Mr, E. Turrell's Menstruum for hitmg-in on Steel Plates. ¥25 



or in a sliort time when exposed to the air, their solutions will 

 sooner or later become turbid, and will deposit peroxide of 

 iron in a state scarcely at all soluble, except by being digested 

 in hot acid, combined with some deoxidating substance. 



For this reason it is that the action of nitric acid diluted with 

 water will seldom give satisfactory results when employed for 

 biting-in ; for although at first it acts very well, the iron being 

 brought merely to the state of protoxide, and dissolving freely 

 in the acid, — yet by exposure to the air, during the process of 

 biting, it passes to the state of peroxide, a portion of which 

 precipitates, and, faUing into the lines of the etching, covers 

 the surface of the steel at the bottom of these lines, and thereby 

 impedes and renders irregular the action of the acid. 



Knowing that calico-printers prefer making their solution 

 of oxide of iron in pyroligneous acid, I conceived that, when 

 in its pure state, this would be a very proper fluid to dilute the 

 nitric acid with; because it would not only tend to reduce its 

 action, but might prevent, or at least impede the jirecipitation 

 of the oxide formed in the operation of biting. Although, 

 however, something was gained by this addition, yet it did not 

 appear to be so effectual upon repeated trials as to leave me 

 completely satisfied It then came into my mind that alcohol, 

 and, still more, ether, have a very powerful deoxidating ef- 

 fect, as they are able to separate gold, in its pure metallic 

 state, from its solution in aqua regia. I determined, therefore, 

 upon adding to the n)ixture of pyroligneous and nitric acids a 

 portion of alcohol, expecting that the nitrous ether resulting 

 from this combination being presented in its nascent state to 

 the nitrate of iron formed during the biting, would retain it in 

 the state of proto-nitrate, and thus prevent any precipitation. 

 I am happy to say I was not in the least disappointed ; for 

 with a menstruum thus formed or compounded of the three 

 ingredients, namely, pyroligneous acid, alcohol, and nitric 

 acid, I acfjuire the following advantages. 



In the first place, it corrodes the steel with great facility, 

 producing a beautiful, clear, and deep line ; and upon a va- 

 riety of plates the results were very uniform. 



Secondly, it prevents the deposition of peroxide ; as a proof 

 of which I have kept some of the menstruum which had been 

 employed for biting-in as long as six months, and could not 

 discover any precipitation Ibrnied. 



As a furtiier ))r<)of ol' its power of holding the oxide formed 

 in j)erfecl solution, it will be distinctly seen (hat as soon as the 

 corrosion takes jjlace upon the steel plate, the whole of the 

 lines appear beautifully bright, and cojitinue so until the biting- 

 in is completed. 



Vol. fifj. No. 326. June 1825. 3 H The 



