ON THE ACID OF LEMONS 261 



tion of the whole, I then poured it out upon a filter, and 

 evaporated the acid liquor which passed through; but it 

 could not be made to shoot by these means. 



I therefore concluded the great quantity of saponaceous 

 matter which the spirit holds in solution is the impediment 

 to crystallisation. In order to separate it, I employed the 

 same method that is followed when the essential acid of 

 tartar is to be obtained from cream of tartar. I saturated 

 the lemon juice, as it was boiling in the cucurbit, with 

 pulverised chalk, the weight of which was observed ; the 

 compound fell immediately to the bottom in the form of a 

 middle salt, nearly resembling tartarised lime. The water, 

 at the bottom of which the precipitate lies, contains the 

 saponaceous and mucilaginous matter, and the pure acid 

 remains in combination with the calcareous earth. The 

 precipitate is to be edulcorated with lukewarm water, till it 

 appears colourless on being poured off. The compound 

 agrees with gypsum, in being very sparingly soluble in water. 

 There is next to be added to it a quantity of English oil of 

 vitriol, diluted with ten times its bulk of water, equal in 

 weight to the chalk used for saturating the juice. This 

 mixture is to be boiled in the cucurbit for a few minutes. 

 When the whole has grown cold, the acid is to be separated 

 from the gypsum by means of the filter, and to be treated 

 in the same way as the acid of tartar. It is, however, 

 necessary to try, by evaporating the acid to the consistence 

 of a thin syrup, whether it still contains any calcareous 

 earth. This appears upon mixing a small quantity with 

 oil of vitriol, as in that case there will be a precipitation 

 of gypsum; and it will be necessary to add more oil of 

 vitriol to the whole quantity of acid, as the presence of a 

 small quantity of lime in solution totally prevents the 

 crystallisation. The crystals will shoot just as well in a 



