176 
MISCELLANY. 
quum subsederit Bitartras Potassas cola. Colato adde aquae quantum 
sufficiat ut sint totius liquoris drachmEe quinquaginta, ^h.—'^y'i. ^ij. 
Acidum hoc Hydriodicum liquidura, habet lodinii, gr. v. , in singulis 
drachmis. 
It is a fact well known to physiologists, says Dr. B., that when 
free iodine is introduced into the stomach, it is speedily converted 
into hydriodic acid. This conversion is probably effected differently in 
different cases. If a large quantity of uncombined iodine be swallowed 
when the stomach is empty, the hydrogen with which it combines may 
be furnished in part by the gastric juices, but it can scarcely be doubted 
that it is chiefly supplied from the tissues of the stomach itself, which 
undergo corrosion. When, however, the iodine is given in combination 
with starch, it is probable that the starch, M'hile under digestion, furnishes 
the hydrogen which goes to form the hydriodic acid, and in this way the 
starch defends the tissues of the stomach from the corrosive action which 
they would otherwise undergo. It appeared to me, however, that it would 
be well to save the stomach the labour of preparing the hydriodic acid, 
by giving, for the purposes of medicine, not free iodine, but the hydriodic 
acid itself. 
I was the more inclined to make this experiment, as it would enable 
us to determine, from direct evidence, whether the opinion, rendered so 
probable by general reasoning, be also borne out by experience, that hy- 
driodic acid closely resembles iodine in its effects upon the body, and is 
in reality the active principle to which the ordinary preparations of iodine 
owe their medicinal efhcacy. The trials made of the hydriodic acid as a 
medicine fully realized the expectations entertained of it. 
The processes recommended in works upon chemistry for forming hy- 
driodic acid are not well adapted for the purposes of medicine, both on 
account of their complexity, and because they do not yield an acid of 
which the strength is uniform and easily estimated. The strong mineral 
acids cannot be employed in decomposing the iodides to form hydriodic 
acid, as is done in forming muriatic acid from common salt, because those 
acids react on the hydriodic acid as it is generated. The tartaric acid, 
however, is not liable to the same objection ; and I found on trying the 
experiment of treating iodide of potassium with tartaric acid, in the pro- 
portions necessary to form cream of tartar, that hydriodic acid was readily 
obtained in a state of sufficient purity for the purposes of medicine, 
although holding some cream of tartar in solution. To diminish as much 
as possible the quantity of cream of tartar dissolved, the acids and salts 
are each dissolved in a very small quantity of water, the rest of the water 
not being added till the precipitated cream of tartar has been removed by 
filtering. The liquid acid thus obtained has an agreeable sourness. It 
is at first limpid, or with only a slight yellow tinge, but as happens to 
this acid, in whatever way prepared, on being kept it soon assumes first 
