Thallium behaves similarly to lead. From a nitric acid solution it is thrown down, according to the proportion of free acid, either as sesquioxide only or in small quantities as silvery, metallic leaflets; from alkaline solutions it is deposited as sesquioxide and metal, the latter of a lead-gray color. Thallium solutions conduct the electric current badly. Thallium oxide resembles lead peroxide in color; at a strong heat it melts, becomes darker, and is converted into peroxide, in which state it can be weighed.

Silver

All solutions of silver salts, except the nitrate, and those containing a very large quantity of free nitric acid or nitrates, deposit electrolytically merely metallic silver. In the above mentioned exceptional cases there is formed a small quantity of peroxide which adheres to the anode as a blackish-gray deposit. The greatest quantity of peroxide is obtained on employing a concentrated, strongly acid solution of the nitrate, and a strong current. If the solution is very dilute we obtain no peroxide, or mere traces which disappear again toward the end of the process. The peroxide is deposited at first in small, dark, shining octahedral crystals; subsequently, in an amorphous state. At 110° it evolves oxygen suddenly, and is converted into metallic silver. It dissolves in ammonia with a violent escape of nitrogen. In nitric acid it dissolves without decomposition and with a red color.

The author uses a galvanic current for reducing silver residues, consisting of sulphocyanide. The salt is mixed with sulphuric acid in a roomy platinum capsule, and a fine platinum wire gauze is used as positive electrode.

Bismuth

The current resolves bismuth solutions into metal and bismutic acid. The latter is deposited at the positive pole, and in thin layers appears of a golden-yellow, but in thick strata is darker, approaching to red. Its formation is very gradual, and in time it disappears again, owing to secondary actions of the current. On ignition it becomes lemon yellow, and transitorily darker, even brown, and passes into the sexquioxide.

Nickel And Cobalt

On the electrolysis of the ammonical solution the sesquioxide appears at the positive pole. Its formation is prevented by an excess of ammonia. The author never obtains more than 3½ per cent. of the quantity of the metal. The sesquioxides dissolve in ammonia without escape of nitrogen, and are usually anhydrous.

Manganese

Manganese is the only metal which is precipitated only as peroxide. It is deposited at once on closing the circuit, and is at first brown, then black and shining. Organic acids, ferrous oxide, chromic oxide, ammonium salts, etc., prevent the formation of peroxide and the red color produced by permanganic acid. In very dilute strongly acid nitric solutions there is formed only permanganic acid, which according to Riche is plainly visible in solutions containing 1/1000000 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 Würzbourg, 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.