The Determination of Arsenic (Classic Reprint)

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Excerpt from The Determination of ArsenicThe standard stains should be of a deep orange color grading sharply into a short yellow stain and the unaltered white of the mer curio bromid paper. Zinc, sulphuric acid, hydrochloric acid, and other reagents commonly used can be purchased practically free from arsenic. Instead of stick zinc, 4 to 8 grams of granulated or moss zinc may be used, but in the use of the latter the evolution may be too rapid and cooling the generator become necessary. The stand ard paper is made from heavy, close-textured drafting paper, which is cut into strips mm by 12 cm. These strips should possess considerable stiffness to allow ready insertion in the capil lary tube. They are sensitized by soaking an hour. In 5 per cent alcoholic mercuric bromid solution, taken out (excess of solution rapidly squeezed off), separated on glass rods, and allowed to dry. They are preserved conveniently in a Mason jar.Mercuric bromid has been found far superior to mercuric chlorid for sensitizing, because of the increased permanence of the stains. No development is practiced with the former and the stains will last six months or more with but little fading, while mercuric chlorid paper undeveloped fades in a few days' time. The stains produced on either of these papers are of a dark orange color and the length of stain indicates the amount of arsenic. If the speed of hydrogen evolution 18 too rapid, the stain will be drawn out in length and at times entirely yellow. If these yellow stains from the mercuric chlorid paper are developed in ammonia, they give a gray black color indistinguishable from the developed orange stain, thereby giving the appearance of more arsenic than is present.By regulating the acidity, volume of solution, amount of zinc, and the subsequent rapidity of stain production, uniform results can be obtained.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.