PRUSSIC ACID, ANTIMONY, AND ARSENIC. 
141 
stance is very easily obtainable, is the most uniform in condition, and the 
least liable to adulteration. The quantity corresponding to the iron solution, 
in order to yield with prussic acid an equivalent of Prussian blue, is 9 equiva¬ 
lents, for there are 6 equivalents of hydrochloric acid, and 3 equivalents of 
sulphuric acid, which, therefore, in combining with the soda, gives 6 equiva¬ 
lents of chloride of sodium and 3 equivalents of sulphate of soda; and if 
there should have been a quantity of prussic acid in the stomach equal to 
9 equivalents, the whole of the iron would have been converted into Prussian 
blue ; but if the quantity of prussic acid should have been equal to 4^ equi¬ 
valents, or, say hall that quantity, the half or the quarter of the iron would 
have been changed into Prussian blue, and the remainder into protosesqui¬ 
oxide of iron, a compound which may be taken inwardly without bad effects. 
The equivalent of crystallized'carbonate of soda, not effloresced, is 143, nine 
times that quantity is 1287, and the hundredth part is consequently 12*87. 
The antidote for 2*4 grains anhydrous prussic acid, or upwards of 100 minims 
of medicinal prussic acid, is therefore theoretically 6*14 mins. liq. fern per- 
chloridi and 4*17 grs. green vitriol, mixed together in one solution, and 
another solution containing 12*87 grs. crystallized carbonate of soda. But 
we would recommend about six times these quantities for every 100 mins, 
medicinal prussic acid supposed to have been taken. We would therefore 
propose to attach to every bottle of sol. ferri perchloricli kept in stock by 
every druggist, a printed direction such as we append to this paper. For 
ourselves, we have already put into the printer’s hands such directions. 
The reason for so large an excess of the antidote to prussic acid being re¬ 
commended is, that the carbonic acid interferes with the reaction, producing 
Prussian blue. The affinities of the carbonic and prussic acids for the soda 
are so nearly balanced that the reaction resulting in Prussian blue is not com¬ 
plete without the presence of a large excess of the iron and carbonated alka¬ 
line solution. The result would be very different with the use of a caustic 
alkali, but its corrosive action and less definite state preclude its use. 
AVhen poisoning has been caused by cyanide of potassium, in which the 
prussic acid is already united to a base, the alkaline solution forming one 
part of the antidote does not, of course, require to be given, although the an¬ 
tidotal action would not be prevented by giving it in the way recommended. 
The only result that would follow giving double the proper quantity of alkali 
would be the formation of yellow prussiate of soda and protosesquioxide of 
iron by the decomposing action of the carbonate of soda on the Prussian blue 
first formed. The yellow prussiate of an alkali is known to be a compara¬ 
tively very inert substance. 
The proof of what has been said is very easy. Take the quantity of a 
solution of protosesquisalt of iron, as given for the prussic acid antidote, then 
add the equivalent quantity of a solution of cyanide of potassium, in order to 
form Prussian blue. On now adding the quantity of solution of carbonate of 
soda corresponding to the iron solution, the Prussian blue, on brisk stirring, 
loses its colour for a greenish-black of protosesquioxide of iron, and, on now 
filtering, the filtrate reproduces Prussian blue on the addition of a persalt of 
iron. 
The solution of perchloride of iron also supplies the means of obtaining in¬ 
stantaneously Bunsen’s antidote for arsenious acid. When this idea first 
occurred to us, we intended to try in what time the hydrated peroxide could 
be thrown down, washed, and got into a state [for exhibition to the patient ; 
but on reflection, it appeared quite unnecessary to spend a moment’s time 
more than would be required to measure out the quantity of solution of per¬ 
chloride of iron, mix it wilh the alkali, and, after stirring, to give it at once 
to the patient. 
