combination with methyl this acid exists naturally in oil of wintergreen. [ESSENTIAL Otis.] On boiling the oil for a few minutes with solution of potash, neutralising by hydrochloric acid, and allowing the mixture to cool gradually, salicylic acid crystallises out in acicular tufts. Salicylic acid may also
be formed by projecting salicin, in small portions at a time, into hydrate of potash fused in a silver basin, the temperature not being allowed to rise higher than 750' Fahr. On dissolving the mass in water and adding hydrochloric acid, the salicylic acid is precipitated, and may be purified by recrystallieation from boiling water.
Salicylic acid fume at 310 Fahr., and at a higher temperature !sublimes unchanged. It is soluble in alcohol, ether, or oil of turpen tine. A mixture of peroxide of manganese and sulphuric acid oxidises it to formic acid. By ebullition with nitric acid it is converted first into nitrosnlicylic acid and, finally, into picric acid. Distilled with excess of lime it is split up into carbonic and phenic acids. Its solutions give an inky-blue precipitate with permits of iron, the colour disap pearing on the addition of hydrochloric acid.
Salicylic acid decomposes carbonates with effervescence, and forms salicylates that are, for the most part, monobasic and crystalline. The potash salt contains (KO,C,,H,0,, aq.) ; the double salicylate of copper and potash ham the formula KO,C„{ Cu0, + 4aq. : it crystallises in beautiful emerald green plates.
Salicylic ethers.—Although the oil of wintergreen appears to be a definite salicylate of methyl (C,I1,0,C„11,0,), it nevertheless plays the put of an acid, and from its source has been termed Gaultheric acid : it still admits of the replacement of an equivalent of hydrogen by a metal or a radical, gaultherates being formed ; thus :— Nitrosolicylie arid (C„IIANO,h0„ + 261.1, tidied also indiyotic and and &odic Kid, has already been described (ANuse Am]. Binitro salicylic acid, or sieropopaddc acid, contains .4aAydrois salicylic acid, or salicylic enAydride (e„11.0,, C,.H,P,), is formed by the action of oxychloride of phoepliorus on dry salieylate of soda. It is a gummy or oleaginous-looking body, soluble in alcohol. It is converted into ordinary salicylic acid by boiling with solution of Salleylide tC„I1,0,1 is a white. amorphous, pulvenilent substance, formed in the preparation of salicylic anhydride. It is insoluble In ether, fuel almost insoluble in alcohol.
Sant,' lark acid Is found in the urine, after salicylic acid has bean taken Into the stomach. Boiled with hydrochloric acid it splits up into ealievlic acid and LYCOCOLL.
Chloride of salicy) (C,.11,0„,C1) is a fuming liquid, obtained on acting upon oil of inoulowaweet by perchloride of phosphorus.
Se/ire/amide (C„II,N0.1 results from the action of a strung solu tion of ammonia on the oil of wintergreen. It is a volatile solid, of yellow colour, soluble in boiling water, alcohol, or ether. By the action of the chlorides of benzoyl or cumyl upon salicylamide the following compounds are generated :—