REMARKS ON THE ACIDS OF THE BRITISH PH ARM ACOPCEIA. 
65 
2 H 2 S 0 4 + C = 2 H 2 O + C 0 2 + 2 S O a . 
Carbonic and sulphurous anhydride are therefore produced; the latter is 
absorbed by the water, and combines with it to form sulphurous acid, H 2 SQ 3 . 
By freezing the solution, crystals of this acid can be obtained. 
Sulphurous acid of the Pharmacopoeia contains ITS per cent, of H 2 SG 3 , 
corresponding to 9'2 per cent, of S O s . 34‘7 grains of it discharge the colour 
of 1000 grain-measures of the volumetric solution of iodine. Sulphurous 
acid is converted by iodine, in the presence of water, into sulphuric acid, hy- 
driodic acid being simultaneously formed. 
H 2 S0 3 + Ho0 + Io=H 2 S0 4 + 2H I. 
One molecule of sulphurous acid requires two atoms of iodine, conse¬ 
quently, as 100() grain-measures of the volumetric solution contain T Vth of 
an atom in grains of I, 34‘7 grains of the acid must contain half a molecule 
in grains of H 3 S O s , corresponding to half a molecule of S 0 2 . 
Acidum Tannicum. —The process now given for this acid is the one gene¬ 
rally adopted by the manufacturer. . Instead of percolation with ether, the 
galls are allowed to become damp, then .made into a paste with ether, and 
submitted to expression. A strong aqueous solution of tannin is obtained, 
which is evaporated to the consistence of a soft extract, and dried in an oven. 
It vesiculates and swells out into a mass of thin scales. 
Acidum Tartaricum.—No change has been made in the process for pre¬ 
paring this acid. Acid tartrate of potash is boiled with water, and chalk 
added:— 
2 HKC 4 H 4 0 6 + CaC0 3 ==K 2 C 4 H 4 O fi + Ca" C 4 H 4 O e + H 2 O + C0 2 . 
Then chloride of calcium is added, to decompose the neutral tartrate ot potash. 
Ko C 4 H 4 O e + Ca Cl 2 = Ca" C 4 H 4 O g + 2K Cl. 
The tartrate of lime, formed by these two reactions, is washed and decom¬ 
posed by sulphuric acid. 
Ca C 4 H 4 O g + H 2 S 0 4 = Ho C 4 H 4 O e + C a S 0 4 . 
The solution is evaporated and crystallized. Half a molecule, or 75 grains 
of the acid, require 1000 grain-measures of the volumetric solution of soda 
for neutralization. 
Diluted Hydrochloric, Nitric, and Sulphuric Acids. —These acids 
are of the same strength as before, being so arranged that six fluid drachms 
of each shall exactly suffice to saturate' one‘molecule in grains of an alkali 
or alkaline bicarbonate. * * ‘ 
Two methods of preparation are given, one of which is somewhat novel. 
The strong acid is weighed in a glass flask, which is then tilled up with 
water to a mark on the neck. This plan of operating admits of the utmost 
accuracy, while it is as easy of execution as the ordinary method. Common 
measure glasses are, as a rule, very roughly adjusted, and quite inadequate 
where anything like precision is required. The measuring flask now intro¬ 
duced is such as is usually employed in volumetric processes ; it may be 
purchased for a very small sum, or the operator may graduate one for him¬ 
self in less than ten minutes. It is only necessary to select a common flask 
which, when containing a pint of w 7 ater, is filled to about the middle of the 
neck. The flask is dried, balanced in a good pair of scales, and 7000 grains 
(]. lb. 4 oz.) of water at 60° carefully weighed in. A mark is then made on 
the neck with a file at the level of the liquid. As the water forms a meni¬ 
scus in the neck, it is better to take the bottom of the curve as the point 
to mark. It is much easier in all volumetric instruments to read from the 
bottom than the top of the curve. 
{To be continued.) 
VOL. IX. 
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