ON VEGETABLE ACIDS 275 



till the earthy salt which does not contain nitrous acid be 

 saturated. Were the vinegar unaltered, it would distil off; 

 if it were converted into acid of sugar, it would not 'be 

 dislodged from the lime by nitrous acid. 



In like manner, distilled or Westendorfs vinegar should 

 be saturated with chalk ; the compound should be reduced 

 to crystals, and then exposed to as strong a fire as it can 

 bear without the expulsion of the acid, in order to separate 

 some of the phlogistic particles. Next, let it be dissolved, 

 filtered, and set to crystallise again ; then let it be treated 

 with nitrous acid. The vinegar may perhaps, by such a 

 combination, acquire more fixity ; so that the nitrous acid 

 shall be able to produce a greater change. Should it pass 

 over again in the form of vinegar, let it be combined once 

 more with calcareous earth, and let the foregoing experiment 

 be repeated, in order to try whether some sensible change 

 will not ensue. Should this method fail, let the opposite 

 be tried ; endeavour to add more gross phlogistic matter to 

 the vinegar ; try to combine strong vinegar, and that of 

 Westendorf, with unctuous oils (see Macquer's Diet., Th. ii. S. 

 126, G. T.), as for instance with oil from tartar, by means 

 of digestion or distillation ; and afterwards it may be joined 

 with calcareous earth. Thus we might attempt to bring it 

 nearer to tartar, and again, by means of nitrous acid, to 

 convert it into acid of sugar. 



EXTRACT OF A LETTER FROM DR. CRELL TO MR. 

 D'ARCET. 1 



The chemists have always been much occupied in the 

 investigation of the nature of the vegetable acids ; and the 

 discovery of their constituent parts would certainly be an 

 1 Journal de Physique, October, 1785, p. 297. 



