36 ANNUAL OF SCIENTIFIC DISCOVERY. 



ing. Specimens of emeraldine, a new green, and azurine, a new 

 blue, were exhibited by Mr. Grace Calvert. Of these, emeraldine is 

 produced by preparing cotton with chlorate of potash, and then print- 

 ing with an acid chloride of aniline ; in a given period a bright green 

 appears ; then the green is subjected to the action of a solution of 

 bichromate of potash, and the tint is changed to a deep blue, which, 

 has been called azurine. 



Engraving and Printing. In this department the novelties which 

 seemed most worthy of specification were, first, illustrations of a pro- 

 cess (not new, see Annual of Scientific Discovery, 1861, pp. 68, 69) 

 for enlarging or reducing impressions from engravings, through the 

 elastic power of India-rubber. Thus a picture is first printed on a 

 sheet of vulcanized rubber prepared with a surface to take litho- 

 graphic ink ; this is then stretched to any required size, and the 

 enlarged impression transferred to a lithographic stone, from which 

 other impressions on paper may be taken in the usual manner. 

 When it is required to make a reduced copy of a drawing, the pro- 

 cess is reversed. There is now on exhibition in London a series of 

 enlarged sketches in oil from Punch by John Leech, which have been 

 formed in this way from the original wood-cuts stretched and painted 

 over. Second, lithographs transferred to copper and chemically ti cated 

 to become surface-blocks by Giessendorf of Vienna ; third, engraved 

 photographs on wood, with which the draughtsman has had nothing 

 to do ; fourth, one of Hogarth's engravings, reduced and engraved by 

 the action of light, producing a repetition that would puzzle a con- 

 noisseur to make out, the work of Sir Henry James; and, lastly, 

 specimens exhibited by Mr. Willis of what he calls autotypography 

 a process by which he is enabled to impress in a plate of soft metal an 

 artist's own drawing, even to his washes and delicate renderings, pro- 

 vided they be done upon the transparent medium supplied by him, 

 somewhat as drawing upon tracing paper, an easy and facile method, 

 requiring no reversing of the subject or writing. 



Engraving by Electricity. An ingenious, though not very, new 

 machine, was exhibited for engraving copper cylinders employed in 

 the printing of textile fabrics by means of electricity, its distinctive 

 feature being the application of voltaic electricity in communicating 

 certain necessary movements to important and delicate portions of 

 the apparatus. The cylinder to be engraved is first coated on its 

 outer surface with a thin film of varnish, sufficiently resistant to the 

 continuous action of the strongest acids. The requisite number of 

 copies of the original design are then traced or scratched simultane- 

 ously by a series of diamond points, which are arranged on the ma- 

 chine parallel with the axis of the cylinder. Each diamond point is 

 in correspondence with a small temporary magnet ; and the entire 

 series is so arranged en rapport with the original design, which had 

 been previously etched on a metal cylinder fitted in with a non-con- 

 ducting substance (this cylinder being made to revolve in contact 

 with a tracing-point), that when the electric current passes, intermit- 

 tent currents are established, whereby the diamonds are withdrawn 

 from their work at the proper intervals. The metallic surface is 

 thereby exposed in certain parts, and a bath of nitric or other acid 

 being afterwards used to etch or deepen the engraved portion, the 



