250 Mr. Donovan on the nature and combinations 
The solution is to be filtered, the filtered liquor to be mixed 
with alcohol, and the coagulum thus obtained, is to be edul- 
corated with new portions of alcohol. The coagulum is then 
to be dissolved in water, and mixed with a solution of acetate 
of lead : a precipitate falls, which is to be treated with sul- 
phuric acid, in the manner already directed. 
No one who has not gone through this process, can fully 
conceive the difficulty and expense of it : and I have found that 
the acid obtained is variable in its nature. In one case I obtained 
an acid, which, when mixed with solution of acetate of lead, 
did not at first produce any effect, but at length slowly depo- 
sited a precipitate. The heating of another portion of the 
acid with carbonate of lime, produced a separation of a black 
powder, which possessed the properties of charcoal. There 
were also many other peculiarities ; and the combined effect 
of all was to convince me, that great differences exist between 
the acid obtained in this manner, and that obtained by other 
processes. 
The experiments of Vauquelin satisfied him that the acid 
which is combined with lime in the Sempervivum Tectorum, is 
the true malic : and all my trials convince me, that it does 
not contain even the least quantity of the sorbic. Since then, 
by the means generally employed, we do not obtain malic 
acid, the only alternative is to adopt the hitherto neglected 
process of Vauquelin ; and it will be found that his process 
affords the acid with greater ease, and in much greater purity, 
than any other. The method of detaching the acid from the 
malate of lead by sulphuric acid is, as we have seen, difficult; 
and the criterion of the taste is liable to this fallacy, that as 
the sourness increases, the sweetness decreases. There will 
