508 



are the same, or that apples contain no other acid. Vauque- 

 lin, it is true, inefFectually sought Scheele's acid in sorbus 

 berries ; but neither he nor Braconnot made trial of apples. 

 The question of identity was therefore left undecided : it was 

 still possible that malic acid, such as Scheele described, might 

 exist in apples, along with sorbic, inasmuch as no experiments 

 have hitherto been published which directly disprove his state- 

 ments. Under these circumstances of doubt, 1 thought it 

 right to undertake the inquiry ; and I now purpose to adduce 

 facts which will supply what was deficient in our means of de- 

 termining the question. 



*' When the juice of unripe apples is mixed with solution 

 of acetate of lead, a curdy precipitate separates abundantly. 

 If this be filtered ofi^, and boiling water be allowed to run 

 through it, the water as it passes being received in a number 

 of vessels, it will be found that crystals will sooner or later 

 form in several of the first vessels, and none in the last : nor 

 will any further aff"usions of boiling water on the pasty mass 

 remaining on the filter furnish a single crystal. In order to 

 obtain a further product of crystals, the pasty mass must be 

 decomposed by dilute sulphuric acid ; the sulphate of lead is 

 to be washed with much water, the whole to be filtered, and 

 the clear liquor again mixed with solution of acetate of lead, 

 which will cause a new precipitation. The precipitate, filtered 

 ofi", is to be treated as before with boiling water, and the liquor 

 received in difi^erent vessels. Crystals will form in the first 

 vessels, and none in the last. The pasty mass is still capable 

 of furnishing crystals by a repetition of these processes. No 

 one before me had ever procured these crystals from apple- 

 juice ; their properties had never been investigated ; the extent 

 to which, by repetition of the foregoing processes, crystals 

 could be produced, had never been ascertained ; and, conse- 

 quently, it was not known whether the whole mass is convert- 

 able into crystals, or whether a portion of it would remain 

 uncrystallizable, which might contain an acid corresponding 



