3(X) CHEMICAL EXPERIMENT*. 



How to obtain It In order to obtain pure fluoric acid, one part of fluor fpaT 

 P urc * reduced to a fine powder, may be mixed with two of fulphu- 



ric acid, and one of water. The mixture is then to be intro- 

 duced into a glafs retort, to which a glafs receiver has been 

 previously luted, containing two ounces of water. Heat be* 

 ing then applied, the diftillation is to be carried on flowly. 

 After the decompofifion of the fluate of lime is effected, which 

 may be known by the difappearance of the whitifh vapours in 

 the retort, the contents of the receiver muft be filtered, and 

 diftilled water added to the filtered fluid, till, on a new ad- 

 mixture of water, no further cloudinefs appears. The acid 

 thus obtained contains no filex ; it is abfolutely pure ; and 

 may be kept in glafs bottles covered within with wax, or, in 

 preference, with a hard varnifli. 



17. Benzoic Acid exijis in Vanelloe* 



Cryftalline mat- A quantity of vanelloe pods [Epidendrum Vanilla, L.] which 

 ter on vanelloe. had ^^ kep( . wrap( . up j nto g bladder ^ and f urroun d e( | w j t h 



thin fheet lead for upwards of four years, were found to be 

 covered with a white powder of a pungent faline tafte. On 

 examining the internal parts of the wrinkled fhell of the pods, 

 the black feeds, when viewed under the magnifier, were 

 found to be covered over with a multitude of oblong cryftals, 

 crofling each other in all directions. 

 Experiments In order to examine thefe cryftals, one ounce of the pods 



benzoic add! C were Dro ^ en mto mia ^ pieced, and boiled in a Florence flafk, 

 with a quarter of an ounce of lime and fix ounces of diflilled 

 water, for about ten minutes. The whole mafs was then 

 fuffered to repofe, and the clear fluid, which was of an amber 

 colour, and aromatic bitter tafte, was (et afide. The refidue 

 was treated in a fimilar manner, and the fluid was added to 

 the firft. The clear folutions were then flowly evaporated to 

 one fourth. During this procefs a quantity of a brown adhe- 

 five fubftance feparated, which had all the properties of a true 

 refm ; its weight amounted to nine grains. On letting fall into 

 the concentrated folution, from which this refin had been fe- 

 parated, fome pure muriatic acid, the whole became turbid, 

 and a pulverulent yellow precipitate was depofited, which 

 increafed in quantity on heating the mixture. All the preci- 

 pitate obtained in this manner was then diffolved in diflilled 

 water, filtered, evaporated, and crvftallized ; it yielded beau- 

 tiful 



