been made sufficiently full, and clear enough, it is hoped, for the most inexperienced analyst. Additional skill and valuable experience are acquired with each trial, so that, when the section treating of separations is reached, the work there outlined will be performed without difficulty. Before commencing the determination of any one metal read, if possible, its literature. The methods of determination and separation given preference are not those of any one individual, but have been selected from all sources after an experience of many years, care being taken to present only those which actual tests have shown to be reliable and trustworthy. It has not been considered advisable to include an outlined electrolytic analysis of alloys and minerals in the text, inasmuch as the experience gained in performing the analyses already described there will have given the analyst such a fund of experience that the course to be pursued in special cases will readily suggest itself. The author would here acknowledge his indebtedness to the various writers on electrolysis, whose publications he has freely used, to the editors of the different journals consulted, to friends who have made kindly suggestions, and to his brother, Dr. Allen J. Smith, who prepared all the drawings from which the illustrations of the text were made. University of Penna., Philadelphia, Sept., 1890. S. TABLE OF CONTENTS. PAGE Grenet Battery, Leclanché Cell, Daniell Cell, Meidinger ELECTRO-CHEMICAL ANALYSIS. INTRODUCTION. Many chemical compounds are decomposed when exposed to the action of an electric current. A decomposition of this kind is called electrolysis, while the substance undergoing change is termed an electrolyte. The products of the decomposition are the anions and cathions, or those (1) which separate at the anode, the positive electrode or pole (+ P) of the battery, and (2) those separating at the cathode, the negative electrode or pole (— P) of the battery. This behavior of compounds has become of great service to the analyst, inasmuch as it has enabled him to effect the isolation of metals from their solutions, and by carefully studying the electrolytic behavior of salts it has been possible for him to bring about quantitative determinations and separations. The electrolytic method of analysis is especially inviting, since it permits of clean, accurate and rapid determinations where the ordinary methods yield unsatisfactory results. This statement is readily confirmed on recalling the gravimetric methods usually employed in the estimation of copper, mercury, cadmium, bismuth, tin, etc., etc. That this assertion may be the conviction of every student of analysis, the writer would call attention first to the course of the current in solutions of some of the more frequently occurring salts; after which will follow a brief account of the various modes of obtaining the electric current, how it may be measured and how controlled. Finally, all the metals, which have been studied electrolytically, will be taken up in detail, and their various determinations will be followed by a sufficient number of separations to show, at least in part, how widely the electrolytic method of analysis may be applied. I. ACTION OF THE ELECTRIC CURRENT UPON ACIDS AND SALTS. In this last case the hydrogen further acts upon more nitric acid and produces ammonia (NH3) and water. Lead nitrate + the current Pb+ NO2+0. The oxygen liberated here attacks a second molecule of |