of a newly -discovered vegetable Add. 441 



Sorbic acid, when perfectly pure, is a transparent, colourless, 

 and inodorous fluid, soluble in alcohol, and in any proportion of 

 water. When evaporated, it forms an uncrystallizable sohd 

 mass which deliquesces: when subjected to distillation, the li- 

 quor which passes over shows no traces of acidity. Its acidity 

 is such that it causes even a painful sensation on the organs of 

 taste. It is not much altered by being kept in an uncombined 

 state. I have had it for more than a year in a corked phial, 

 and at the end of that time no other change was produced than 

 the separation of a tenuous coagulum, small in quantity, as the 

 acid was very pure, but it is more abundant when the acid is 

 impure. When mixed with malic acid, as in fruits, this acid is 

 the first to disappear, while the other retains its properties long 

 after the commencement of decay in the plant. 



A quantity of malate of lead obtained from SemperviimmTec- 

 toTum was boiled with sorbic acid and a little water ; the whole 

 from being colourless became somewhat brown. The liquor 

 was then filtered, and the turbid liquor which came through 

 was heated until it became clear ; it was then suffered to rest. 

 As it cooled, it let fall a powder ; but when this was filtered off 

 the liquor remained clear, and in an hour a great profusion of 

 crystals was let fall. The mass which remained on the filter 

 contained some gritty particles. 



Thus it is evident that malate of lead was decomposed by 

 sorbic acid, which could not happen unless the latter were a 

 distinct substance. Tlie malate v/as ouly partly decomposed, 

 the oxide of lead united to the excess of sorbic acid forming 

 supcr-sorbate of lead, while the disengaged malic acid dissolved 

 as much as it could of the remaining undecomposed malate, 

 forming super-malate of lead. The brown colour was produced 

 by disengaged malic acid. The super-malate, as it cooled, de- 

 posited its malate in the state of powder, and the super-sorbate 

 soon after deposited sorbate of lead in the state of crystals; and 

 the original mass was found to contain gritty particles of sub- 

 sorbate. 



In the same manner, when a precipitate obtained by acetate 

 of lead from the juice of the Sorbus berries is washed with 

 boiling v/ater, scarcely any nialate of lead is deposited ; and if 

 the fluid contain much free sorbic acid, the iridescent |)ellicle, 

 which is a characteristic of malate of lead, does not appiar. 



I shall now proceed to the combinations of this acid, so as to 

 distinguish it from malic acid : and first the salts which it forms 

 with lead should be briefly recapitulated. 



The sub-sorbate is insolulile in water ; if in a mass, it ii 

 dense and hard : if in powder, it is gritty. 



The neutral eorbatc, if obtahied by precipitation, is a wliite 



powder. 



