532 Intelligence and Miscellaneous Articles. 



almost invariably require to be touched up afterwards, and therefore 

 absolute identity is destroyed. The cost of their manufacture would 

 be trifling, being merely the value of the zinc* dissolved in the bat- 

 tery, and a pound of zinc of the value of sixpence would produce a 

 copper-plate weighing about two pounds ; and I trust that copper 

 will again, from its beauty, take the place of steel engravings. 



So much for the precipitation of the copper ; and the next thing 

 to which I have to direct your attention, is a mode of making a copper- 

 plate engraving without an engraving in the first instance. This is 

 done by drawing upon a smooth piece of copper (such as a plate 

 used for engraving) with any thick varnish or pigment insoluble 

 in water, and then exposing the plate in the usual way to the in- 

 fluence of the current, when first copper will be thrown down upon 

 the uncovered parts and will gradually grow over the drawing, and 

 the electrotype when removed will be ready for printing, A pra ctical 

 difficulty, however, arises in the application of this in the arts, t or un- 

 less very thic k oil paint is used, sufficient depth is not obtained to hold 

 the ink . Howe ver, iudging; from the sharpness of theedgesof the lines, 

 1 have but ht tie doubt t hat this difficulty may be overcome by these 

 who are accustomed to drawing ; and it possesses, as an additional 

 advantage to its cheapness, the valuable property of not requiring 

 the artist to reverse the design. An opposite effect to this may be 

 l)roduced by placing a piece of copper similarly drawn upon at the 

 oxygen end of the battery, when the metal will be acted upon, lea- 

 ving a drawing in basso relievo. 



Bank of England, April 21, 1840. 



ON THE REDUCTION OF CHROMATE OF LEAD. BY R. F. MAR- 



CHAND. 



The employment of chromate of lead, instead of oxide of copper, 

 in organic analysis, is in many cases recommended by Richardson. 

 It is preferable in the examination of substances containing chlorine, 

 iodine, bromine, and sulphur, but particularly in the examination of 

 the two latter. Erdman and I have frequently employed it with 

 Hess's apparatus, and observed that the reduced chromate of lead 

 will again absorb oxygen and might be then again employed. This 

 circumstance induced me to make various experiments upon the 

 reduction of this salt. 



The chromate of lead used in these experiments was prepared by 

 the precipitation of a solution of nitrate of lead with an excess of 

 bichromate of potash, and afterwards carefully washing it : the salt 

 was heated to dryness ; it became of a dark red colour approaching 

 cinnabar red ; on cooling it returned to its former yellow colour 

 provided it was not fused. If fused it turned to a dark brown co- 

 lour, which on reducing to powder was of a brownish yellow colour. 

 When the fused salt is quickly cooled by throwing it into cold water 

 it becomes of a permanent red colour, giving also a red j)owder. 



* The zinc in the fluid might be precipitated as a carbonate, for which 

 there is great demand in the arts, and thereby the expense of the electro- 

 type would be further diminished. 



