Page:The British pharmacopœia.djvu/525

Rh In each case, excepting that of iodum, a solution of iodide of potassium and hydrochloric acid are added to the substance, and the amount of iodine so liberated is indicated by this solution.

VOLUMETRIC SOLUTION OF IODINE.

(Iodine, 1 = 127.)

Take of Put the iodide of potassium and the iodine into the 10,000 grain flask, fill the flask to about two-thirds its bulk with distilled water, gently agitate until solution is complete, and then dilute the solution with more water until it has the exact volume of 10,000 grain-measures. 1,000 grain-measures of this solution contain $1⁄10$ th of an atomic weight in grains (12.7 grains) of iodine, and therefore correspond to 1.7 grain of sulphuretted hydrogen, 3.2 grains of sulphurous anhydride, and 4.95 grains of arsenious anhydride.

Grammes and cubic centimetres may be employed instead of grains and gram-measures, but for convenience $1⁄10$ of the numbers should be taken. 100 cubic centimetres contain 1.27 gramme of iodine, and correspond to 0.17 gramme of sulphuretted hydrogen, 0.32 gramme of sulphurous anhydride, and 0.495 gramme of arsenious anhydride.

This solution is used for testing the following substances. It is dropped from the burette into the liquid to be tested until free iodine begins to appear in the solution.