£60 On Gum Arabic and Gum Adraganth. 



vcrc coiDposed of the same principles as those of the red 

 gum. Further, in washing; there was extracted a small 

 quanlitv of alk:'.li, viz. potasli. 



3. Ten grains of gum arabic, burnt like the others, left 

 tlnce decitirammes of ashes, which were composed of the 

 same elements with the preceding; with this ditlerenee, 

 however, that thev gave no symptoms of the presence of 

 an alkali, nor of sulphur, as the others. 



1 had fornicrlv suspected that the opacity of gum adra- 

 ganth, and the ditliculty which it has to dissolve in water, 

 were owing to the existence of a very great quantity of 

 earthy matter ; but after these expcrijiients it appeared they 

 were owing to another cause. 



To a cenaintv the lime is not found in the stale of a car- 

 bonate, and still less in the stale of cjuicklime ; for the so- 

 lutions of gum are not alkaline, they are, on the contrary, 

 sliirhtly acid. At least, if one rub on a morsel of gum a 

 piece of test paper well moistened, it is sensibly reddened. 

 It is certain, also, that oxalate of ammonia and carbonate 

 of potash occasion precipitations in the solution of gum 

 arabic, and that the acetate of lead is not there formed at 

 all. It follows from thence that there is lime in the gums, 

 combined with an acid : — But what is this acid ? 



Here, for want of facts, I shall be obliged to give way 

 to conjecture ; but conjecture very probable, which every 

 thing seems to support, and nothing to contradict. It is not 

 doubtful, at least, that it is a vegerable acid ; for, on being 

 decomposed, they leave their bases combined with carbonic 

 acid. 



Supposing this, let us see among the great number of 

 acids that which could best satisfy all those conditions. 

 It is neither the oxalic, nor the tartareous acid, nor the 

 citric, because their combinations with lime are insoluble 

 in water, and likewise because they exist in only a small 

 number of vegetables. Still less can it be the benzoic, the 

 irallic, the vuisoxaiic or the honistic acid ; which, as we 

 know, are very rare in nature, and of which the three first 

 form also salts which are very little soluble. 



It remains, therefore, only to choose between the acetous 

 and the malic acid. The first forms, as we know, soluble 

 combinations w iih all known substances with which it is 

 capable of uniting; some of them are feven deliquescent. 

 It is, besides, a result most frequent in the operations of 

 nature in the vegetable and animal system ; since it forms 

 itself by vegetation, fermentation, the action of powerful 

 acids, and the influence of heat. 



The 



