1818.] M. Vauquelin on Sorbic Acid. 295 



for want of a sufficient quantity of fluid to dissolve it, is partially 

 melted, is at first kept on the surface by the force of ebullition, 

 but after some time falls to the bottom, and as it cools becomes 

 strongly fixed to the vessel. As the solution of the sorbate of 

 lead is slightly acid, Mr. Donovan supposed that there was both 

 a super-sorbate and a sub-sorbate ; but in this he was mistaken ; 

 for by treating the supposed sub-sorbate with a fresh quantity of 

 water, it is all dissolved, and reduced to the same state. The 

 sorbate of lead contains 12*5 per cent of water; when it is dried, 

 it is composed per cent, of 



Sorbic acid 33 



Oxide of lead 67 



100 



M. Vauquelin used every means to detect malic acid in the 

 juice of the sorb, but without effect ; he was, therefore, led to 

 suppose that what Mr. Donovan had taken for the malate of lead 

 was a mixture of phosphate of lead and a colouring matter, 

 united to the oxide of lead. 



The method which Mr. Donovan has pointed out for procuring 

 the sorbic acid appears a veiy correct one. It consists in par- 

 tially decomposing the sorbate of lead by sulphuric acid, and in 

 passing through the fluid a current of sulphuretted hydrogen. 

 The fluid is then filtered and concentrated. M. Vauquelin 

 observes, that in order to obtain this acid colourless and very 

 pure, it is necessary to employ sorbate of lead that has under- 

 gone several successive crystallizations, as it contains a colouring 

 matter and a portion of phosphoric acid. 



When the sorbic acid is evaporated to the consistence of a 

 syrup, it forms mammilated masses of a crystalline structure ; it 

 still contains a considerable quantity of water, and deliquesces 

 when exposed to a moist atmosphere. Lime water and barytic 

 water are not precipitated by the sorbic acid when in solution, 

 although the sorbate of lime is only slightly soluble. One of the 

 most characteristic properties of the sorbic acid is the precipitate 

 which it gives with the acetate of lead, which is at first white 

 and flocculent, but afterwards assumes a crystalline appearance. 

 Potash forms a deliquescent salt with the sorbic acid ; barytes 

 forms with it a salt which is more crystallizable, but the form of 

 which it is not easy to ascertain. The salt deprived of water 

 consists of 



Sorbic acid 47 



Barytes 53 



100 



The sorbic acid is with difficulty saturated by the oxide of 

 copper even when warm ; the sorbate of copper does not crystal- 

 lize ; dried in a capsule it leaves a varnish of a beautiful green 



