BEN 



Benzoic Add, w'licli is of fufilcient importance to require 

 being dcfcribed more at large. If benzoin is rjeiitly heated a 

 Lttle above the degree of boiling water, it melis into an adhe- 

 five mafs, and at the fame time fends out a very copious, 

 denfo, white fume, of an extremely fragrant, diffulive, pene- 

 trating fmell, and fo acrid as irrefiftibly to excite coughing 

 and tears in thofe who are in any degree expofed to it. Th.is 

 fume foon condenfts on the firft cool body, and then appears 

 in the form of very beautiful fpicular cryftals, which gra- 

 dually colIe£l into a bulky feathery mafs, extremely light, 

 and of remarkable elegance and luftre. This cryiialline ii;afs 

 is the benzoic acid, a-id its acid property is prowd bv red- 

 dening litmus, neutralizing alkalies, and forming with 

 them peculiar falts ; in modei-n chemical nomenclature Cdlitd 

 JBenzoats. After the greater part of the acid has rifen by 

 fublimation, or before it, if the heat be at all increafed, a 

 thin yellowifh oil rifcs fliglitly tmpvreumatic, but ftrongly 

 imbued with the fragrance of the refui. On further heating, 

 an acidulous liquor comes over, together with a thick buty- 

 raceous matter; ftill, however, containing fome of thecrvllal- 

 lizable acid, which is not totally expelled till the end of the 

 procefs. 



This acid is readily foluble in alcohol, and in hot frate"-, 

 but fo fparingly in cold water, that a hot faturated folution 

 will depofit in crvilals almoft its faline contents by cooling. 



Several methods have been devifed for obtaining the ben- 

 zoic acid. The oldeft and moft expeditious is by fimple 

 fublimation. To perform any quantities of it, put ben- 

 zoin in an earthen pipkin ; apply to the veffcl a large cone of 

 clean white paper, palled down to the edges of the pot, and 

 fet it over an extremely flow charcoal, or other fire, juft fuf- 

 ficient to melt the benzoin. The acid will rile and cryftallize 

 upon the infide of the paper cone. However, as in tliis me- 

 thod the vapour has hardly room to ooncrcte, inftead of the 

 paper cone, another vefiel inverted over th^t which contains 

 the refin, and with a fmall hole drilled through its b.-.ttom, 

 maybe fubftituted; and when full, it may be gently (haken, 

 to detach the acid, and again apphed. From nine to twelve 

 drachms may be thus obtained from fixteen ounces of benzoin. 

 The remaining refin is ftill very aromatic, and fliould not be 

 loft. 

 ^ ■ Another method has been recommended by Scheele, who 

 in his excellent praftical obfervations upon this fait, has 

 treated it with that precifion and ingenuity which fo emi- 

 nently diftinguilh this chemift in every fubjeft, of greater or 

 lefs importance and difficulty, which he has illullrated by his 

 labours. 



He obferves, that befides fublimation, the acid may be ex- 

 trafted by lixiviation, and with the advantage of obtaining 

 it free from any admixture ot oil, which is apt to impair its 

 vhitenefs and luftre. If benzoin is boiled with water, and 

 the folution ftraiued while hot, and fufiered to cool, moft of 

 the acid taken up by the hot water depofits when cold, and 

 may then be collected pure. This method, iiowever, is im- 

 perfect ; for as the water does notmix with and divide the gum, 

 this lad foon foftens, and finks down, clofcly adhering to the 

 bottomof the veffei, and does not allow of the water eaCly to 

 penetrate it. Hence the folution takes place only at the fur- 

 face of the benzoin. 



