Chemical Science, 223 



ai^ain treated with carbonate of lime ; and now the precipate, when 

 collected on a filter, is to be well washed, pressed, and a third time 

 decomposed by sulphuric acid. The clear liquor now obtained is 

 to be boiled with animal charcoal, filtered, and evaporated. When 

 sufficiently concentrated, it must be allowed to deposit, and the 

 fluid, when poured off, be put into stoves heated to between 68° and 

 77° Fahr. Crude crystals of the citric acid will be thus obtained ; they 

 are to be drained slightly, washed, and recrystallized. — Jour, de 

 Phar.—Phil. Mag. M.S., iv. 153. 



41. Nature ofAloetic Acid, or the Bitter of Aloes. — M. Liebeg 

 finds this substance to be a combination of carbazotic acid, and a 

 particular substance having many of the properties of resins. The 

 bitter of aloes may be formed in large quantity, by acting upon 

 aloes with nitric acid of the specific gravity of 1.25. The substance 

 obtained forms a purple salt with potash, but little soluble, and pre- 

 cipitating the salts of baryta, lead, and peroxide of iron, of a deep 

 purple colour. When a solution of this salt was precipitated by 

 acetate of lead, the water employed to wash the precipitate had a 

 yellow colour, and deposited small crystals of the same colour. These 

 crystals heated in water with sulphate of potash, gave carbazotate of 

 potash, and from that carbazotic acid was obtained. 



When aloes are heated with nitric acid of specific gravity 1.432, 

 until the liberation of nitrous vapour ceases, and the liquid be mixed 

 with a little water to separate a small quantity of bitter principle, 

 then by neutralization with potash and evaporation, a large quantity 

 of carbazotate of potash in fine crystals is obtained. 



Wool, morphia, narcotine, and myrrh, did not give carbazotic acid 

 by treatment with nitric acid. — Ann. de Chiniie, xxxvii. 171. 



42. Preparation of Gallic Acid. — ^The following is M. Le 

 Roger's method. Gall-nuts are to be exhausted by repeated decoc- 

 tions, the liquid obtained concentrated and precipitated by a solution 

 of jelly ; the tannin thus rendered insoluble is to be filtered out ; very 

 pure animal charcoal is to be added to the liquid, and boiled with it 

 for eight or ten minutes and the whole filtered, when the liquid, on 

 cooling, will give pure white and silky crystals of gallic acid, 

 amounting, when the best galls are used, to one-fourth of their 

 weight. — Mem. de Geneve. 



o» 



43. Volatilization of Alcohol. — According to M. Soemmering 

 strong alcohol yields a weaker spirit at the commencement of 

 distillation than it does afterwards. With weak alcohol, the weaker 

 it is the more readily is its strength increased by distillation ; on the- 

 contrary, the more concentrated it is, the more difficult is it to remove 

 the rest of the water. When alcohol of specific gravity 0,796 is dis- 

 tilled, the weakest comes over first, and the product becomes 

 stronger as the operation proceeds. — Bull, Univ. A. ix. 344. 



