A SECOND, revised, and enlarged edition of “The B.D.H. Book of A.R. Standards” has been issued (price 28. 6d. net; postage 6d. extra) by the British Drug Houses, Ltd., Graham St., City Road, London, N.I. Fifty new substances have been added to the 158 chemicals in the first edition, and the limiting values of the various tests have been stated at the head of each section in the form of a table which represents the maximum permissible limits for the various impurities. We may remind readers of NATURE that the letters A.R. (replacing the unsatisfactory description “Chemically Pure” , or C.P., an unattainable ideal) denote analytical reagents of controlled and specified purity, and users of such reagents will thus be able, by means of this monograph, to judge what impurities may possibly be present and in what amounts. It is clear that, with improvement in analytical chemistry, some of the specifications may be given still further precision in future editions. The entry under copper oxide, for example, on p. 62, which returns nitrate, carbonate, and organic matter as “nil” on the basis of a rather crude test, is obviously capable of revision, and other cases will no doubt suggest themselves to the reader. For routine work, as distinguished from research, these specifications will be of considerable value, and the book will be found useful in all analytical laboratories.