grm. manganese.  On electrolyzing a manganiferous solution of copper nitrate, red permanganic acid appeared in a stratum floating above the platinum disk coated with brown peroxide.  No manganese peroxide was deposited.  The peroxide adheres firmly to the platinum when the proportion of free acid is small, not exceeding 3 per cent., and the current is not too strong.  If the action of the current is prolonged after the peroxide is thrown down, it falls off in laminae.  According to Riche, in a nitric solution the manganese is deposited as peroxide, also at the negative pole.  This formation is not directly due to the current, but is a precipitate occasioned by the production of ammonia by the reduction of nitric acid.  To determine the manganese in peroxide electrolytically precipitated, it is heated to bright redness in the platinum capsule until the weight becomes constant.  The results are too high.

Selenium and Tellurium.—­Both these bodies are readily and completely reduced by the current either in acid or alkaline solutions.  Selenium is thrown down at first of a fine brownish red, which gradually becomes darker.  The deposit of tellurium is of a bluish black color.  If the current is feeble, the deposit of selenium is moderately compact; that of tellurium is always loose, and it often floats on the liquid.  A strong current precipitates both as powders.  The positive pole is coated during electrolysis with a film of a dark color in case of selenium, but of a lemon yellow with tellurium.  As in case of arsenic and antimony, the hydrogen evolved at the negative pole combines with the reduced substances, forming hydrogen, selenide, or telluride, which remain in part in solution in the liquid.  The reduced metal separates out at the anode in a friable condition.—­Zeitschrift fur Analytische Chemie, and Chemical News.

* * * * *

THE ELECTRO-CHEMICAL EQUIVALENT OF SILVER.

A very careful and important determination of the electrochemical equivalent of silver has been made at the observatory of the Physical Institute of Wuerzbourg, and the results are that an ampere current flowing for a second, or a coulomb of electricity deposits 1.1183 milligrammes of silver or 0.3281 milligramme of copper, and decomposes 0.09328 milligramme of water, a result agreeing closely with that of Lord Rayleigh recently communicated to the Physical Society.  An ampere therefore deposits 4.0259 grammes of silver per hour; Kohlrausch’s value is 4.0824, a value hitherto accepted universally.  This value is so useful in measuring electric currents with accuracy, and free from the disturbances of magnetism, etc., that it is eminently satisfactory to find the German value agree with that of Lord Rayleigh, which will probably be adopted by English electricians.

* * * * *

A NEW STANDARD LIGHT.