150 BACTERIA IN RELATION TO PLANT DISEASES. 



of good habits are to use the dark-room, it is very convenient to have developing 

 dishes and fixing trays 011 the same shelf, which may be of slats over a deep sink, 

 as in figs. 132 and 133. With some shelves over this sink and a water-tap above it, 

 everything is in reach without moving about. If, on the contrary', various persons 

 are to work in the dark-room, some of them students with unformed habits, some 

 of them older workers with incorrigibly slovenly habits, including a disposition to 

 spill hypo over everything, then some different arrangement must be made, the 

 sodium hyposulphite trays especially being kept on a separate shelf at a good distance 

 from the developing shelf. Figs. 134 and 135 show the arrangement of a small dark- 

 room devised by the writer for photographic work, the space at his disposal being 

 very limited. The air-shaft is in the ceiling over the loading shelf. Artificial light 

 is furnished by two i6-candle power Edison electric-light bulbs, one hanging near 

 the wall above the sink, the other inclosed in the red-light box. Over the ruby 

 glass there is placed a sheet of orange-buff paper, commonly called post-office paper. 

 The hypo trays are under the sink. The zinc box for washing negatives stands in 

 the sink. Developers are mixed on the drop-shelf, and are kept on the shelves 

 above it. The bromide bottle, graduates, and beakers are kept on the small shelves 

 above the developing shelf. Large bottles of alum solution, hypo solution, etc., are 

 stored under the hypo shelf. 



Enameled plates for squeegeeing silver prints may be stored when not in use as 

 shown in fig. 136. In this way they are protected from dust and scratches. To 

 prevent prints from sticking the surface of the plates is occasionally rubbed with 

 paraffin dissolved in xylol, and is then polished with a soft clean cloth. 



Some memoranda on photographic developers will be found under Formulce. 

 In addition to what has been said there a few hints on salted silver-paper, blue- 

 print paper, and bromide-papers may be of service to those who wish to use these 

 methods as preliminary to pen-and-ink drawing. 



All papers designed for this use should possess a smooth surface suitable for 

 pen-and-ink work, and sensitive papers of this quality may be had of various dealers 

 by specifying just what is desired. Blue-print paper and salted silver-paper may be 

 made for one's self. It is preferable, however, to purchase the former, and to make 

 the latter or to buy it fresh, as it does not keep well. Directions for making the 

 plain silver-paper may be found in " The Figures, Facts, and Formulae of Photog- 

 raphy and Guide to their Practical Use," by H. S. Ward, N. Y., Tennant & Ward, 

 1903; and in "The Photo Miniature," Vol. II, No. 22, "Albumen and Plain Paper 

 Printing." 



All sensitive papers placed in the printing frame should have the coated side 

 next to the film-side of the negative. 



Blue-print paper is much less sensitive to light than solio paper, and long solar 

 printings are required. When the paper has assumed a deep-bronzy appearance it 

 may be assumed to be sufficiently printed. A few trials will give the necessary 

 experience. Blue-prints are developed by simply washing them in several changes 

 of pure water, taking care that the coated surface is wetted thoroughly from the 

 start, /. r., freed from air-bubbles. No fixing is required. 



