Action of Heat on Citric Acid. 289 



tlirown down aftei* an addition of ammonia, as a gelatvpe of 

 difficult solution in water. From its boiling solution it cry- 

 stallizes in long, thin lustrous needles, loses nothing at 100°, 

 and burns with slight explosions; formula C' H^ O^ Aq.O. 

 From the liquid filtered from this salt are deposited on evapo- 

 ration crystals in six-sided columns, which at 100° lose one 

 atom of water. The citraconate of lead exists in four differ- 

 ent states. From an aqueous solution of the acid, to which 

 some ammonia has been added, acetate of lead throws down 

 a voluminous precipitate, which on being boiled is partially 

 dissolved, but the greater portion is converted into an inso- 

 luble crystalline powder = C' H+ O^ + Pb O. From the fil- 

 tered liquid crystallizes on cooling a non-crystalline powder 

 = C^ H+ O^ + Pb O + Aq. If the neutral salt of ammonia 

 be precipitated by the neutral acetate of lead a gelatinous pre- 

 cipitate is formed, which dried immediately becomes opake, 

 slightly yellow and gummy, = C* H* O^ + Pb O + 2 Aq. 

 Basic acetate of lead throws down from citraconatic salts 

 a white nearly insoluble crystalline powder = C' H^ O^ 

 + 2 Pb O. The citraconate of zinc, and of the protoxide of 

 mercury, are white and nearly insoluble. The neutral salt 

 of nickel green, the acid salt green, crystalline. The acid 

 salt of cobalt red, granular. The acid citraconate of the 

 protoxide of manganese forms an opake ductile mass. The 

 hydrate of the peroxide of iron is but slowly dissolved by 

 citraconic acid. 



Citric acid therefore presents four distinct periods of de- 

 composition : the first from the melting point to the evolution 

 of gas, during which water of crystallization (?) is given off". 

 The second period begins with the evolution of aceton and 

 carbonic oxide, and pyrocitric or aconitic acid is formed. 

 This is decomposed in the following period, under formation 

 of carbonic acid and pyraconitic or itaconic acid. In the 

 fourth period em})yreumatic oil is given off", and the residue 

 is carbonified. Three different acids therefore originate in 

 fixed order. The aconitic acid is probably tribasic, the ita- 

 conic and isomeric citraconic acids bibasic. 



Wackenroder has published in the Archiv tier Pharmacic 

 (xxiii. p. '26G-279) a series of experiments on the amount of 

 water of crystallized citric acid, from which he concludes that 

 the two kinds of citric acid hitherto admitted with four and 

 five atoms of water do not exist, or are never formed from 

 the usual citric acid under known conditions; that the cry- 

 stallized citric acid cannot exist with less than three atoms of 

 water; that the acjueous fluid which Crasso obtained by dry 

 distillation, and regarded as water of crystallization, is nothing 



Phil. Mag. S. 3. Vol. 18. No. U7. April 1811. U 



