The Romance of Modern Chemistry

THE ADULTERATION OF FOOD ordinary food-stuffs of the breakfast-table are not always what they seem, with the exception, perhaps, of sugar, on the purity of which one can depend. The reader may be interested to hear a little about the ways in which these foods are adulterated, and about the methods by which the fraud can be detected. In the case of milk the chief, and one might almost say the natural, adulterant is water. New milk contains as much as 87 per cent, of water, and the uninitiated might suppose that it would be very easy to add a little more without detection. Careful analysis, however, will always reveal any such manipulation, although it must be borne in mind that there may be a certain difference in the richness of milk from various cows. One method which the chemist has at his disposal is the determination of the specific gravity—that is, he finds out how much heavier the milk is than an equal bulk of water. It is worth while remembering that the first recorded determination of the specific gravity of a sub- stance was in connection with a question of fraud. Hiero, the King of Syracuse, had commissioned a goldsmith to make him a crown out of a certain quantity of gold. When the smith brought the finished crown, Hiero some- how suspected that there was an admixture of base metal, and asked Archimedes to find out for him whether this was so. The philosopher took a lump of pure gold equal in weight to the crown, and put each into a vessel full of water. He found that more water overflowed from the vessel into which the crown had been put than from the other, and concluded rightly that the crown must contain some lighter and baser metal. So the deter- mination of specific gravity as a means of detecting fraud is a time-honoured practice. 262