112 THE BOOK OF THE LANTERN. 



mediate coating of the plates can be bought ready made, 

 with full instructions for coating and development. 



This method yields results which cannot easily be beaten, 

 It was introduced about twenty years ago by Messrs. 

 Bolton & Sayce, and a number of good workers have 

 since taken it up successfully. As its name implies, a 

 collodion is employed containing bromide of silver, and 

 although many might be deterred from attempting it, from 

 the fancied difficulties which it presents ; yet, in practice 

 it is by no means a complicated process to work. It has 

 certainly a great many advantages. When the sensitised 

 collodion is once compounded it will keep for a long time. 

 Plates can be coated with it a dozen at a time if required 

 and after being dried by artificial heat are ready for 

 immediate use. When the printing from the negative has 

 been performed, these plates, after development and a 

 minute's washing, can be dried, and the slides are finished 

 and ready for the lantern. 



A plain collodion is first of all made with high tempera- 

 ture Pyroxyline, and the usual solvents, ether and alcohol. 

 To this is added ammonium-bromide and citric acid. The 

 silver is now dissolved in as little water as possible, and is 

 added to the bromised collodion. The emulsion is then set 

 aside to ripen for some hours, is poured out into a dish for 

 the solvents to evaporate, and is then broken up into small 

 pieces and washed in several changes of water, so as to get 

 rid of the soluble salts which are not required. All these 

 operations are, of course, conducted in non-actinic light. 

 When these pieces have been finally drained as closely as 

 possible, they are once more dissolved in the requisite pro- 



