A CONVENIENT METHOD FOR TESTING THE STRENGTH OF HYDROGEN PEROXIDE MARGARBT HAIGHT, NEWYORKUNIVERSITY, NEWYORKCITY Although hydrogen peroxide has lost some of its old time prestige as an integral part of the family medicine chest it has rather gained in favor as a bleach for animal fibers and human hair. In this capacity it is saf& efficient, and harmless if properly used. Since the value of peroxide lies in its ability to decompose, giving up its oxygen, i t is important to know how much oxygen really is available. How many people have discovered that their peroxide was practically nothing b u t water! And yet there on the label was the assertion that this was 3% 10-volume peroxide (or in the dye industry 17-volume). Incidentally, the percentage indicates the amount of pure, sirupy hydrogen peroxide liquid in 100 parts of water solution. The volume content indicates the available oxygen. One cubic centimeter of a 3% solution is capable of giving up 10 cc. of oxygen. One cc. of 17-volume peroxide is capable of giving up 17 cc. 7of oTygen. How then can we tell whether the oxygen really*is available or has escaped from the solution? A very simple device has been arranged, making use of the fact that peroxide is rapidly decomposed by alkalies and mineral salts. A fermentation tube with the closed arm graduated in cc. is filled with a strongly ammoniacal copper sulfate solution. A pipet, preferably with a curved tip, calibrated to 1 cc. as shown, is then filled with the peroxide solution in question, the outside wiped dry, and the tip inserted into the closed arm of the fermentation tube. One cc. of the peroxide solution is allowed to flow very slowly into the copper sulfate solution where it is immediately decomposed. The oxygen liberated rises in the closed arm and the volume may be read directly from the graduations on the tube. The same ammoniacal copper sulfate may be used for a great many tests since the small amount of water added from the peroxide solution does not impair its efficiency to any appreciable extent.
