GENEEAL PEELIMINAEY PEEPAKATIONS 203 



A supply of porcelain dishes will be required, and these 

 should be deep and of the best quality. The enamel on cheap 

 dishes very soon cracks, and the chemicals that are in use 

 cannot, therefore, be entirely eliminated from the dish as they 

 tend to lodge in these cracks. The dishes should from time to 

 time be thoroughly cleansed with dilute sulphuric acid, or 

 where they have become silver-stained they should be washed 

 with a solution of permanganate of potash. It is above all 

 things essential to keep the dishes thoroughly clean, and at the 

 end of the development of each plate the dish should be washed 

 out, never being left with any solution in it. Nearly all photo- 

 graphic solutions tend to oxidise rapidly, and it is often very 

 difficult to eliminate them entirely from dishes in which they 

 have been allowed to remain for long periods. A supply con- 

 sisting of three quarter-plate dishes, and two or three about 

 8" x 10" for printing operations, will be found sufficient. In 

 addition a fixing-bath is advisable. This consists of a porcelain 

 trough which has a rack in it to enable a good many plates to 

 be placed in it at one time. A fixing solution may be kept 

 in this and used for a number of plates in succession. The 

 plates are put in the trough on edge, and in this position they 

 are fixed much more rapidly and efficiently. The solution 

 should not, however, be used after it has acquired a distinctly 

 yellow tinge. 



Two or three graduated glass measures will be needed; 

 one containing two drachms, for measuring small quantities of 

 solution, and two others of four and eight ounces respectively. 

 These should always be thoroughly washed out directly the 

 solution contained in them has been poured out, as these 

 measures are often used for widely varying solutions, an 

 admixture of which would have disastrous results. 



As already mentioned, some arrangement must be made to 

 cover the dishes while development is taking place. Nothing 

 is much better than a cheap vulcanite or papier-mache dish, 

 of a size larger than the one actually in use ; that is, a 5" x 4" 

 vulcanite dish inverted over one of a quarter-plate size will 

 effectually screen the plate from the light of the ruby lamp, 

 or from any stray light which might enter the dark-room. 



Draining- and drying-racks may be usefully provided, in 

 which the plates after development and fixation may be placed 



