and plate. In the front is introduced a piece of glass, protected 

 by a slide, to enable the operator to watch the developement of the 

 picture. A small thermometer is usually added, the bulb of which 

 dips into the iron trough, to enable the operator to observe the 

 temperature of the mercury. 



IODINE AND BROMINE TROUGHS, (FiG. 7.) 



These are either of glass or Berlin ware, encased in wood ; 



they are furnished with 

 frames of various sizes 

 to hold the plates, and 

 with a cover of slate or 

 glass. They may be 

 used for any of the sen- 

 sitive solutions. 

 Fig. 7. 



POLISHING BLOCK WITH COVER, (Fie. 8.) 



This block is made of a 

 shape and size convenient 

 to the hand : the plate ad- 

 heres firmly to the prepared 

 surface of the block, but 

 may be readily disengaged 

 when the process of polish- 

 ing is completed. 



Fig. 8. 



THE BUFF, (FiG. 9,) 



Consists of a piece of wood of suitable dimensions, generally 



about twelve inches by 

 "^X three, covered with se- 

 ^x, veral folds of white 

 cotton velvet, thorough- 

 ly cleansed from dirt, or 

 grease. 



Fig 9. 



