186 ANNUAL OF SCIENTIFIC DISCOVERY. 



ent shade. From inquiries they have caused to be made, they have 

 ascertained that if their notes be printed on a yellow tinged paper, 

 in blue ink, it would be impossible to transfer fac-similes to photo- 

 graphic negative wax paper, (rendered sensitive by being saturated 

 with a solution of the nitrate of silver and other chemicals,) from 

 which the imitations of the genuine notes are obtained. 



Another plan, to which the attention of the Bank authorities may 

 be called, and which would be equally efficacious in putting an end to 

 the nefarious system referred to, would be to have a few words, or 

 ornamental devices, struck off on the back of the genuine notes. 

 These words or devices, by the process of sun-printing, would all be 

 transferred to the front of the imitation note, and thus the attempts 

 of the fraudulent to plunder the unwary would be entirely foiled. 

 London Times. 



CHROMATIC PHOTO-PRINTING. 



At a meeting of the London Society of Arts, Feb. 1853, a paper 

 was read by Mr. R. Smith, on " Chromatic Photo-printing, being a 

 mode of printing textile fabrics by the chemical action of light." 

 The author proposes to employ the chemical agency of light in dye- 

 ing or staining textile fabrics ; the cloth, whether wool, silk, flax, or 

 cotton, being first steeped in a suitable solution, then dried in the 

 dark, and subsequently exposed to the action of light, those parts 

 which are to form the pattern being protected by pieces of darkened 

 paper, or some other suitable material, attached to a plate of glass. 

 When the desired effect is produced, the time for which varies from 

 two to twenty minutes, according to the nature of the process, the 

 fabric has to be removed, in order to undergo a fixing operation, 

 whilst a fresh portion of it is exposed to light. This may easily be ef- 

 fected by the use of very simple mechanical arrangements, so that a 

 number of photographic printing engines may be placed side by side, 

 and superintended by one person. From the trials which Mr. Smith 

 has made he believes that even the diffused light of a cloudy day 

 will have power enough for the operation, though of course a longer 

 time will be required for its perfection than on a bright and sunny 

 day. In order to obtain a pale blue or white pattern upon a blue 

 ground, Mr. Smith uses solutions of citrate of tartrate of iron, and 

 ferrocyanide of potassium ; steeping the cloth subsequently in a di- 

 lute solution of sulpheric acid. Browns and buff's are obtained by 

 using a solution of bichromate of potash ; the excess of salt in the 

 parts not acted on bv li^ht being: afterwards either washed out, leav- 



** ^ 



ing those portions white, or decomposed by a salt of lead which forms 

 a yellow chromate of lead. By combining these two processes Avith 

 the use of madder, log-wood, and other dye stuffs, a great variety of 

 tints may be obtained. 



