308 Progress of Invention. 



PROGRESS OF INVENTION. 



Photo-printing. — Attempts Have been made in various ways to 

 multiply copies of photographs by means of the press ; but hitherto 

 the mode in which the various shades are produced by photography 

 have been an insuperable obstacle to complete success. The diffi- 

 culty, it is probable, has now been overcome, and simultaneously by 

 two persons, by very simple means — the combined use of the 

 principle of carbon printing, and of an ink which, unlike that 

 ordinarily employed, produces a depth of shade dependent on 

 quantity. A glass plate, after having been coated with a mixture 

 of gelatine and sugar, and sensitized with bi-chromate of ammonia, 

 is exposed in the usual way under a negative ; after which the 

 gelatine, which has not been rendered insoluble by the action of 

 light, is washed away. A positive picture in relief is thus produced ; 

 and a copy of this, in a substance suited to the purpose, is 

 obtained for use in printing. This copy may be made by means 

 of the electrotype process, or by placing a sheet of soft metal over 

 the picture in gelatine, laying both between slabs of cast iron, and 

 subjecting to pressure ; or simply by pouring melted sulphur on the 

 gelatine. The electrotype copy is troublesome on account of the 

 mounting required ; but as the indentations are deeper it gives 

 better impressions than the plate of soft metal. The copy in sul- 

 phur will answer very well in some cases. 



To take impressions, ink is made by soaking gelatine in water, 

 then melting it and mixing with it carbon, or even a colouring matter, 

 in very fine powder. If colouring matters are used, they must not 

 be such as are acted upon by the bi-chromate. To take an impres- 

 sion a small quantity of the ink, kept in the fluid state by heat, is 

 poured on the centre of the electrotype, or other copy ; a sheet of 

 photographic paper is placed on this, and over the paper a plate of 

 glass ; after which, a pressure is applied, that forces the ink into all 

 the hollows, leaving little or none elsewhere. When the ink is cold, 

 it adheres only to the paper, along with which it is entirely removed 

 from, the electrotype, especially if, after several impressions have 

 been taken, the plate is slightly greased. All the effects of light 

 and shade are produced by the varying thickness of the ink which 

 has been thus transferred to the paper. 



New Mode of Filtering Water. — Capillary attraction has been 

 adapted by M. Aman Vigie, to the filtration of water ; and as the 

 principle seems easily applicable on the large scale, the method he 

 uses will, most probably, be very generally adopted. While, looking 

 to the sources whence we are obliged to obtain water for domestic 

 purposes, the necessity of filtrating it is universally admitted, the 

 mode of effecting this thoroughly and rapidly is attended with con- 

 siderable difficulty, on account of the stopping up of the pores of the 

 filter. M. Vigie having observed that when a fluid is raised by 

 means of capillary attraction, the particles of solid matter floating 

 in it do not rise along with it, it occurred to him that this fact, in 

 conjunction with the principle of the syphon, might be applied, even 



