Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 196

[Footnote 144: 'Lancet,' March 4th and 11th, 1876.]

_Pur. & Tests._--1. It is entirely soluble in water and rectified spirit.--2. When strongly heated it is wholly dissipated, and, if kindled, burns with a bright flame, leaving a bulky charcoal.--3. Its solution is absolutely neutral to test-paper.--4. Concentrated sulphuric acid causes it to agglutinate into resin-like lumps, with the accession of an intense blood-red colour.--5. When its aqueous solution is mixed with some hydrochloric acid, or dilute sulphuric acid, and the mixture is boiled for a short time, the liquid suddenly becomes turbid, and deposits SALIRETIN, under the form of a granular crystalline precipitate. This is characteristic.--6. No reagent deposits salicin without decomposition. See SALICYLIC and SALICYLOUS ACIDS.

=SAL'ICYL.= C_{7}H_{4}O. A compound radical, forming the basis of the so-called SALICYL-COMPOUNDS, or SALICYL-SERIES. It is known only in combination. The volatile oil of meadow-sweet is a natural hydride of salicyl, a substance which, when artificially prepared, is better known under the name of SALICYLOUS ACID. (See _below_.)

=SALICYL'IC ACID.= H_{2}C_{7}H_{4}O_{3}. A peculiar volatile, crystallisable acid, discovered by Piria. It is obtained by fusing salicylous acid with solid hydrate of pota.s.sa in slight excess, until the mixture turns white and gas is disengaged, and treating a solution of the residuum with hydrochloric acid, in slight excess to separate the pota.s.sa; the salicylic acid separates in crystals, which are purified by solution in hot water. It may also be obtained from the oil of partridge-berry (_Gaultheria proc.u.mbens_), by acting on it with a strong and hot solution of pota.s.sa, and afterwards separating the acid as before. This oil is methylo-salicylic ether, or salicylate of methyl. In its general properties, salicylic acid closely resembles benzoic acid.

The greater part, if not the whole, of the salicylic acid of commerce is now obtained by a method invented by Professor Kolbe. This process, which consists in acting on sodium carbolate with carbonic acid, is thus described in the 'Archiv der Pharm.,' 3rd series, v, 445.[145] In a strong crude soda liquor of known strength is dissolved a sufficiency of previously melted crystals of carbolic acid to saturate the soda.

[Footnote 145: 'Pharm. Journal,' 3rd series, v, 421.]

The solution is then evaporated in an iron capsule, and by means of stirring brought to a dry powder. The sodium carbolate so obtained is gradually heated in a retort to a temperature of from 220 to 250 C., in a continuous current of dry carbonic anhydride.

The reaction is ended when at the above-mentioned temperature no more carbolic acid pa.s.ses over. It might have been expected that, the reaction going forward in this manner, a molecule of carbonic anhydride would have been introduced into the molecule of sodium carbonate, and thus a molecule of sodium salicylate be formed.

This, however, is not the case, only half the sodium carbolate being converted into salicylate. The reaction proceeds according to the following equation:--

2NaC_{6}H_{5}O + CO_{2} = Na_{2}C_{7}H_{4}O_{3} + HC_{6}H_{5}O.

The disodic salicylate is dissolved in water and decomposed by hydrochloric acid. Salicylic acid then separates in crystalline films and may be purified by recrystallisation out of its solution in hot water.

_Props._--Salicylic acid is a white solid which forms acicular crystals; it melts at from 155-156 C.; it dissolves in about 1800 parts of cold water, but is more soluble in boiling water as well as in alcohol and in ether. An aqueous solution of salicylic acid mixed with one of a ferric salt produces a deep violet colour.

Professor Kolbe surmised that from the const.i.tution of salicylic acid, as revealed by his synthetical process, that it would split up with heat into carbonic anhydrate and carbolic acid, and hence that it might be employed as an antiseptic and antiputrefactive agent. He quotes the following experiments as confirmatory of his views on this point:--Mustard meal, which, in a few minutes after being mixed with warm water, gave off a strong smell of mustard oil, formed with water a scentless mixture, when a little salicylic acid had been previously added. No fermentation was set up by yeast in a fermentation of grape sugar, to which salicylic acid had been added; whilst in a sugar solution already in fermentation the action stopped after the addition of some salicylic acid. The preservation influence of this acid upon fresh meat is also recorded.

