1885.] 



MICEOSCOPICAL JOURNAL. 



13 



Photoj^rapliic Methods. 



ny C. M. \ORCE, F. R. M. s. 



I. FOKMl'I.AS lOl? IMUXTING SO- 

 LUTIONS. 



I>///r Prints. The best formula for 

 this process, of many that I have tried, 

 is that furnished by Prof. C. H. Kain, 

 of Camden, N. J., in which the quan- 

 tity of ammonio-citrate of iron is ex- 

 actly double that of the red prussiate 

 of potash, and the solutions strong. 

 This gives strong prints of a bright 

 dark blue, and prints very quickly in 

 clear sunlight. 



Dissolve 6 grains of red prussiate 

 of potash in i dram of distilled water ; 

 in another dram of distilled water 

 dissolve 12 grains of ammonio-citrate 

 of iron. (I use Powers & Wight- 

 man's make.) Mix the two solutions 

 in a cup or saucer, and at once brush 

 over the surface of clean, strong 

 paper. Cover the surface thoroughly, 

 but apply no more than the paper 

 will take up at once ; it should be- 

 come limp and moist, but not wet. 

 The above quantitv of solution, 3 

 drams, will suffice to sensitize ten 

 square feet of paper, or 3 sheets of the 

 • regular' size of plain paper, 18 X 22. 

 As fast as the sheets are washed over 

 with the solution hang them up to 

 dry by one corner. The surplus fluid 

 will collect in a drop at the lower 

 corner, and can be blotted ofl'. 



Black Prints. Wash the paper 

 with a saturated solution of bichro- 

 mate of potash, made quite acid with 

 acetic acid. After printing wash the 

 prints in running water for 20 to 30 

 minutes ; then float them face down 

 on a weak solution (5 to 10 per cent.) 

 of protosulphate of iron for 5 minutes, 

 and wash as befoi^e. If preferred, the 

 iron solution may be washed over the 

 prints, or they may be immersed in 

 it, but floating seems preferable. Af- 

 ter the second washing wash the prints 

 over with a strong solution of pyrogal- 

 lic acid, when the print will develop 

 black, and the ground, if the washings 

 were sufficient, will remain white. A 

 final washing completes the process. 



If a solution of yellow prussiate of 

 potash be used in place of the py re- 

 solution a blue print is obtained. 

 Bichromate prints can be made on 

 albumenized paper by floating it on 

 the solution, and by using a saturated 

 solution of protosulphate of iron and 

 a saturated solution of gallic acid. 

 Ver}- fine prints can be so produced 

 nearly equal to silver prints and at 

 somewhat less cost, but with little or 

 no saving of time or labor. 



Cheap Proof Solution. If old ox- 

 alate developer be exposed in a shal- 

 low vessel in a warm place a deposit 

 of light green crystals will be formed, 

 composed of an impure oxalate of 

 iron. If these crystals be dissolved 

 in water and paper washed with a 

 strong solution, when dry it may be 

 exposed in the printing frame, giving 

 full time. The image is very faint, 

 but on washing in, or floating on, a 

 moderately strong solution of red 

 prussiate of potash for a minute or 

 less a blue positive is produced, which 

 is washed in water as usual to fix it. 

 The unused developer produces the 

 best crystals for the purpose, and the 

 pure ammonio-oxalate of iron is vast- 

 ly better than either. 



All of the above operations, except 

 the printing, should be carried on in 

 the dark room, or by lamp or gas- 

 light only. The solutions and the 

 paper should also be kept in the dark 

 and prepared as short a time as pos- 

 sible before use. 



II. — Compound negatives. 



In photographing with the micro- 

 scope it frequently occurs that the 

 operator, instead of devoting a nega- 

 tive to each of two or more similar 

 objects for comparison, printing both 

 upon the same print, prefers to have 

 the whole series upon one negative, 

 and taking from this a single print. 

 There is often room for two or more 

 images upon the same plate. If the 

 centre of the plate is devoted to one, 

 obviously no more can be accommo- 

 dated on it, but by placing one at 

 each end, or one on each quarter of 

 the plate, both economy of plates and 



