262 HOW TO WORK 



340. The Fixing Solutions may be made as follows : 

 Hyposulphite of soda 4 o/., dissolved in 4 oz. of water. Using 



it repeatedly until saturated with the dissolved out iodide and bro- 

 mide of silver ; but Dr. Maddox prefers a fixing solution made by 

 dissolving about 



8 grains of cyanide of potassium in one ounce of water. 

 It should be marked POISON. As this substance varies in its strength, 

 the solution should be made so as to clear the plate in a gradual 

 manner in from one to one and a-half minutes, but not so strong as 

 to destroy the half tones. The same solution can be used repeatedly, 

 or until rendered, by using, too weak. It should not be kept exposed 

 to the air. 



PRACTICAL MANIPULATION. 



This is naturally divisible into three distinct stages : i, obtaining 

 the image on the sensitised plate ; 2, rendering it visible ; and 3, 

 obtaining a print upon paper. 



341. Cleaning the Glass Plates. The glass plates, whether of 

 " patent plate," which is the best, or of " polished flatted crown," 

 are first to have the sharp edges removed by a grooved roughening 

 stone sold for the purpose ; this is best done under a gentle stream 

 of water from a tap, that the particles of grit or dust may be carried 

 away : the plate is then dropped into a clean pan containing a hot 

 solution of washing soda in rain or soft water. After lying in this for 

 a little time, they are singly washed over back and front with a 

 pledget of tow and saturated solution of washing soda, then dropped 

 into clean hot soft water. When all the plates have been treated in 

 this way, they are taken out to drain, the water thrown away and fresh 

 hot water poured into the vessel. The plates are singly dipped under 

 the surface of the clean water, then wiped with chemically clean linen 

 cloths, such as old napkins, one covering the left hand in which the 

 plate rests, the other being used to dry and polish the plate. These 

 cloths are not to be washed with soap and water, but to be well washed 

 out in hot soft water, containing a little soda, then well rinsed in fresh 

 water and dried. 



It is advisable to keep a stock of plates thus partially prepared. 

 To further clean them, examine the plate along the edge, and if any 

 very slight curvature exist, let this be taken as the surface on which the 

 collodion is to be poured. Select three chemically clean dry cloths, 

 fold one into double thickness, and on it hold the plate in the left 

 hand, face down ; with one of the other cloths polish well the back, 

 breathing on it from time to time ; then turn it face uppermost, have 

 a little old collodion which may be slightly weakened with alcohol, 

 place a pledget of clean cotton wool in a small cleft stick or whale- 



