128 Notice of some Recent [Feb. 



The liquid obtained is introduced into a glass retort, and 

 distilled till it acquires the consistence of syrup ; the 

 receiver is then changed, and the distillation carried to 

 dryness. The last liquid which comes over is exposed to a 

 severe cold, or to spontaneous evaporation in vacuo. Yellow 

 crystals separate, which are pressed between blotting paper 

 and again re-dissolved in water. On cooling, crystals of 

 pure pyrotartaric acid are deposited. An analysis of this 

 acid afforded Carbon .... 52*11 



Hydrogen . . . 5*30 

 Oxygen . . . . 42*59 



100*00 

 This acid is white, destitute of smell, very soluble in 

 water and alcohol, with a taste resembling tartaric acid. 

 It melts at 212, and boils at 370°. Acetate of lead precipi- 

 tates it ; the white product is insoluble in water, but very 

 soluble in an excess of acetate. Pyrotartrate of potash, 

 when poured into a solution of the proto-nitrate of mercury, 

 produces a copious white precipitate, and forms with per- 

 sulphate of iron a yellow precipitate, soluble in twice its 

 weight of water ; with sulphate of copper a green product 

 which requires nearly the same quantity of water to 

 dissolve it. 



Pure benzoic acid may be procured, according to Righini, 

 by dissolving the acid in four or five times its weight of 

 sulphuric acid diluted with six parts of water, adding 

 during the ebullition, a small portion of animal charcoal, 

 and filtering. On cooling the acid separates in crystals. 

 This process may be repeated if the crystals are not pro- 

 perly formed, and there is any smell. To obtain the cry- 

 stals in perfect purity, they may be dissolved in alcohol, 

 and the solution exposed in a subliming apparatus on the 

 sand-bath, the heat being applied in such a manner that 

 the alcohol alone is volatilized. The acid is thus obtained 

 in long needles, perfectly white and destitute of smell. 

 (Ann. de Chim. lvi. 444.) 



Sulphobenzoic Acid. — This acid is formed by adding 

 benzoin to sulphuric acid as long as any of it is taken up, 

 allowing the flask to cool occasionally during the decom- 

 position. (Poggendorff, xxxi.) By dissolving the acid in 



