90 HYDROMETALLURGY. [ HI. 



brought to correspond by means of a tightening screw, so that 

 the albumen, when either spreading or shrinking, may always 

 cover the whole surface of the intermediate plate of glass. 

 The frame is furnished on two parallel sides with a small 

 groove to receive the albumen — which a small round-edged 

 knife, elevated to the proper point by means of two spiral 

 pivots cased in the sides of the box, and kept down in a pa- 

 rallel direction to the glass by means of a screw, serves to 

 remove, thus producing the exact thickness of layer which is 

 required. The frame is furnished along one of its sides with 

 an indented ridge, to which a wheel provided with an external 

 handle corresponds, so that the frame can be made to move 

 with such velocity, as the operation may require. 



