260 ESSAY XXIV. 



respect to every other method for the purification of the 

 lixivium (those of Scopoli and Westrumb l not excepted), I 

 am convinced that they are imperfect ; for it is only necessary 

 to boil a sufficient length of time their yellow solution with 

 vitriolic or muriatic acid, and Prussian blue will be separated. 

 My salt continues unaltered, even when exposed to the open 

 air ; for the iron strengthens the connection between the 

 colouring acid and the alkali, and fixes it so that the aerial 

 acid cannot expel it ; which otherwise will happen in a few 

 days, provided it be not combined with iron or some other 

 metal in the colouring ley. I have not yet observed whether 

 the tinging acid, for such is the name which Professor 

 Bergmann has bestowed upon it, saturated with alkali or lime, 

 will yield crystals ? If you desire to know this, the 

 combinations and evaporations must be performed in close 

 vessels. 



ON THE CRYSTALLISATION OF THE ACID OF LEMONS. 2 



It has hitherto been a matter of doubt whether the 

 juice of lemons could be reduced to the form of crystals ; 

 for it appeared, from a great variety of experiments, that 

 this juice, though evaporated to the consistence of a syrup, 

 would not shoot into crystals. I was led to make some 

 trials upon this subject, which I have communicated to our 

 Academy of Sciences, and which point out the method by 

 which I at length accomplished my purpose. I conjectured 

 at first that the mucilaginous matter in the juice prevented 

 its crystallisation ; on which account I mixed the inspissated 

 juice with strong spirit of wine, and thus produced a coagula- 



1 Mr. Scheele means here the method proposed by Mr. Westruml) in his 

 " Essay on the Constituent Parts of the Blood and the Lixivium Sanguinis " 

 (Crell's Neueste Entdeck), and not that alluded to in the last note. T. 



2 Crell's Chemische Annalen, Th. vii. S. 3. 