The following, among other experiments, in their results, ill.u.s.trate the physiological action of salicylic acid:--

Solution of amygdalin mixed with emulsion of sweet almonds developed no smell of bitter almonds if some salicylic acid were added. Beer, to which salicylic acid, in the proportion of 1 to 1000, was added, was thereby prevented from being spoiled by fungoid growth.

Fresh pure cow's milk, mixed with 004 per cent. of salicylic acid, and allowed to stand in an open vessel at a temperature of 18 C., curdled thirty-six hours later than a similar quant.i.ty of milk standing by the side of it, but containing no salicylic acid. The milk remained of a good flavour, the small quant.i.ty of salicylic acid present not being perceptible to the palate.

Some fresh urine was divided into two portions, and placed in separate vessels, after some salicylic acid had been added to one portion.

The urine containing the acid was on the third day still clear and free from ammoniacal odour, whilst the other portion was far advanced in putrefaction.

Professor Thiersch has investigated the antiseptic action of this acid, specially in relation to surgery. He has found that as a powder, either alone or mixed with starch, it destroys for a long time the fetid odour of cancerous surfaces or uncleansed wounds, without setting up any inflammatory symptoms. A solution of one part of salicylic acid, and three parts of sodium phosphate in fifty parts of water, promotes the healing of granulated surfaces.

According to Dr Rudolph Wagner, salicylic acid may be applied to the following industrial purposes:--

If a concentrated aqueous solution of salicylic acid be applied to fresh meat, and the meat be then placed in well-closed vessels, it will remain perfectly fresh for a long period. This solution is also very useful in the manufacture of sausages and such food. b.u.t.ter containing a bitter salicylic acid will remain fresh for months, even in the hottest weather.

The same acid prevents the moulding of preserved fruits. In the manufacture of vinegar this acid is of great utility.

The addition of a little salicylic acid renders glue more tenacious. The acid also prevents decomposition in gut and parchment during their manufacture.

Skins to be used for making leather do not undergo decomposition if steeped in a dilute solution of salicylic acid.

Weaver's or bookbinder's glue and other allied substances may be preserved for a long period by treating them with a solution of this acid.

Alb.u.men may be preserved by the same means.

This acid is a very delicate test reagent for iron.

The methyl ether and amyl ether of salicylic acid are used as perfumes.

The calcium salt on keeping and distilling with water yields a liquid which has a strong odour of roses.

Mr Rother, an American chemist, contends that the antiseptic powers of salicylic acid have been much overrated. He states that he had tried it for the preservation of the syrups of marshmallow, raspberry juice, and milk, and that it was a failure. Professor Salkowsky regards it as of less value as an antiseptic than benzoic acid.

Dr Muter gives the following method for estimating the value of commercial samples of salicylic acid, and of detecting it in milk and similar organic solutions:--A standard solution of pure salicylic acid (1 grain of acid dissolved in 1 litre of water, so that 1 c.c. represents 1 mgm. of acid) is prepared; the _indicator_ solution consists of a solution of pure neutral ferric chloride, of such a strength that 1 c.c. added, drop by drop, to 50 c.c. of standard acid, just ceases to give any increase in intensity of colour; 1 gram of the commercial sample is then dissolved in 1 litre of water, and 50 c.c. is put into a Nessler tube; to this 1 c.c.

of ferric solution is added, and the colour observed after standing for five minutes, some of the standard acid is also poured into another tube, and made up to 50 c.c. with water, and the 1 c.c. of ferric chloride added. When the colours are alike the amount of pure acid present in the sample is equal to the amount of pure acid added. All mineral acids should be absent, even acetic acid affects the reaction. To detect the presence of salicylic acid added to beer or milk, four ounces of these liquids are dialysed for twelve hours in a pint of distilled water; if after that time salicylic acid is still found to be present, the dialysis must be continued for forty-eight hours. The amount present is determined in the manner above stated.