The fame chemiil boiled powdered chalk and benzoin in 

 water, and filtrated the liquor. No cryftals were now depo- 

 fited on cooling, for the scid had diiTolved part of the chalk 

 into a bcnzoat of lime, which, being ver)' foluMe, remained in 

 the liquor. But on adding fome drops of vitriolic acid, the 

 benzoic acid was again feparated from the lime, and fell to 

 the bottom in a powdery form. Subllituting alkali for the 

 chalk, the fame tifeci took place, and the betjzoic acid, as 



BEN 



before, was precipiluted by the vitriolic. Cut this methofl 

 was ftill attended with the inconvenience of the benzoin con- 

 creting together, which floated on the furface during tlie 

 boiling. But on fubftituting quick lime this iuconveuieace 

 was avoided ; and it is tlierelore in tiie following method that 

 the benzoic acid may be procured the moft copicufly and the 

 pureft. Upon four ounces of unflacked hnie pour t'.relvc 

 ounces of water, and after the ebullition is over, add fis 

 pounds more of water; then put a pound of benzoin, liiiely 

 powdered, into a tin pan; pour on it at firft about fix ounces of 

 the above lime water; mix them well together, and then fuc- 

 ccillvtly the reft of the lime water. By this method the 

 refin will lie prevented from running together into one mafa. 

 Boil the mixture for half an hour, with conftant ftirrirg, then 

 let !t ftand, and pour off the clear liquor. On the remainder 

 in the pan, pour more lima water, and proceed as before, 

 adding the clear liquor to that firft obtained, and aifo filter 

 the rcfidue, to exhauft the liquor, which is now a weak folu- 

 tion of benzoic acid, with the lime of the hme water. Boil 

 down this liquor (which is of a light yellow) to two pounds, 

 and ftrain. WTien cold, add to the liquor muriatic acid gra- 

 dually, which will produce a white crj ftalline depofition, and 

 continue to add the acid till the liquor is fuperfaturated, and 

 taftes lourifh. The ftrongcr acid thus unites with the hme, 

 and the benzoic acid, now free, being of itfelf fcarccly foluble 

 in cold water, falls down as a white coagulum, which fliould 

 be waftied with miore cold water, and genth- dried. To give 

 it a cry ftaliine appearance, diffblve it in boiling water, filter it 

 through a cloth, and by cooling it will feparate in the form 

 of fpicular cryftals, but with fome lofs of the acid. 



The above proctfs of Scheele's m.ay however be a little 

 (liortened, it the lime in fubftance be mixed with the lime 

 water, previous to the addition of the benzoin ; for by this 

 method the folution may be at once made more concentrated, 

 and lefs of the liquid will fuffice, fo that much of the eva- 

 poration will be laved. Any of the ilronger acids will dif- 

 piace the benzoic irom lime, but the muriatic is the moll 

 convenient. 



Scheele obtained from 12 to 14 drachms of the concrete 

 acid from a pound of benzoin by this procefs. 



The benzoic acid, when pure, is quite white; for if yellow, 

 it is mixed with a Imall portion of the oil of the refin. 

 Though cryftallized, it is confidtrably clafljc, and difficult to 

 be reduced to powder. Its tafte is ftiarp, pungent, and 

 acidulous. It reddens tinfture of litmus. Wlien cold, it is 

 without fmell, but on applying heat it fends forth the pecu- 

 liar grateful odour by which it is charaftenzed. Heated by 

 itfelf, it chiefly fublimes, but a part is decompofed, giving an 

 acid phlegm, much oil, and carburetted hydrogen gas. It il 

 not alterable in the air, and does not evaporate by keeping 

 in a moderate temperature. Cold water diffolves only about 

 -J.I3 of its weight, but boiling water -J^^ ; and hence the co- 

 pious cryftallization from a hot water folution. It unites 

 readily to moft of the alkalies and earths fonning benzoats, 

 the properties of which have been but httle examined. 



The benzoat of lime is almoft the only C?It of this kind 

 found native. It is contained in the urine of fome animab, 

 particularly the herbivorous quadrupeds, and is aicertained 

 by adding to this fecretion fome muriatic acid, by which the 

 benzoic acid is made perceptible. 



Vv^ith potafli this acid forms a readily cryftallizable fait, 

 decompofable, like the reft of the benzoats, by a ftrongacid. 



Moft of the metaUic oxyds are diflblved by this acid, but 

 not the pure metals. 



Mr. Hermbftadt, in a feries of experiments on the aifWon of 



nitrous acid on the benzoic, found that the latter regularly 



alTuraed in tlte procefs a fmell like tHat of water didiliedover 



D d e bittar 



