iS* Mr. E. Turreli's Menstruum Jin- Biting-in on Steel Plates. 



turity a process that, in its present infant state, has many great 

 and vexatious difficulties attached to it. 



Shortly after Mr. Warren made his invention known to the 

 Society, I was requested to execute some etchings on steel 

 plates ; but, previous to assenting, I thought it necessary to 

 tiy how far the menstruum of Mr. Warren's invention would 

 do for biting-iu the even tints produced by machine-ruling, 

 that being a kind of work more calculated to show the imper- 

 fection of bad biting than any other. And more particularly 

 so when three lines are used to pi'oduce those aerial tints that 

 ai'e necessary to form the back-grounds to portraits, and to 

 many other subjects, which, if produced by the graving tool, 

 would (upon steel) be enormously expensive. 



Having prepared the menstruum, according to the direc- 

 tions given, I certainly felt great difficulty in preventing a pre- 

 cipitation of the copper, which, filling the lines, continues 

 to accumulate ; and by its pressure, as it increases, removes 

 the etching-varnish jjartially from the sides of the lines, and 

 thereby causes, in a great degree, the shallowness before com- 

 plained of. 



I have no doubt, that on very small plates it may be possi- 

 ble to sweep the surface of the plate with such rapidity, that 

 this evil may in a great degree be prevented ; but upon large 

 plates, where they are covered with work, such an operation 

 will be attended with great difficulty, and in many instances 

 will be nearly impossible. 



In biting-in on copper plates, the breadth of the etched line 

 is in a great degree indicated by the size of the bubble of ni- 

 trous gas formed on the line; but where the lines are filled 

 or covered with the precipitated copper, the difficulty of judg- 

 ing of the state of the biting is greatly increased. 



These and other difficulties incited me to give the subject 

 every attention in my power. The first indispensable requisite 

 (as it appeared to me) was to determine what acid would most 

 readily corrode the lines etched upon the steel plate; and, 

 after trying a number, nitric acid, reduced to a proper strength 

 by dilution, appeared to me the best adapted to this purpose, 

 provided some means could be found of preventing it from de- 

 positing the oxide of iron after having taken it up. 



Chemists well know that iron exists in two states of oxida- 

 tion, the protoxide and peroxide, and that each of these oxides 

 will combine with acids forming two genera of ferruginous 

 salts, the proto-salts and the per-salts. The proto-salts con- 

 tain a larger jiroportion of oxide than the soluble per-salts ; 

 and being liable to pass into this latter state by long keeping, 



or 



