The essential points of this process, which constitute the present invention, consist,—
First,—in the discovery and employment of certain properties of a mixture composed of nitric acid, nitrous acid, and hydrochloric acid, in detrimental or fixed proportions. The two last mentioned acids may be employed either in a free state, or combined with alkaline or other bases. This mixed acid has the property of biting the pure silver, which forms the black parts of the Daguerreotype picture, without attacking the white parts formed by the amalgam of mercury.
The result of the action of the biting is, to form on the black part of the picture an insoluble chloride of silver; and this chloride of silver, which, when formed, stops the action of the acid, is dissolved by the ammonia, which allows the biting to continue.
Secondly,—In the discovery of certain properties of a warm solution of caustic potash, and in the employment of the said solution, by which the mercury forming the picture is better and deeper amalgamated with the silver under it, so that many imperceptible points of the amalgam are affected in such a manner that the action has no action upon them.
Thirdly,—In the discovery and employment of a process which produces a grain favourable to the engraving, by which the biting on the plate is rendered deeper. This is effected by filling the parts engraved with a siccative ink, or any other substance, and then gilding the plate by the electrotype process: the gold is not deposited on the parts protected by the ink. When the plate is gilded, the ink is cleansed by the caustic potash, and the plate may be submitted to the effect of an acid, which does not attack the coating of gold, but bites only on the silver in the parts already engraved by the first operation.
Fourthly,—In the employment of a process by which the plate is protected from the wear of the printing operation. This is effected by covering the plate before printing, with a slight coating of copper; by the electrotype process, and when the coating begins to wear, by printing, it is removed by a weak acid or by ammonia, which dissolves the copper without effecting the silver under it. The plate is coppered again, and after another printing, the same operation is repeated, so that a considerable number of copies may be printed without injury to the engraving.
Enrolled in the Pitty Bag Office, May, 1844.
[INTERESTING EXPERIMENT WITH STRYCHNIA.]
An interesting experiment, illustrative of the poisonous effects of strychnia, was recently made by Professor Agassiz, at Cambridge. The subject was a large black bear, about eighteen months old. The animal was taken when young, and had been kept in captivity for a considerable period. Professor Agassiz being desirous of killing it for the purpose of dissection, about three grains of strychnia were administered. The poison, though extremely bitter was readily swallowed. At the expiration of ten minutes, no effect having been produced, a second dose of about the same quantity was also inclosed in a biscuit and offered. The cunning animal broke open and swallowed the biscuit, but rejected the poison. The first portion, however, had proved efficacious, and in exactly fifteen minutes from the time when first administered, the animal was seized with terrible convulsions, and soon died.