PYROLIGNEOUS ACID FOR PHARMACEUTICAL PURPOSES. 
53 
Tiie cover shonld be made of pore tin, and 
united with a refiigatory, whose tube is also 
formed of the same metal- Priickner considers 
norcelain preferable to tin for the composition 
of the cover, or rough burned c]ay (nicht durch- 
switzender), the latter of which he himself 
employs. 
'I'o prevent the melting of the tin, when that 
metalis employed, it is necessary to separate it 
from the iron of the retort by means of a stripe 
oflinen;a Intins of lime and fine sand then 
serves to unite the cover and belly of the retort. 
Larger retorts are not desirable, because, to- 
wards the end of the distillation, decomposition 
of the acetic acid is readily produced, in con- 
sequence of the destruction which a portion of 
the mass in contact with the bottom undergoes, 
while all the acid contained in it is driven off. 
The distillation begins with a gentle fire, and 
should be carried on without increasing the 
heat, until the liquid passing over begins to 
produce a yellowish colour in the distilled li- 
quid. It is not worth while to obtain the last 
portions of the acid, because the educt is im- 
purp,and sulphnrbegins soon to sublime. 
From the 251bs. of acetate of lime are ob- 
tained 25 to 27 parts of acid. 3’he gypsum 
remaining in the retort can be easily removed. 
It contains some free acid, which may be 
washed out and preserved for further use. By 
the action of the sulphuric acid upon the acetate 
of lime, a sulphurous smell will be perceived, 
wbicli also exists in the weak acid which pass- 
e.s over hrst. This arises from a partial de- 
composition of the snlphuiic acid, in conse- 
quence of which sulphurous acid is disengaged. 
To diminish, as much as possible, the quan- 
tity of this in the whole distilled liquid, the first 
tenth is removed. The subsequent distillation 
is continued until the liquor passing over be- 
gins to lose its pure water colour. The last 
portions will, therefore, be separated and mixed 
with (he acid which passed over first, for the 
purpose of being further purified. 
The acid obtained in the manner described, 
possesses generally the specific gravity of 
l•045 — 1'050, is colourless, like water, arid re- 
tains still a trace of the oiiginal einpyi>umatic 
odour. 
It contains also some sulphurous acid, and 
possesses corresponding cliaracters, but loses 
it after being exposed for some time to the air, 
in open vessels, the acid being converted into 
snlpliuric acid. 
U is obvious, from the quantity of acid re- 
commended, that, for the decomposition of the 
acetate of lime, an excess ofsulphuiic acid i.s 
necessary ; since, for 100 parts of dry salts, 62 
parts of acid, excluding stechiornelrical quan- 
tities, would be sufficient. The peculiarity of 
Priirkner's process, he considers to consist in 
lliese pioportions ; and he has found tiiat the 
addition of the excess of sulpluiric acid is the 
most powerful method ofdestioying or decom- 
posing the empyreumatic matter existing in 
the pyroligneous acid. In consequence of inat- 
tention to this circumstance, the methods of 
purification pointed out by several chemists, 
especiallv tiiat of B. Stolze, in his woik, 
" Giiindliche r.nleitung die rolie Holzanre zu 
reinigen,’ &c,, must be. either useless or very 
inefficient. The method of previously heating 
tlie acetate of lime, and of abolishing the dry- 
ing in an open vessel, over a free fire, is a 
decided improvement. For thii.s, there is an 
inconsiderable, or no loss by the flerom[) 08 it!on 
of the acetate of lime, with the least possible 
waste of time and fuel. For manufacturing 
purposes, as for making acetate of lead, and 
acetate of copper, there is no need of repeated 
distillation, because the sulphurous and sul- 
phuric acid can readily be separated in the 
following manner : A quantity of liquid di.s- 
acetate of lead is to be prepared, to about a 
pound of w’iiich the distilled arid is to be add- 
ed, until no more preci[)itate of sulphate of 
lead falls. The latter should be collec ted and 
weighed. 'I’he quantity of sul[ihuric acid in 
a given quantity of the acid, being thus know’n, 
it is easy to calculate how much of the acetate 
of lead solution w ill be required to throw down 
the whole acid in the acetic acid. Some sul- 
phate of lead is held in solution, w hich is of 
little consequence in the manufacture of sugar 
oflead. 
FUB.THER PURIFICATION OF THE 
PYROLIGNEOUS ACID.— For chemical 
and pharmaceutical puiqmses, it is necessary 
to have pure concentrated acetic acid. To 
accomplish this the snlplinrous acid in the 
distilled acetic acid should be digested for a 
short time wdth finely pulverized brown-stone, 
and a little wood or animal charcoal. One 
pound of brownsfone and ^ pound of animal 
charcoal are sufficient for from 25 to SGlbs. of 
acid. 
The supernatant liquid after the precipitate 
has been allowed to subside during 12 hours 
should be decanted off, transferred into a retort 
and rectified by a second distillation to dry- 
ness. The acid pa.sses over pure and coloni les.s, 
and destitute of any .smell, save of acetic acid, 
having a specific gravity of from T042toT049, 
or 7® or 8® by Beck’s areometer, and may be 
used for all chemical purposes. According to 
the custom of the trade, and of the French 
manufacturers, a portion of acetic ether may 
be added to the acid, by which mixture the 
smell becomes more pleasant. 
Supilement.— Accovdintx to A. Richter, 
chemical manufacturer at Konigs.saal, in Bo- 
hemia, with whom Pi iickner corresfionded on 
this subject, it appears, that when the pure 
acid, obtained by tlie process described, i.s 
neutralized by cai bonate of potash, and then 
some strong potash lye is added, it still retains 
a yellow colour, from the presence of an oxy- 
dizable body, of which it i.s difficult to free 
the acid, Priickner, during the course of last 
summer, in his researclie.s, fell upon a method 
of affecting the sepaiation of this substance. 
Pyroligneous acid is not precipitated by in- 
fusion of gails, and even after some time no- 
thing falls. If however tincture or infusion of 
galls be poured into a solution of pyroligneous 
acid salt, as of raw acetate of lime (or acetate 
ot potash) a daik reddish purple precipitate 
subsides, which contains a salt of tannic acid. 
The previously blackish brown liquid becomes, 
clearer and transparent like Rhenish wine, 
and leaves after filtration and evaporation to 
dryness, by being placed for several days in 
a temperature of 70^ or 80’^ B . 189® or 212'^ F.) 
