194 ANNUAL OP SCIENTIFIC DISCOVERY. 



When the plate has been immersed in the alcoholized potash during 

 half an hour, it is taken out of the solution by means of the glass hold- 

 er and immediately plunged in alkaline water, and agitated pretty 

 strongly ; from thence it is put in distilled water. (A.) 



This being done, the plate is plunged into acidulated water, and 

 moved about therein for a few seconds ; it is then put in the normal 

 acid. When the plate has been immersed a few seconds in the acid 

 it is taken out by means of the glass holder, taking care to keep it as 

 much as possible covered with the solution, and it is immediately placed 

 horizontally upon a stand, and as much acid as the plate can hold is 

 poured upon it from the bottle; it is then heated with a spirit lamp, 

 but without attaining the boiling point. During this operation it is 

 better to stir or move about the acid on the plate by pumping it, and 

 ejecting it again, by means of a pipette or glass syringe ; after two or 

 three minutes the acid is thrown away, the plate is put into the glass 

 funnel, a"nd there washed well with water, and afterwards with distilled 

 water. (B.) 



Then without letting the plate dry, it is put upon the fingers of the 

 hand, and with the right hand some ammoniacal chloride of silver, 

 which is moved about the surface by balancing the hand, is poured 

 upon it ; the solution is renewed until the chloride, formed by the ac- 

 tion of the acid, is dissolved ; the plate is then washed by pouring up- 

 on it a large quantity of ammoniacal water and afterwards some dis- 

 tilled water. (C.) 



Without allowing the plate to dry, it is then put in the caustic pot- 

 ash, and the capsula being placed upon the stand, the potash is heated 

 up to the boiling point. It is then left to cool (D.) ; and beginning 

 the operation described from A to D, a second biting is obtained ; and 

 repeating again the operations described in A and B, a third biting is 

 produced. The plate is dried : in this state the black parts of the plate 

 are filled with chloride of silver. 



The plate is then polished until the white parts are pure and bright. 

 This polishing is done with cotton and " pounce " (pumice stone) ; 

 afterwards, the chloride of silver, filling the black parts, is cleansed by 

 the means described in B and C. The plate is then dried ; but before 

 drying, it is well to rub the plate slightly with the finger, in order to 

 take off from the black parts any remains of an insoluble body which 

 generally remain on it. The preparatory engraving is then finished, 

 and the plate has the appearance of a very delicate aquatint engraved 

 plate, not very deeply bitten in. 



Nevertheless, if the operation has been well managed, and has been 

 successful, it is deep enough to allow the printing of a considerable 

 number of copies. 



Note. Sometimes, instead of treating the plate with the boiling 

 potash in the capsula, a similar result may be obtained by placing the 

 plate upon the stand, covering it with the solution, and heating it by 

 means of a spirit lamp, until, by evaporation, the potash becomes in .a 

 state of ignited fusion. By this means the grain is finer, but the white 

 parts are more liable to be attacked. 



