August 3, 1872.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
81 
EXPERIMENTS ON COMMERCIAL IODIDE 
OF POTASSIUM. 
BY W. B. BISHOP, 
Student in the Laboratory of the Pharmaceutical 
Society . 
Some time ago, M. Lepage published in the ‘ Jour-1 
nal de Pliarmacie,’ a process for estimating volu- 
metrically, iodide in the presence of bromide of pot¬ 
assium. The method he adopts is based upon the 
property possessed by perchloride of mercury of 
precipitating the iodide to the exclusion of the 
bromide, the bromide of mercury being soluble in 
water. After having ascertained by previous tests 
that the iodide under examination is free from chlo¬ 
ride, carbonate and iodate, 1 gram of the iodide is 
dissolved in 80 c. c. of distilled water. A solution of 
1 gram of perchloride of mercury in 20 c. c. is also 
prepared, and the latter dropped from a burette into 
the solution of the sample to be tested until it ceases 
to form a precipitate. If the iodide be pure, 16 c. c. 
of the solution are sufficient for this purpose. Frem 
the above data may be calculated the real amount 
of iodide in the solution. To detect the bromide in 
the supernatant liquid, it is left some time at rest, 
then decanted on to a filter so as to obtain it per¬ 
fectly clear. This is then evaporated in a capsule 
till its volume is reduced to about 20 c. c.; after 
cooling, it is poured into a tube and mixed with a 
few drops of a solution of perchloride of iron. On 
boiling, the vapour of iodine is given off, and may 
be easily recognized by placing at the mouth of the 
tube a piece of starch paper. When the last traced 
of iodine have been expelled, the solution is filtered, 
and the clear liquid mixed with a little chlorine 
water, which sets the bromine at liberty and colours 
the solution strongly yellow. On agitation with a ; 
few grams of sulphide of carbon, the bromine is 
removed and furnishes a yellow solution in which it 
can be recognized by the usual tests. This process 
will answer under careful manipulation and is at first 
sight a promising one, but it has some defects which 
interfere with the accuracy of the results obtained 
by it. In the first place the iodide of mercury does 
not settle very readily, and even by filtration it is 
very difficult to remove the suspended red particles. 
It is, moreover, rather troublesome to have to filter 
a liquid two or three times on the addition of each 
drop of the test, and certainly leads to loss. There 
can also be little doubt that the mercuric iodide is 
not by any means insoluble in the alkaline chloride 
and bromide retained in the mother liquor, and thus 
another source of error is introduced. A more con¬ 
venient method consists in the employment of a 
standard nitrate of silver solution in the place of 
perchloride of mercury. A weighed quantity of the 
iodide of potassium is dissolved in a little water, and 
I find a stoppered bottle the most appropriate vessel 
in which to perform the experiment, as the liquid 
may be more conveniently shaken in it. The 
standard solution of nitrate of silver is then run in 
from a burette, taking care to shake well after each 
addition. When nearly enough has been added, the 
precipitate will be seen to coagulate and fall to the 
bottom. Enough nitrate of silver solution is added 
to make the supernatant liquid perfectly clear. 
The following 10 specimens have been examined 
by the foregoing process:— 
Third Series, No. 110. 
Percentage of 
iodide of potassm. 
in the dry salt as 
Water. 
Chloride. 
Carbonate. 
Iodate. 
indicated by 
the AgNO s . 
99-2 
•47 
none. 
very faintly 
alk. 
none. 
93 6 
•59 
none. 
alkaline. 
large 
quantity. 
102-8 
*45 
large 
quantity. 
faintly alk. 
none. 
100.8 
•36 
trace. 
neutral. 
none. 
100-0 
•58 
none. 
neutral. 
none. 
98 8 
1-58 
faint trace. 
very alk. 
trace. 
99 7 
•33 
trace. 
alkaline. 
trace. 
991 
7 
none. 
alkaline. 
none. 
100-8 
2-1 
trace. 
neutral. 
none. 
100-3 
1-5 
trace. 
very faintly 
alk. 
none. 
It will be seen that in some cases the percentage- 
of iodide indicated in the table is greater than lOO. 
This arises from the presence of chloride of potas¬ 
sium, for in no case was any appreciable quantity 
of bromide detected. The equivalent of chloride 
and bromide of potassium being less than that of the 
iodide, it follows that these salts will consume 
more of the solution of nitrate of silver than an 
equal amount of iodide. Advantage has been taken 
of this circumstance in calculating the percentage 
of chloride in bromide of potassium by E. Baudri- 
mont* and Falieresf in a recent number of the 
‘ Journal de Pliarmacie.’ 
It will be seen by reference to the tabulated state¬ 
ment of the results obtained by myself that the 
iodide of potassium of commerce may be considered 
to be remarkably pure, considering its present high 
price. It certainly appears to be free from adulte¬ 
ration. 
THE MICROSCOPE IN PHARMACY. 
BY HENRY POCKLINGTON. 
('Continued from page 63.) 
Scammonlze Radix.— With the superficial appear¬ 
ance of this root every pharmacist is familiar. Its 
microscopic characters are more difficult to become 
familiar with, and it would occupy more space than 
can fairly be devoted to it were I to attempt a # 
thorough description of its somewhat anomalous' 
structures and morpho-liistological peculiarities. 
We may briefly classify its various component parts 
into two groups, those belonging to the cortical or 
outer layer, and those of the inner or woody layer. 
The line of demarcation is not clearly marked, and 
it is doubtful whether the apparently sinuous medul¬ 
lary rays may not more properly be regarded as a 
sinuous involution of the cortical parenchyma. The 
structure of the inner zone is somewhat complicated. 
There is no true medulla. There are no wood wedges 
strictly speaking. The vascular bundles are irregu¬ 
larly distributed, are large, and of varied constituents. 
I will describe them first. The vessels are pitted, 
the cells of which they are formed are not long, but 
the original membrane which formed the septa be¬ 
tween the cells has been completely absorbed, and all 
that remains to show that the vessels were once short 
cells is the somewhat unusually slight “ horizontal 
wall” of Selileiden, with a perforation nearly as large 
as the internal diameter of the vessel. The course 
Journal de Pliarmacie/ vol. [4] yii. 411. 
f Journ. Pliarm. [4] xiv. 247; and Pharm. Journ. [3] 
ii. 541. 
