NATUKAL PHILOSOPHY. 187 



face, is either to produce an incipient crystallization of the silver, which is 

 afterward continued by the mercury, or else it in some way promotes the 

 susceptibility to being crystallized by the mercury. It is well knowTi that 

 the action of mercury in small quantities on a metal is to crystallize it. In 

 some of the metals its action is so energetic that the mass is severed by the 

 new arrangement of the metal. That it is the crystallization which deter- 

 mines the action of the solvents to the design, will appear from the well- 

 known fact that crystallization resists the action of solvents, and also that 

 the plate is bitten all over ; most in the deepest shades least in the brightest 

 lights. If the mercury acted as a protecting film, the action would spread 

 under the lights and cut-lines, wider at the bottom than at the top, and leave 

 the lights smooth and flat, and terminating abruptly. But any person who 

 will take the trouble to etch a Daguerreotype, will soon perceive that the 

 edges of the lights are rounded off, and the lines are wider at the top than in 

 the bottom. The crystallization in the Daguerreotype goes down deep into the 

 metal ; it also extends itself under the shades, or laterally, from where the 

 mercury has deposited. Is~ow, the consequence of this spreading of the crys- 

 tallization under the shades is, that the lines [whites?] of the etching are, in 

 the beginning, somewhat narrower than hi the Daguerreotype or in the draw- 

 ing. Here is a provision against the spread of the lines, in deepening into 

 the copper. 



^'TVith the smoothness of the bottom of the wide lines I shall not trouble 

 myself yet awhile. The electrotype process must necessarily be employed 

 for forming the plates ; by no other means can metal of absolutely uniform 

 texture be made. But the electrotype gives us the means of entering a plate 

 at any desirable part, and altering its contexture ; and this is giving us the 

 means of making the solvent bite what is called a " grain" at any desk-able 

 depth from the surface. Suppose, after the plate has been formed to the 

 thickness of an hundredth of an inch, it be taken from the electrotype 

 apparatus and dusted over with powder of silver, and then returned to tho 

 apparatus and completed in thickness, would not the solvent, in biting down 

 from the face of such a plate be resisted by the particles of silver, and thus 

 form a very rugged surface ?" 



NEW PROCESS FOE EXGEAYIXG OX ZINC. 



M. Dumont, an engraver of Paris, describes, under the name of Zincography, 

 a process for electric engraving, which is promising. Upon a thick plate of 

 zinc, planed and grained with a steel tool and fine sand, he draws any subject 

 with a kind of lithographic crayon ; upon the design, when finished, he sprin- 

 kles a fine powder, mixed with resin, Burgundy pitch, and bitumen of Judea; 

 by heating the zinc plate he melts this powder, which is converted into a 

 varnish, and spreads over the parts of the surface which have been covered 

 with fat crayon, that is, on every thing which constitutes the design. To bite 

 'in the plate, and obtain the design in relief, he plunges it, while in connection 

 with the positive pole of the pile, into a bath of sulphate of zinc, in face of 

 another plate connected with the negative pole ; the current passes and cor- 



