THE BOOK OF THE LANTERN, 129 



they will form insoluble particles, which will lead to 

 difficulties later on. In the glass tumbler place 



Silver nitrate ... 77 grains. 

 Water ... ... 2 ounces. 



The common tap water employed will, on account of the 

 salts which it contains, turn milky in appearance when the 

 silver is added. This is of no consequence. The crystal* 

 can be crushed under the water by another glass rod, 

 and complete solution will soon be effected. (The tyro 

 must be most careful to keep each stirring rod distinct, or 

 he will spoil the entire work.) When the crystals have 

 all disappeared, pour into the silver solution, drop by drop, 

 some strong liquid ammonia, stirring the solution vigorously 

 all the time. The liquid will turn coffee-coloured, owing 

 to a precipitation of silver oxide, but as more of the 

 ammonia is added this precipitate is redissolved, and the 

 solution becomes as clear as ordinary water. Only just 

 sufficient ammonia should be added to accomplish this 

 result. Now place the glass tumbler in the pan beside 

 the vessel containing the gelatine mixture, and leave it 

 there to warm for about fifteen minutes. All the fore- 

 going operations can be conducted in the full light of day, 

 but now, when the two solutions have to be blended to form 

 a sensitive emulsion of bromide of silver, the light of the 

 red room only must be called into requisition. 



The flame beneath the pan, or water bath, is now no 

 longer required, so let it be removed. Take both the gela- 

 tine and silver vessels from the pan, and place them on the 

 table. Now stir the gelatine briskly, and add a small 



K 



