NATURAL PHILOSOPHY. 1G5 



say in its original size and round form, for the ordinary dinner-plates, half, 

 or any other proportion of the size, for desserts or cheese-plates, and twice 

 the size and oval for dishes, etc. All this, we have said, is a mechanical 

 process; but it is also a scientific one, and to be properly worked out, we 

 need hardly say, it will require artistic guidance. The textile and the 

 ceramic manufacturer are almost equally interested in this invention with the 

 publisher; but the range of its application seems to be commercially almost 

 unlimited. The process is carried through by means of elastic blocks and 

 electro-metallurgy; all that is required to be furnished the manipulator is an 

 impression of the plate to be copied. The inventor is Mr. H. G. Collins, who 

 has protected his invention by patents, and a company, called the Electro 

 Printing-block Company, has been formed for working it." The details of 

 this process are not as jet given. Editor Annual. 



Cutting 8f Bradford's Photo-lit JiograpMc Process. This process of taking 

 photographic images on stone, which gives promise of great success, is sub- 

 stantially as follows : To reproduce a line-engraving, the lithographic stone 

 may have a polished surface; but to obtain a landscape, where gradations of 

 shade are required, the surface should be grained. This grained surface is 

 coated with a solution of gum-arabic, sugar, and bichromate of potassa, 

 the sugar preventing the immediate fixing of the gum upon the stone, and 

 the chromic salt causing it to become more firmly fixed, or much less soluble, 

 on exposure to light. When the coating is dry, the stone may be exposed 

 in the camera a sufficient time to fix the gum at those parts of the picture 

 where the lights are to appear. The stone is next to be washed with a solu- 

 tion of soap, which attacks the stone, removing the unfixed portions of the 

 coating, and taking the place of these on the surface of the stone. After 

 this, it is to be washed with clean water, and dried. An inking roller is now 

 to be passed over the stone, to ink the soapy portions of the surface, and 

 give an additional body to the picture, the fixed parts of the coating hav- 

 ing been previously damped, to enable them to resist the ink, and when 

 brought up to color, the printing off of impressions may be proceeded with. 



FIZEAU'S PROCESS FOR PHOTOGRAPHIC ENGRAVING. 



A process devised by Mr. Fizeau, of Paris, is as follows: He takes a 

 " Daguerrean " silver plate, and uses on it a mixture of nitrous, nitric, and 

 hydrochloric acids. This mixture does not attack the whites of the picture, 

 but the blacks are acted upon immediately. The resulting chloride of silver, 

 as it impedes the action of the acid, is removed with a solution of ammonia, 

 so that the action may continue. It is complete when a finely-engraved plate 

 has been produced. The lines are then filled up with drying-oil, and the 

 surface electrotyped with gold. The rarnish then having been removed out 

 of the engraved lines, by means of caustic potash, the surface has grains of 

 resin sprinkled over it, for the purpose of producing the engraver's aquatint 

 ground, and the action of the acid is renewed, until the lines shall have 

 acquired sufficient depth. The plate being of silver, is too soft to print from; 

 a copy is therefore taken in copper, by electrotype. Not long ago there was 

 shown, at the meeting of a scientific society, a paper covered with repre- 

 sentations of coins, printed from a plate engraved in this manner. The 

 engraving was so exquisite, that each coin seemed to be presented actually 

 in relief. 



Sclla's Process. M. Sella, of Biella, in Piedmont, has pointed out the 



