(2944) Adulteration of paint.

Manufacturer and builder 2, 1882

— The material used for adulterating paints are numerous, and to give directions for detecting them all would demand an extensive article, and to apply the tests properly would also require considerable skill in chemical manipulation and imply likewise some knowledge of chemistry. We will give, however, a brief description of a practical method of determining the commonest adulterants of linseed oil and white lead, which may be of use to this inquirer. If the paint is already mixed, dissolve out the oil from a small quantity of the paint with a mixture of alcohol and ether. Evaporate off the ether, when the oil will commence to separate in oily globules. When this separation becomes pronounced, add water to the alcoholic solution. If a deuce white, milky coloration ensues on the addition of the water, the linseed oil is adulterated with the cheaper and very common adulterant known as "rosin" oil. As to the coloring matter, treat this with dilute nitric acid (aqua-fortis) in a porcelain dish with the aid of gentle heat. Pour off the liquid when the action of the acid has ceased, and if no residuum is left the color is most likely pure. If, on the other hand, a residuum is left, treat it with another portion of nitric acid as before, to make sure that enough acid has been added to dissolve all the soluble portion, and pour off the supernatent liquid. If after this second treatment any residuum is left, the white lead his been adultery. The commonest adulterant is sulphate of barytes—heavy spar, which would be left behind in the above treatment. By weighing the material before treatment, and the residuum, the per-centage of adulteration can be told. This procedure applies only to white paint (zinc or lead); with colored paints it would be worthless. If any importance attaches to the cave named by this inquirer, we would not advice him to trust to his skill in detecting the existence of a possible fraud, but to place the work in the hands of an analytical chemist, with indructione to investigate the materials and report.

Ei kommentteja :