[140] “Merkbuch,” p. 68.
[141] Instead of calcium chloride strong sulphuric acid may be used for dehydration, but the dry chloride is more simple, and less dangerous. If kept in corked bottles, the corks should be covered with paraffin wax to prevent access of moisture.
[142] First put forward by Chevreul (see pp. [22] and [117]).
[143] [The so-called ‘pole paper’ is supplied by most dealers in electrical apparatus. Transl.]
[144] In such a case the hydrated oxide of tin is either present as such in the oxidized bronze, or it is a product of the reduction which has been prevented from falling to the bottom by the high sp. gr. of the potassium cyanide solution. It is also possible that finely divided tin in the reduced bronze may decompose the warm water into oxygen and hydrogen, forming a hydrated oxide of tin. Such a reaction would account for the formation of hydrogen. The hydrogen might at the same time remain occluded until allowed to separate by the cessation of the current and the temperature of the water.
[145] Such, for instance, as is obtained by attaching a suitable nozzle to a fall pipe where there is sufficient water-pressure; v. e.g. “Polytechn. Centralblatt,” 1891-92, p. 199.
[146] I now consider it a better plan not to employ the method of coating with paraffin wax. I thoroughly soak and then dry the reduced bronze with a cloth, and place it in 96% alcohol. This must be renewed after a time, and for large bronzes a third or even a fourth renewal is advisable. The bronze is again wiped and introduced into a drying oven raised to about 212°F. [100°C.]. The unsightly grey colour and rough surface may be much improved by using a brush of the finest wire or very fine emery cloth. The object is finally impregnated with zapon (see Appendix). (Author’s note, 1904.)
[147] [The base was not treated owing to the advanced destruction of the metal. Transl.]
[148] In only about 2% of the bronzes treated in the laboratory of the Royal Museums at Berlin has it been found necessary to interrupt the reduction.
[149] “Polytechn. Centralblatt,” 1891-92, p. 200.