1818.] M. Braconnot on Sorbic Acid. 291 



of soda is thus procured, which is soiled by a red colouring 

 matter, to remove which it must be warmed for some minutes 

 with lime water, or cream of lime, which will remove the colour- 

 ing matter, and leave the sorbate of soda untouched. The 

 liquor must then be filtered, and will be found to be limpid and 

 colourless ; pass through it a current of carbonic acid gas to 

 separate the lime which it may contain ; the sub-acetate of lead 

 is then to be added, which will form a very white precipitate of 

 the sorbate of lead, from which, after having well washed it, 

 the- sorbic acid must be disengaged by diluted sulphuric acid 

 assisted by heat. By this process, M. Braconnot informs us 

 that the sorbic acid may be obtained in a perfectly pure state ; 

 it is uncrystallizable, and attracts moisture.* 



With respect to the characters of the sorbates, M. Braconnot 

 observes, that the tartrates are the vegetable salts which bear 

 the strongest analogy to them ; from their property of combining 

 with an excess of acid which, in most cases, diminishes their 

 solubility. But as the two acids differ in their power of crystal- 

 lizing, we may lay it down as a general principle, that when the 

 tartaric acid forms a salt that is only slightly soluble with any 

 base, the sorbic acid will form a crystallizable salt with the same 

 base ; and whenever a tartrate shall be uncrystallizable, by a still 

 stronger reason the sorbate of the same base will be so likewise. 



In the formation of the sorbates, 100 parts of sorbic acid 

 saturate a quantity of base which contains about 11 parts of 

 oxygen. Tartaric acid has a greater capacity for saturation; 

 according to Berzelius it is 1 1*94, while he estimates that of 

 citric acid at 13*588, that of acetic acid at 15-43, and that of 

 oxalic acid at 22-062. Ths sub-sorbates contain a quantity of 

 acid, double of that which is contained in the neutral sorbates. 

 All the sorbates swell up by heat, and generally are disposed to 

 attach themselves to the vessels in which they crystallize. The 

 sorbates of potash, soda, and ammonia, are uncrystallizable and 

 very soluble. M. Braconnot formed a neutral sorbate of lime, 

 by pouring muriate of lime into the solution of sorbate of soda; 

 it was in the form of transparent, granulated crystals, which are 

 not affected by the air, and contain no water of crystallization. 

 It requires for its solution 147 parts of water, at the temperature 

 of 53-5° Fahr. ; and less than 65 parts of boiling water. It is 

 composed of 



Sorbic acid 72 100-00 



Lime 28 38-89 



Toot 



We have it not in our power to decide upon the respective merits of the pro- 

 cesses of Mr. Donovan and M. Braconnot; but we may observe that Mr. Donovan's 

 succeeded in the hands of M. Vauquelin.— Eo. 



+ This differs a little from Vauquelin's estimate.— Ed. 



t2 



