CAVEAT EMPTOR is a good maxim, if a somewhat hackneyed quotation. The principle it embodies need not be disregarded, even by the chemist. True, he is a protector of the purchasing public in certain cases where that public cannot take care of itself; but this does not absolve him from the necessity of keeping a watchful eye upon his own purchases. On the contrary, the very fact that he may be called upon, for instance, to certify to the purity of other people's food makes it all the more incumbent upon him to look well after the purity of his own reagents. It may happen—and it has happened—that through insufficient attention to the quality of his chemicals, an analyst may introduce into some article the very impurity which he is required to search for, or an investigator in pure chemistry may be led to propound some brilliant theory which more circumspect working presently renders untenable. As examples in point, one need only recall the testing of foodstuffs for arsenic, and the alleged conversion of this element into antimony. Wherefore, when the chemist buys his chemicals let him remember the legal tag above quoted, and not trust too implicitly to the manufacturer who supplies them. The Testing of Chemical Reagents for Purity. By Dr. C. Krauch. Third Edition. Authorised translation by J. A. Williamson, F.C.S., and L. W. Dupre. Pp. 350. (London: Maclaren and Sons, n.d.) Price 12s. 6d. net.