PRINTING METHODS LANTERN SLIDES IO9 



and perfectly white. It may be procured of 

 any photo-stock dealer. The chemicals are 

 but two in number, both very cheap, and 

 should be chemically pure. They are potas- 

 sium ferricyanide (red prussiate of potash) and 

 ammonia citrate of iron. To make the sen- 

 sitizing solution, dissolve just before using, 64 

 grains of the red prussiate in i ounce of 

 water, and 100 grains of the iron citrate in a 

 like quantity, keeping them separate to the 

 last moment, when they are to be filtered 

 together through a wad of wet cotton wool 

 placed in the bottom of a small funnel. The 

 paper, having been previously pinned by its 

 four corners to a smooth board or table-top, 

 is now to be gone over with a fine sponge 

 dipped into the filtered solution, in regular, 

 broad strokes, first from left to right, always 

 in one direction, until its surface is com- 

 pletely coated; then at right angles to the 

 first coating, ending at the upper right hand 

 end. If properly done the surface will be 

 smooth and even, without lines or marks of 

 any kind. A little practice will make perfect, 

 as in other things. The sheet must then be 

 hung up in a warm place to dry, which it will 

 do very quickly. All of these operations 

 must be done by lamp- or very subdued day- 