=SALICYL'OUS ACID.= C_{7}H_{6}O_{2}. _Syn._ SALICYLOL, HYDROSALICYLIC ACID, HYDRIDE OF SALICYL, ARTIFICIAL OIL OF MEADOW-SWEET. A nearly colourless, oily, inflammable liquid, discovered by Pagenstecher in the volatile oil of _Spiraea ulmaria_ (meadow-sweet), which, when pure, entirely consists of it; and by Piria, as a product of the decomposition of salicin.

_Prep._ The oil of meadow-sweet is mixed with a strong solution of caustic pota.s.sa, and the yellow crystalline ma.s.s which separates on agitation is purified by pressure between folds of bibulous paper and recrystallisation from alcohol; the resulting crystals (salicylite of pota.s.sium) are then decomposed by the addition of dilute sulphuric acid, the floating oil separated from the water, and freed from moisture by careful distillation from chloride of calcium.

_Prop., &c._ Salicylous acid is soluble in ether and alcohol, and slightly so in water, to which it imparts its peculiar fragrance and the characteristic property of striking a deep violet colour with the sesquisalts of iron. It is distinguished from salicylic acid, which also exhibits this reaction, by its liquid form and odour.

=SALI'VA.= See MASTICATION.

=SALM'ON.= _Syn._ SALMO, L. The _Salmo Salar_ (Linn.), a well-known, soft-finned abdominal fish. Its normal locality is at the mouth or estuary of the larger rivers of the northern seas, which, during the breeding season, it ascends, sooner or later, in the summer months, against all obstacles, for the purpose of depositing its sp.a.w.n.

The salmon is an excellent and highly esteemed fish; but it is rich, oily, and difficult of digestion, and, therefore, ill adapted to the delicate or dyspeptic. When pickled, salted, or smoked it is only fitted for persons of very strong stomachs, although in this state it is regarded as a great delicacy by epicures.

Salmon has the following composition:--

Nitrogenous matter 161 Fat 55 Saline matter 14 Water 77 ------- 1000

Salmon is preferably cooked by boiling. One weighing 10 lbs. will require to be gently simmered for about an hour, reckoning from the time the water commences boiling. For fish of other weights, from 6 to 7 minutes per lb.

may be allowed. See FISH, &c.

=SALOOP'.= Sa.s.safras (chips) tea, flavoured with milk and sugar. A wholesome and useful drink in cutaneous and rheumatic affections. See SALEP.

=SALT.= _Syn._ SAL, L.; SEL, Fr. Salts may be regarded as acids in which one or more atoms of hydrogen, a constant const.i.tuent of all true acids, are replaced by a metal or other basic radical. This relations.h.i.+p between acids and salts will be better understood by reference to the subjoined list of acids and their corresponding pota.s.sium and ammonium salts:--

Acids. Salts.

HCl (Hydrochloric acid) -- KCl (Chloride of pota.s.sium).

" " " -- NH_{4}Cl (Chloride of ammonium).

HNO_{3} (Nitric acid) -- KNO_{3} (Nitrate of pota.s.sium).

" " " -- NH_{4}NO_{3} (Nitrate of ammonium).

H_{2}SO_{4} (Sulphuric acid) -- K{2}SO_{4} (Sulphate of pota.s.sium).

" " " -- (NH_{4})_{2}SO_{4} (Sulphate of ammonium).

Acids are, in fact, hydrogen salts. The so-called DOUBLE SALTS are, according to one view, combinations of two salts of the same acid, but of different basic radicles; thus, common alum is a compound of sulphate of aluminum and sulphate of pota.s.sium.

The salts are a most important cla.s.s of bodies, and their applications and uses in the arts of life and civilisation are almost infinite. See NOMENCLATURE, &c.

=Salt of Bark.= See EXTRACT OF BARK, DRIED.