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properties have been fully described in our ori-ginal article, and the difference between thepure barytes obtained from the nitrat and thatprocured from the crystals of barytes formed bysolution in water, has been mentioned in thearticle Alkali in this appendix.

Peroxyd o f Barium . According to the ex-periments of Messrs. Gay Lussac and Thenard,barytes can absorb oxygen, anil thus produce anoxyd of barium of a higher state of oxydationthan barytes. 11 For this purpose some dry oxy-gen gas was passed into a glass tube over mer-cury, and along with it some fragments of purebarytes arising from the calcined nitrat On ap-plying the heat of a lamp, the oxygen was veryrapidly absorbed, and the barytes appeared as ifglazed on its surface, and became greyer.

The glass was then filled with hydrogen andheated as before. The hydrogen was absorbedin large quantity, and sparks were seen toproceed from the barytes. No water was va-porized, so that all of this fluid, which musthave been produced by this absorption of hy-drogen, was absorbed by the barytes, whichthen became very fusible.

The experiment was repeated with similarsuccess with barytes prepared by calcining thecarbonat of barytes with lamp-black in an in-tense heat; so that the effect could not havebeen produced in the first instance by any unde-composed nitric acid.

BENZOIN- Benzoic Acid. Benzoats .

We have to mention some additional facts re-lative to this resin and its products, which areamong the most interesting of this class of vege-table substances.*

When benzoin is gradually beated in mode-rately dilute nitric acid, it is dissolved into a fightyellow liquid, which on cooling gradually de-posits nearly the whole of the benzoic acid,whilst the resin appears to remain dissolved.This solution is totally decomposed by water.

Sulphuric acid dissolves benzoin into a deepred liquid, but carbonizes a portion of it. Thesolution gives a lilac precipitate with water.Acetic acid dissolves this resin even in the cold.When saturated by boiling, much benzoic acidseparates on cooling.

When these acids are added to the solutionof benzoin in alcohol, a precipitate is formed(with all but the nitric) which is probably a com-pound of the resin and acid, and an excess ofthe same acid generally redissolves a part of thisprecipitate. Nitric acid on the other hand does

k Recherches, tom. 1. p. 169. » Braude in Pliil

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not render the alcoholic solution turbid, but givesit a dark red colour, so that this acid seems tohave a greater solvent power over the resin ofbenzoin.

Jleuzoic Acid. Scarcely two thirds of thewhole acid contained in benzoin is procured bymere sublimation. Sclieele’s process (mention-ed in our original article) gives the purest acid.

Some German chemists have also employedcarbonat of potash or soda, as an intermede forobtaining this acid. Benzoin, boiled repeatedlywith about a tenth of its weight of carbonat ofsoda and sufficient water, the resin being takenout two or three times and triturated, and againboiled with the same liquor, yields at last nearlythe whole of its acid to the soda, and the solu-tion of benzoat of soda deposits its acid onadding the sulphuric acid.

Benzoic acid is soluble in most of the acids,but separable from them by dilution with water.

A singular fluid compound of benzoic acidand camphor is mentioned by Mr. Gowar,' 1 to beproduced by adding a definite quantity of waterto a solution of both these substances in alcohol.

Twenty grains of benzoic acid and as muchcamphor dissolved in half an ounce of commonalcohol, and then diluted with as much water,gradually separates into two liquids, both ofwhich are quite transparent if the acid is freefrom resin, but yellowish if otherwise.

Both the upper and lower liquids appear to hacompounds of alcohol, water, benzoic acid andcamphor. The lower, which has an oily appear-ance, is strongly acid and aromatic, and by eva-poration forms crystals apparently composed ofbenzoic acid and camphor. Cold water added tothis liquid immediately decomposes it, the ben-zoic acid being precipitated in the form of shiningcrystals, and the camphor floating on the top.The upper fluidonstandingfora time, sometimesdeposits large crystals floating upon the lowerstratum, which are chiefly benzoic acid, butaltered from its usual crystallized form, probablyby the presence of some camphor.

It requires pretty exactly the above mentionedproportion of benzoic acid, camphor, alcoholand water, to produce this singular separationinto two distinct solutions, for when more ofthe spirituous menstruum is used, the whole re-mains as one uniform solution, and when, agreater proportion of water is employed, muchof the camphor and part of the acid separate.

Mr. Bucholz has examined some of the lead-ing properties of the benzoic acid, with a view

Journ. vol. x. ‘ Phil. Journ. vol. xxviii. p. 28.

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