564 
LECTURES ON THE BRITISH PHARMACOPOEIA. 
poeia operations with sulphuric acid, lead is got rid of by mere dilution. The 
operation, however, it must be admitted, has this advantage, that arsenic, the 
third chief impurity in commercial sulphuric acid, may also be thereby removed. 
Since the Pharmacopoeia was printed, some researches by Bussy and Buignet 
(Journ. de Pharm. et de Chim. vol. xliv. p. 177, and Chem. News, vol. ix. p. 73) 
on the purification of arseniferous sulphuric acid have been published, from 
which it appears that,—first, when arsenic is present as arse life acid (As 0 5 ), 
it invariably remains behind in the retort when the sulphuric acid is distilled ; 
second, that when present as arsemews acid (As 0 3 ), it invariably accompa¬ 
nies the rectified sulphuric acid; and third, that the addition of a little nitric 
acid to, or its presence'in, sulphuric acid ensures the oxidation of arsenious and 
arsenic acid. So, then, in the examination of sulphuric acid with a view to 
purification, the course to be adopted seems to be as follows :—Test for arsenic 
by the hydrogen test, and for nitrous compounds by adding a small quantity of 
powdered sulphate of iron, which acquires a violet tint if they are present. If 
both or only nitrous compounds are found, then add sulphate of ammonia, and 
distil. If nitrous compounds are absent and arsenic is present, first heat with 
a little nitric acid, and then add sulphate of ammonia, and distil. If both are 
absent, distillation is scarcely necessary. As the process stands at present, lead 
will be eliminated, nitrous compounds will be got rid of, if present, and arsenic 
may or may not be removed from the acid. 
Acidum Sulfiiuricum Dilutum.— Is slightly stronger than the Dublin ; 
slighter, weaker than the Edinburgh; and about one and a half per cent, weaker 
than the old London acid. 
Acidum Sulpiiurosum. —In directing “ sulphuric acid ” to be used in the 
preparation of sulphurous acid, the words u of commerce ” have obviously been 
omitted, the use of the distilled acid being even less necessary here than in the 
preparation of Sodce Phosphas , where “ Sulphuric Acid of commerce” is ordered 
to be employed. [The words are also omitted from the smaller edition of the 
Pharmacopoeia.] 
Acidum Tannicum.— Neither the London nor Edinburgh Pharmacopoeias 
gave a process for obtaining tannic acid ; that now given is from the Dublin 
work, and is, in fact, Pelouze’s process of percolating galls with ether. It is 
important that the officinal ether, that containing eight per cent, by volume of 
alcohol, be used ; for Sandrock has shown (Pharm. Journ. vol. xii. p. 597) that 
neither pure ether nor pure washed ether gives satisfactory results, but the pro¬ 
cess is rapid and successful if the ether contains one part of alcohol to every six¬ 
teen of ether. It may be interesting to state here, that with regard to the lower 
of the two layers of liquid obtained in the receiver of the percolator in the pro¬ 
cess, Bolley has shown (Chem. News, vol. ii. p. 270) that it is not, as Pelouze had 
said, a concentrated aqueous solution of tannic acid, nor, as Mohr had said, a 
concentrated solution of tannic acid in ether, but a solution in equal volumes of 
ether and water. This quite accords with the previous observation of Luboldt 
(Journ. fur Prak. Chem. vol. lxvii. p. 357), that the lowest of the three layers 
of liquid obtained on treating tannin with ether and water is a hydrate of tannic 
acid dissolved in etherated water. 
Aconitia.' —A process somewhat similar to the new one given for the prepara¬ 
tion of aconitia in the Pharmacopoeia is described by Liegeois and Ilottot (Journ. 
de Pharm., Aug. 1863). This French process was afterwards, however, stated 
to be of English origin (Chem. News, vol. viii. p. 200),—a statement that quite 
accords with that of Garrod, from which (Med. Times and Gaz. 1864, vol. i. 
p. 359) it may be inferred that the Pharmacopoeia process was supplied by some 
English Pharmaceutists who make aconitia largely. The process seems to be 
excellent, for one-thirtieth of a grain of the alkaloid prepared by Liegeois and 
Ilottot killed a frog in four minutes, while a grain and a half of the most active 
