.'368 M. Gay-Lussac on the Action 



acid, is that of tartaric acid. No intumescence occurs, the 

 mixture does not blacken, and what is very remarkable is, that 

 so small a quantity of hydrogen is disengaged, that it must be 

 supposed to be derived from a minute quantity of foreign vege- 

 table matter. When the hydrogen is to be collected, the ex- 

 periment must be made in a retort, to which a long glass tube 

 is to be adapted, and this is to be immersed beneath a stra- 

 tum of water in a little mercury, to prevent absorption. The 

 retort may be heated in an oil or mercurial bath, to about the 

 temperature of 20^^ Centig., which is quite sufficient to form 

 oxalic acid. 



Citric and mucic acid also produce much oxalic acid. I also 

 obtained some from succinic acid ; but benzoic acid resisted 

 the action of the potash and remained unaltered. Acetate of 

 potash heated with excess of potash, was converted into car- 

 bonate. I nevertheless obtained a little oxalate of lime when 

 I poured nitrate of lime into a solution of the residual mass, 

 after having saturated it with acetic acid ; but it is very pro- 

 bable that the oxalic acid was derived from a small quantity 

 of foreign vegetable matter. 



Expressed vegetable oil treated with great excess of potash 

 did not undergo fusion. I obtained only a very small quantity 

 of oxalic acid. 



Animal substances, such as silk, treated with potash, gave 

 oxalic acid, attended with the evolution of hydrogen. Uric 

 acid evolved ammonia during the operation. The remaining 

 mixture was very white. Dissolved in water and saturated with 

 nitric acid, it gave out hydrocyanic acid and much carbonic 

 acid ; nitrate of lime afterwards produced an abundant preci- 

 pitate of oxalate of lime in the solution. Gelatin gave a similar 

 result, but with indigo I did not perceive any oxalic acid. 

 Carbonate of potash being substituted for caustic, did not pro- 

 duce oxalic acid with tartar. Lime and starch did not form 

 any, but soda was advantageously substituted for potash. 



It results from these experiments, that a great number of 

 vegetable and animal substances, when treated with caustic 

 potash or soda, are converted into oxalic acid. It is to be ob- 

 served that the formation of this acid precedes that of carbonic 

 acid, precisely in the same circumstances as those ia which 

 sulphur and potash, for example, produce hyposulphurous 

 acid and sulphuric acid ; — thus a vegetable substance, when 

 moderately heated with potash will give oxalic acid, and when 

 more strongly heated, carbonic acid. 



As very different organic bodies thus produce oxalic acid, 

 other products are necessarily formed. Many vegetable bodies 



give 



