A A NEW HYDROGEN-ION POTENTIOMETER As the first of several new instruments of interest to the scientific worker, Leeds & Northrup Company takes pleasure in announcing a new Portable Potentiometer for Hydrogen-Ion Measurements. It is a potentiometer-an instrument that owes its accuracy to the great accuracy and constancy of a standard cell and of electrical resistances. It does not merely employ a compensation method. The Portable H-Ion Potentiometer is not only useful in laboratory work, but it will generally find a place in plant and field surveys, and wherever portability in such a set is a desirable feature. Standard cell, galvanometer, adjusting rheostat-all are enclosed in a substantial oak case 6" x 6" x 91⁄2", provided with a carrying strap. All parts are ruggedly constructed to withstand hard usage. The usual L. & N. guarantee applies to this potentiometer, as it does to all of our instruments. There are two models. Both are exactly alike in size and external appearance, and both have the same range. No. 7655 has a main dial and slide wire, and measures accurately to±0.5 millivolt (1% of a pH unit). No. 7656, with slide wire only, is accurate within 5 millivolts (10% of a pH unit). Several No. 7655 potentiometers are in stock. PRICES 7655 L. & N. Portable Hydrogen Ion Potentiometer, range o to 1200 millivolts, INSTRUCTIONS FOR OPERATING 7656 L. & N. Portable Hydrogen Ion Poten- . $150.00 $120.00 LEEDS & NORTHRUP COMPANY Electrical Measuring Instruments 4901 Stenton Avenue PHILADELPHIA, PENNA. Have you seen our catalogue S75, entitled, "Electrometric Methods and Apparatus for Determining Hydrogen Ion Concentrations"? If not, we should like to send you a copy. DIFCO RARE SUGARS and OTHER FINE CHEMICALS "DIFCO" STANDARDIZED Being the first manufacturing firm in the United States to make and advertise extensively rare sugars, we have steadily added to the line, and our list now comprises the following: OTHER CHEMICALS Mannose Melezitose Raffinose Rhamnose Fibrin Saccharose (Sucrose) Gelatin Trehalose Xylose Invertase Hemoglobin SPECIFY "DIFCO". WE INVITE COMPARISON Descriptive literature and prices upon request Carried in stock by the principal dealers in Scientific Supplies Digestive Ferments Company Detroit, Michigan, U. S. A. Repeated object lessons have demonstrated that nearly all progress in science has resulted in important advances in industry G-E Research Laboratory Schenectady, N. Y. Among the many products developed by the General For further information address Supply Department, Schenectady Office. General Electric General Office Company Second Edition, Enlarged and Completely Rewritten A DICTIONARY OF CHEMICAL SOLUBILITI (INORGANIC) By ARTHUR M. COMEY and DOROTHY A. HAHN, Professor of Che try at Mt. Holyoke College. Cloth, Octavo, 1141 pages, $14.00. The new edition of this work is in every way the most complete dictio of inorganic chemical solubilities. The solubility of each substance in wat given first; then follow the specific gravities of the aqueous solutions, the regarding their boiling points; then the solubility in the inorganic acids, i kali and salt solutions, and, finally, in organic substances. Where more one result has been obtained, data from all original authorities are cited. the material retained from the earlier edition the authors have added an e amount of new data drawn from chemical periodicals of the last twenty y covering the entire field of inorganic substances. The arrangement in dic ary form follows the plan of the first edition, the single alphabetical adapting the work to ready reference. THE MACMILLAN COMPANY PUBLISHERS NEW Y Just Published by Macmillan PHYSIOLOGY OF FARM ANIMALS By T. B. WOOD, M.A., F.R.S. AND F. H. A. MARSHALL, Sc.D. PART I. GENERAL. By F. H. A. MARSHALL. This is a most useful manual which should be of interest to studen agriculture, veterinary students, breeders, and up-to-date farmers who d some knowledge of the simpler physiological processes as they occur in animals. It gives clearly, with numerous illustrations, descriptions of the f and functions of the various organs of domestic animals, describes com diseases and malformations, and explains some of the simpler treatments operations. CONTENTS-Introduction-Histology-The Digestive Organs-The Blood and the Organs of tion-The Respiratory Organs-The Excretory Organs-The Functions of the Skin-The Nervo tem-The Organs of Special Sense-The Organs of Locomotion-The Ductless Glands and the of Internal Secretion-The Male Generative Organs-The Female Generative Organs and the Ma Glands-Index. With 105 Illustrations. $5.00. PART II. ON ANIMAL NUTRITION. By PROFESSOR WOOD, published later. The Macmillan Company, Publishers, 64-66 Fifth Ave., New Y |