1 16 Refe arches ref peeling the 



but weak, makes its appearance, which (hows that the aftrin«< 

 gent principle is only in fmall quantity. 



The citrate of lime kept under water, expofed to the furl 

 during the heat of fumnier, becomes putrid, and the water 

 is covered with a (tony cruft, which is carbonate of lime. 

 The citric acid, like the other vegetable acids, is deftroyed 

 by putrefaction. Its carbonaceous part united to the oxygen 

 of the water, which is decompofed, and thus transformed 

 into acid, reproduces chalk: this putrefaction is always ac- 

 companied with an efcape of bubbles, which are only car- 

 bonaceous hydrogen, 



VII. Decompojition of the Citrate of Lime hy Sulphuric Acid. 



To expel the carbonic acid completely from 4 ounces of 

 chalk, it was neceffary to employ 20 ounces of diluted ful- 

 phuric acid (of 19 degrees of Baume's areometer). This 

 acid is made by mixing three parts of water with one of com- 

 mon oil of vitriol : if the latter is not well concentrated, the 

 water muft be diminifhed, and, by fome trials, the diluted 

 acid may be brought to the required point. 



To feparate the citric acid united to a bafe of four ounces 

 of chalk, it is evident that the above quantity of fulphuric 

 acid muft be fufficient. This quantity, therefore, amounts 

 to five times the weight of the citrate, or 500 per cent, of 

 this earthy fait. 



I heated to ebullition fix ounces of citrate with two pounds 

 of water, and added 30 ounces of my fulphuric acid of 19 : 

 after being expofed to ebullition about feven minutes, taking 

 care to ftir the mixture with a fpatula, the whole citrate was 

 found changed into a calcareous fulphate. The mixture 

 being then ftrained through filtering paper, and left to evapo- 

 rate, depofited fulphate ; and four fucceffive evaporations and 

 filtrations were neceflary to free it entirely from its earthy 

 depofits. 



The feparation of this fulphate may be abridged by mixing 

 the liquor, evaporated to the confidence of bright fyrup, with 

 a certain quantity of fpirit of wine ; and this is even the pro- 

 cefs which ought to be followed on all occafions when it is 

 required, without having a very large quantity of citric acid, 

 to obtain it as pure as poffible. 



The confidence of bright fyrup is not, however, the point 

 at which the citric acid can cryftallize, it muft be carried to 

 that of baked fyrup, becaufe this acid takes up very little 

 water in its cryftals. By two cryftallizations I obtained 3^. 

 ounces, or 28 drams, of pretty large cryftals* The two drama 



wanting 



9 



