44 Purificaikn of tht Acid ef Lemons. 



the evaporation. The mafs of cryftals which was taken out, after cooling and three days 

 Tcpofe, was confiderable and black. 



I fufFered this faline mafs to drain in oCer balkets, while the evaporation and cryftalliza- 

 tion of the remaining fluid were performed. When this firft operation was ended, the whole 

 of the faline mafs was re-diflblved in a fufficient quantity of cold water, and filtered through 

 ftrainers of linen, covered with filtering paper. 



The folution which paflTed the filter was clear, but of a dirty brown, and the greateft 

 quantity of the matter which had blackened the cryftals remained behind. This was again 

 evaporated, left to cryftallize, and in this manner exhaufted of the citric acid. The 

 cryftals were now' yellow, and more regularly figured. By a third folution, filtration, 

 and evaporation, the cryftals were again obtained white, regular, and of the greatefl 

 purity. The black matter depofited on the filter was fo trifling that it formed a very 

 flight covering. 



Scheele, who was content with having proved the poffibility of obtaining this vegetable 

 acid io a concrete ftate, could not determine its natural form, becaufe he operated on fuch 

 fmall quantities. 



My refults afforded cryftals as large as are ufually obtained from the ordinary procefles 

 of faline folution, and as %afily to be defcribed. They prefent, on fimple infpeftion, 

 rhomboidal prifms, the fides of which are inclined to each other in angles of about 120 

 and 60 degrees, terminated at each end by four trapezoidal faces which include the folid 

 angles. 



I have before remarked, that Scheele had obferved, as one of the conditions eflentlal to 

 the ready cryftallization of the citric acid, to add a fmall quantity of fulphuric acid in ex- 

 cefs beyond the exa£l quantity neceflary to decompofe the calcareous citrate. The remark 

 of this chemift not being followed by any explanation, my trials in the large way have 

 proved the great difcernmenc of the chemift of Gottingen ; and that, if he had operated 

 on a quantity of lemon juice equal to that which I purified, he would have afcertained 

 the reafons why this excefa of acid was found to be necelTary in his more confined expe- 

 riments. 



Having afcertained that the black matter remaining on the filters in this procefs is char- 

 coal, it follows that it could not have been afibrded but at the expence of a confiderable 

 portion of the mucilaginous matter of the lemon juice, which the citric acid had carried 

 with it in its combination with the bafe of the calcareous carbonate ; and that afterwards 

 when the citrate is decompofed, the excefs of fulphuric acid is required to decompofe this 

 mucilage, and precipitate the carbone, as foon as the fluid begins to be condenfed by eva- 

 poration. The ingenious experiments of Fourcroy and Vauquelin prove the nature of the 

 aition of fulphuric acid on vegetable matter, and ftrongly confirm my inductions *. 



Lemon 



* Forthcfe important txperiments fee Philof. Journal I. 3S5.— In order to (hew that mucilage enters into the 

 citrate of lime, and that it is docompofed by fulphuric acid, itfeems neceflary to make the experiment with only 

 a very tninure excefs of the latter. Scheele thought the acid (Eflfays, p. 361.) in the citrate to be pure, aud 

 he required an excefs of fulphuric acid to be added to infure the faturation of the whole of the lime. I would 

 propofe to the confideration of the Jeamed author of thii paper, to afcertain whether it be not a ponion of the 

 acid itfelf wliich is altered and made to dcpofit carbone. If fo, the lefs the furplus of fulphuric acid the better : 



4 b»t. 



