212 ANNUAL OF SCIENTIFIC DISCOVERT. 



six hundred and fifty parts of distilled water; filter, protected from the air 

 as much as possible, and put in a closely stopped bottle until the moment 

 of usin. 



Liquor No. 2. Dissolve twenty pints of nitrate of_silver in twenty parts 

 solution of ammonia, and add to this solution six hundred and fifty parts of 

 distilled water. 



The two preceding liquors are mixed in equal quantities, and, after having 

 been well agitated, are filtered. 



As the solution of ammonia of commerce has not always the same degree 

 of concentration, it would be better, perhaps, to dissolve the nitrate of silver 

 destined for the liquor No. 2, first in distilled water, then mix this solution 

 with liquor Xo. 1, and only then add ammonia in quantity sufficient to entirely 

 clear the mixture, taking care always not to maintain an excess greater than 

 is necessary to prevent the silver from being precipitated. 



Suppose it is intended to silver silk, cotton, woollen, etc., we commence by 

 washing the substance clean; this done, we immerse it for a moment in the 

 saturated solution of gallic acid; then withdraw it to plunge it for a second 

 in another solution composed of twenty parts of nitrate of silver to one 

 thousand parts of distilled water. These alternate immersions are continued, 

 until the substance, from being dark, becomes of a brilliant tint; after which 

 it is plunged in a bath composed of a mixture of the two liquors, Nos. 1 and 

 2. When it is completely silvered it is withdrawn, and boiled in a solution in 

 water of a salt of tartar, and there remains nothing more to be done but a 

 last washing and drying. 



Stucco and pottery ought, before being submitted to the operation, to be 

 covered with a coat of stearin or varnish. 



The silvered surfaces are then washed with distilled water, dried by free air 

 and heat, and in the last place, covered with a layer of varnish. The deposi- 

 tion of silver can be accelerated by the employment of heat; in this case the 

 temperature depends upon the nature of the objects to be submitted to the 

 operation. 



As for the metals, we commence by cleaning them with nitric acid; rub 

 them afterwards with a mixture of cyanide of potassium and powdered sil- 

 ver; then, after washing with water, they are plunged alternately into liquors 

 Nos. 1 and 2, until they appear sufficiently silvered. If working with iron, 

 it should be first immersed in a solution of sulphate of copper. Jour, de 

 Chim. Med. 



OX THE THEORY OF DYEING. 



The following is an abstract of an article on the above subject, by Professor 

 Bolley, of Zurich, Switzerland, published in the L. E. and D. Philosophical 

 Magazine, for December, 1859 : 



Two questions have long been agitated among chemists interested in the 

 theory of dyeing. 1. In what part of the colored fibre is the coloring mat- 

 ter situated ? Does it merely adhere to the surface, or does it penetrate the 

 entire substance of the cell-walls of such fibres as cotton and flax? Or, lastly, 

 in the case of such fibres, is it stored up in- the interior of the cells ? 2. What 

 is the nature of the union between the dye and the fibre? Is it a chemical 

 combination, or is it due to mere surface attraction? After comparing the 

 various theories which have been advanced during the last century and dis- 

 cussing the merits of each, the author records the results of his own experi- 

 ments, from which it appears that wool and silk, in all cases where they have 



