1883.] 



MICROSCOPICAL JOURNAL. 



87 



2. Ferrous sulphate (green 



vitriol), 2 oz. 



Water, 8 oz. 



Acidify with a drop of sulpliuric acid 

 to each ounce of water. To make the 

 developer, add one ounce of No. 2 to 

 five of No. I. 



The ferrous oxalate developer can 

 be used until it ceases to give vigorous 

 images, and even then it may be re- 

 juvenated by the addition of a few 

 grains of powdered sulphate of iron. 

 The fifty-grain solution of bromide 

 should also be at hand while develop- 

 ing with the ferrous oxalate, to use in 

 case of over-exposure. 



For negatives we prefer to use the 

 pyrogallic developer, as it seems to 

 give a finer deposit on the negative than 

 the oxalate. The latter, however, is very 

 highly esteemed by many persons. 

 The former is the cheapest developer 

 known. 



The pyrogallic developer is capa- 

 ble of great changes in composition to 

 meet different circumstances. Bear 

 in mind that the addition of more 

 soda accelerates the development ; 

 increase in the proportion of pyro- 

 gallic acid gives greater density. 

 Therefore, for an under-exposed plate 

 the solutions may both be made a 

 trifle stronger with benefit. The use 

 of soda tends to loosen the film of 

 gelatin from the plate, so development 

 should not be very slow while using 

 this solution. 



The ferrous oxalate may also be 

 changed to suit special requirements. 

 Thus, for an instantaneous view re- 

 quiring very strong development, take 

 an ounce and a half of the solution 

 of potassic oxalate, and just before 

 using add 30 grains of ferrous sul- 

 phate in powder. The above will do 

 for a 4X 5 plate. 



We w'ill now suppose that an ex- 

 posure has been made, and that the 

 plates are to be developed. Develop- 

 ment must be conducted by ruby 

 light, dry-plates being acted upon by 

 the yellow light used by photogra- 

 phers who work with wet-plates. 



Pass into the dark room, arrange 

 the ruby lantern so as to throw the 

 light over the developing pan, place the 

 exposed plate, sensitized side up, in the 

 latter, then mix the solutions of soda 

 and pyrogallic acid and flow them over 

 the plate. Have the solution of bromide 

 at hand for immediate use in case 

 of need. If it is thought the ex- 

 posure was about right, add two or 

 three drops of the bromide to the 

 mixed developer. If the image comes 

 out too fast, showing an over-exposed 

 plate, add to the developer several 

 drops more of the bromide solution 

 (2-8), to act as a restrainer. A drug- 

 gist's dropping tube with rubber top 

 is excellent for this purpose. 



Watch the development with care. 

 The difficulty the beginner meets with 

 is to know when to stop the process. 

 It must continue until all the details 

 are developed. Nevermind the dark 

 shadows or the high lights, but look 

 at those parts where detail is to be 

 sought for — where the gradations of 

 light and shade are delicate and very 

 fine. Soon the developer begins to act 

 at such places, and if the detail is fine 

 the plate darkens and all the detail is 

 obscured. Apparently the picture is 

 spoiled. — But the process is not yet 

 done. Lift the plate up, and look at 

 it from the under side. The general 

 features of the picture must be seen 

 there, and the details must be indicated 

 by the darkening of the film more or 

 less throughout, before the develop- 

 ment can be regarded as done. The 

 appearance of the developed plate as 

 seen from beneath will depend upon 

 the thickness of the sensitized film. 

 The operator will soon learn how to 

 treat the particular brand of plates he 

 uses. 



Ferrous oxalate development is 

 conducted in precisely the same way. 



If the development has progressed 

 properly, as soon as it is judged to be 

 complete wash the developer off under 

 a tap, or by plunging it into a vessel 

 of water. The pyrogallic developer 

 stains the fingers, and as it can only 

 be used once it is best to pour away 



