251 
of a nezvly discovered vegetable acid. 
on this account, be a period when the latter will disguise the 
former, and yet the lead will be still present. I would there- 
fore suggest the substitution of sulphuretted hydrogen in 
place of sulphuric acid. 
If it were required to obtain malic acid exceedingly pure, 
and still more divested of vegetable matter, the following 
process may be adopted. 
The juice of Sempervivum Tectorum is to be evaporated to 
two-thirds, and, after standing some hours, it is to be filtered, 
and mixed with an equal quantity of alcohol. The coagulum 
is to be separated by the filter, edulcorated with fresh por- 
tions of alcohol, and dried in the air, lest any adhering alcohol 
should impede its subsequent solution. The mass is then to 
be dissolved in water, mixed with solution of acetate of lead, 
and the precipitate collected on a filter. After being well 
edulcorated from any superfluous acetate of lead, the preci- 
pitate is to be boiled for 15 minutes with a little less of dilute 
sulphuric acid than is sufficient to saturate the oxide of lead : 
and for this part of the process, the criterion of sweetness 
will very well answer the purpose. The whole is to be set 
aside for some days, and, during this period, a small quantity 
of sulphate of lead which the malic acid held dissolved, will 
be deposited. The liquor is now to be filtered, and in 
order to separate the last portions of lead, a stream of sul- 
phuretted hydrogen is to be transmitted through it: the 
black precipitate is to be filtered off’, and the liquor should be 
boiled in a vessel freely exposed, until paper moistened with 
acetate of lead is no longer blackened by the discharged va- 
pour. This acid is the purest that can be obtained ; it retains 
K k 2 
