14 



HOW TO PHOTOGRAPH 



method adopted by some workers of using 

 the microscope in a dark room, and thus 

 dispensing with a camera. If the student 

 have sufficient room at his disposal, and 

 can fit up an apartment especially for his 



work, perhaps this arrangement is the very 

 best that can be used ; it is, however, hard- 

 ly suited to beginners. The references to 

 each figure will suffice to explain the gener- 

 al arrangement of the apparatus. 



a, Electric light apparatus : an incandescent lamp might be substituted with advantage. The other 

 letters same as in the figure preceding. 



Lesson V. — Development. 



The development of a photo-micrograph 

 does not differ much from that of other 

 negatives, but requires somewhat more pa- 

 tience, as the image on a properly exposed 

 plate is usually slow in appearing, and must 

 not be "forced" in any way. Any ordi- 

 nary dry-plate developer may be used, but 

 the writer has found that known as the sul- 

 phite developer answers best. 



Ferrous oxalate is recommended by some 

 photo-micrographers, notably by Dr. Stern- 

 berg, but is hardly sufficiently "elastic" to 

 satisfy all requirements. It has the great 

 merit of being clean and simple, while it 

 never stains the negatives, as some prepar- 

 ations of pyrogallic acid do ; but the oper- 

 ator will find that with this developer he 

 has very little control over the development. 

 In fact, the development is so mechanical 

 that some operators, like Dr. Sternberg, 

 are content to place the plate in the solu- 



tion and let it take its chance. No one 

 who has become used to pyrogallic acid 

 will ever care to use ferrous oxalate, and 

 the writer would not advise the beginner to 

 use it, but at once to master the difficulties 

 of pyrogallic acid and ammonia. 



However, as some may prefer to try what 

 can be done with ferrous oxalate, the for- 

 mula for this developer is given here : 



Saturated solution of ferrous 



sulphate i part. 



Saturated solution of potassic 



oxalate, 3 parts. 



The potassic oxalate should be neutral, but, 

 as it frequently is alkaline, a few crystals of 

 oxalic acid may be added, until the solution 

 is neutral to test paper. The ferrous sul- 

 phate should be added to the potassic oxa- 

 late, not vice versa. A solution of potas- 

 sic bromide, 20 grains per ounce, should be 

 kept at hand. A few drops of this will be 



