Legal Chemistry / A Guide to the Detection of Poisons, Examination of Tea, Stains, Etc., as Applied to Chemical Jurisprudence

by Alfred Naquet

DETECTION OF CHLORINE, BROMINE, AND IODINE.

CHLORINE AND BLEACHING CHLORIDES.

The detection of chlorine is very difficult owing to the great tendency it possesses to become converted into chlorides or hydrochloric acid, and it is only when found in a free state that its discovery is of importance.

In case the gas exists uncombined in the alimentary canal, its odor will be perceptible, and, upon boiling the suspected materials with water, vapors will be evolved which impart a blue color to paper saturated with a mixture of iodide of potassium and starch paste. If the addition of sulphuric acid is necessary in order to produce the above reactions, there is reason to suspect the presence of "chloride of lime" or "Eau de Javelle."[J]

BROMINE.

In case bromine exists in a free state at the time the autopsy is made, its presence will be detected by the reddish color and unpleasant odor it possesses. Its isolation is accomplished by treating the materials with bisulphide of carbon which, upon dissolving the bromine, acquires a red color. If potassa is then added to the solution, it combines with the bromine and, upon evaporating the decanted fluid, calcining the residue, and treating it with water, a solution of bromide of potassium is obtained. Upon adding chlorine-water and ether to a portion of the fluid, and shaking the mixture, the bromine is liberated and is dissolved by the ether. The etherial solution of bromine, which possesses a reddish-yellow color, does not mingle with, but floats upon the surface of the colorless aqueous solution.

If nitrate of silver is added to another portion of the aqueous solution of bromide of potassium, a precipitate of bromide of silver, soluble in ammonia, is formed.

In case the bromine has been converted into a bromide, it is necessary to boil the alimentary canal and the articles of food contained therein with water. The fluid is next filtered and agitated with chlorine-water and ether. The liberated bromine is dissolved by the ether, which acquires a reddish-yellow color. Upon decanting the solution, and treating it with potassa, bromide of potassium is formed, and can be detected as directed above.

IODINE.

The detection of iodine is accomplished by a process almost identical with the above. The isolation of the iodine having been effected, it remains to be ascertained that it imparts a blue color to starch paste, and a violet color to bisulphide of carbon.