142 BACTERIA IN RELATION TO PLANT DISEASES. 



Previous to development the exposed plate should be placed in the tray, flooded 

 with water, and gently rubbed with the balls of the fingers, particularly if the 

 exposures have been made for some time, or in dusty weather, or on plates which 

 have been opened for some time. Many "pin holes" will be avoided by this practice, 

 and frequently one will be astonished at the amount of dust which can be felt as 

 the fingers are passed over the plate. 



Negatives should be fixed in strong hypo for ten minutes (a little longer 

 exposure will not harm them), hardened in alum-water (saturated) five or ten 

 minutes if the weather is hot, and washed in running water one to two hours. If 

 these rules are followed, negatives which are good on the start will not spoil after- 

 ward. Weak hypo should not be used, neither should the solution be saturated, but 

 only nearly so, i. e., a saturated solution diluted with one-sixth water. This is made 

 up in small quantities in advance. The saturation is accomplished, not by throwing 

 the crystals into a jar containing water, but by putting them into a cloth-sack which 

 is brought into contact only with the top layers of the water. On removal from 

 the washing-box the back and face of the negative should be rubbed over carefully 

 under running tap water with a wad of soft cotton, and set away in a clean place 

 to dry after rinsing in distilled water. If one is in a great hurry to get a print from 

 a wet negative, it may be dried in about ten minutes by soaking for eight minutes 

 in 95 per cent alcohol and then holding it near an electric fan. 



In developing in deserts or in southern climates, in very hot weather, all the 

 fluids must be iced, including the wash-water, or else the plate must be hardened in 

 2 per cent formalin water for five minutes before the development begins. Alum- 

 water can not be used for this purpose, since it greatly retards development. 



It often happens, especially with beginners, that a good negative (one rightly 

 exposed) is spoiled by being left in the developing solution too long or by being 

 taken out too soon. An overdeveloped negative may be reduced after soaking it 

 in water (or preferably before it has dried) by placing it for a few minutes in a tray 

 of clean water, to which has been added a small quantity of hyposulphite of soda 

 and a few drops of a 10 per cent solution of red prussiate of potash (Farmer's reduc- 

 ing solution), which, of course, must be uniformly distributed. Thin negatives, free 

 from hypo, may be intensified, if they are thin simply from underdevelopment, by 

 exposure for from two to five minutes (occasionally a little longer) in a strengthening 

 solution made of Agfa intensifier 20 parts and water 180 parts, or by soaking them 

 in a strong watery solution of mercuric chloride until they are whitened through 

 uniformly on the back, and then blacking them by soaking in ammonia water 

 strong enough to give off disagreeable fumes. If the time of exposure is not nearly 

 correct, another negative should be made. Negatives thin from overexposure do 

 not intensify well ; neither do those which were much underexposed. All negatives 

 should have the subject, date of making, and degree of magnification written on 

 them with a lead pencil as soon as they are dry. The proper place for a record is 

 on the margin of the negative itself rather than in a book or on a bag. which may 

 become misplaced, although it is convenient to have it also on the envelope, or 

 negative-bag. 



