OBSERVATIONS ON BENZOIN. 87 



. The greateft quantity of benzoic acid is obtained by Chap- Chaptal's me- 

 tals method, which conlifts in diftilling all the piodu#s over i, e ° z ^c ° c^d.""^ 

 together, and feparating the acid by means of boiling water. 



The acid, however, thus obtained, is by no means fo pure Scheele's pro- 

 as that procured by Scheele's procefs *, which is certainly far ccfs ' 

 preferable in many refpects. 



.Another way of obtaining the benzoic acid, is that recom- Gottling's pro- 

 rae, led by Gottling. It eonfifh in cligefiing the balfam, in a cefs , for obtain - 



J « & to ■ jn g benzoic 



gentle heat with carbonate of potafh and precipitation by ful- acid. 



phuric acid. Gren made ufe of carbonate of foda: but it mud Gren's procefs. 



be obferved that in both thefe proceffes, the acid is by no 



means fo pure as that obtained by Scheele's method, becau/e 



a far larger proportion of the benzoin itfelf is foluble in the 



fixed alcalies, than in lime water, (the latter only diffolving a 



very fmall portion, to which its brown colour is owing) and 



• Scheele's procefs is as follows : " Upon four parts of unflacked 

 lime pour 12 parts of water, and after the ebullition is over add 96 

 parts more of water j then put 12 parts of finely powdeied benzoin 

 info a tin pan ; pour upon it firft about fix parts of the above milk 

 ot lime, mix them well together, and thus fucceffively add the reft 

 of the mixture of lime and water. If it be poured in all at once, 

 the benzoin inftead of mixing with it, will coagulate and run to- 

 gether into a mafs. This mixture ought to be boiled over a gentle 

 fire for half an hour, with conftant agitation ; then take it from the 

 fire, let it ftand quiet for an hour, in order that it may fettle; pour 

 off the fupernatent limpid liquor into a glafs veflel. Upon the re- 

 mainder in the pans pour 96 parts of pure water, boil them toge- 

 ther for half an hour, then take it from the fire and let it fettle j 

 add the fupernatent liquor to the former; pour upon the refiduum 

 fome more water, boil it as aforefaid, and repeat the fame procefs 

 once more. At laft put all the reliduums upon a filter, and pour hot 

 water feveral times upon it. During this procefs, the calcareous 

 earth combines with the acid of benzoin, and feparates it from the 

 refinous particles of this fubftance. A fmall quantity of the refin 

 is difTolved by the lime water, whence it acquires a yellow colour. 

 All thefe clear leys and decoftions are to be mixed together and 

 boiled down to 24 parts, which are then to be ftrained into another 

 glafs veflel. After they are grown cold, muriatic acid is to be 

 added, with conftant flirting, till there be no further precipitation, 

 or till the mafs taftes a little fouriih. The benzoic acid which was 

 before held in folution by the lime, precipitates in the form of a fine 

 powder." Vide Thornton's Chemiftry, Vol. II. page 123. 



which 



