Chemical Science, 191 



is decomposed by the alkali, and the oxalic acid set free. There 

 are many points of resemblance between the pectic and oxalic acids, 

 especially in the insolubility of their salts ; but, of course, the latter 

 opinion must remain in doubt until the gelatinous matter has been 

 separated, and pectic acid formed by its union with oxalic acid. 



If the acid properties of pectic acid are due to oxalic acid, then 

 the latter must exist in the carrot, combined with some base, and 

 the presence of the organic matter, with which it forms pectic acid, 

 must favour its separation by means of an alkali. This opinion 

 appears probable, if we consider that the bi- carbonates, which have 

 but a feeble alkaline action, disengage the pectic acid more readily 

 than a caustic alkali ; and also remark, that lime is found in the 

 expressed juice. It may be admitted, also, that an alkaline force, 

 however feeble it may be, is sufficient to develope pectic acid in the 

 expressed carrot, by means of water and heat. — Ann. de Chimie, 

 xli. 46. 



30. Glaucic Acid. — This substance, discovered by Dr. Runge, 

 and considered by him to be a new vegetable acid, occurs in several 

 species of the Dipsacus and Scabiosa, and is said to be obtained 

 thus. The roots of the devil's bit, or Scabiosa snccisa, are to be 

 dried, pulverized, digested in alcohol, and then ether added to the 

 solution ; white flocculi. precipitate, which are to be dissolved in 

 water, precipitated by acetate of lead, and the precipitate decom- 

 posed in water by sulphuretted hydrogen ; by evaporation of the 

 liquid, acetic acid is driven off, and glaucic acid remains. When 

 dry, it is a brittle yellow mass, which reddens litmus, neutralizes 

 ammonia, the neutral solution being at first yellow, but becoming 

 bluish green upon exposure to air, in consequence of oxidation of 

 the acid. — Brands s Archives, xxvii. 312. 



31. On the Formation of Acids in Vegetables, by M. Vauquelin. — 

 I have thought that, in a great number of cases, the developement 

 of acids in vegetables was principally occasioned by the presence 

 of alkalies. We find, in fact, the acids almost always neutralized 

 altogether, or in part, by various alkalies, as lime, potash, soda, 

 magnesia, and sometimes by vegeto-alkalies*; and I do not know 

 that the latter have ever been found in a free state in the vegetable 

 kingdom. 



The alkali which plays the greatest part in this respect is cer- 

 tainly lime, for it is most generally diffused, is most abundant at 

 the surface of the earth, and powerfully attracts acids. It does not, 

 certainly, enter into the organic kingdom in the state of lime, but 

 as carbonate, which, without exerting any deleterious action on 

 vegetables, still retains sufficient alkaline force to determine the 

 formation of acids, and particularly the oxalic, which it prefers to 

 all others. 



We may thus, as I have said elsewhere, explain the effect of 



