152 PRACTICAL PHOTOMICROGRAPHY. 



denser than appears necessary, for the fixing makes a great 

 difference. When the plate is watched by reflected light there 

 should be no sign of degradation of the white where there is 

 no image; as soon as any such " graying " appears the plate 

 must be swilled with water containing enough acetic acid to 

 make it smell distinctly of that acid, the developer being, of 

 course, poured off, either down the sink or into a cup for 

 future use. The developer may be used repeatedly until it 

 either turns muddy or acts too feebly ; each time it is used it- 

 acts with less vigor than previous times, on account of fresh 

 bromide being formed and on account of oxidation. 



Unfortunately it is sometimes impossible to avoid a slight 

 degradation of the white of the slide, this being due to the 

 want of density of the negative ground in comparison with 

 the density of the subject-image. If there is good contrast 

 of density between subject and ground there ought to be no 

 sign of deposit on the slide-ground, and any such deposit is 

 probably due to overexposure of the slide plate or unsafe 

 light. A very slight deposit may be removed by the acid alum 

 and iron solution, used after fixation. After the plate has been 

 well washed in the acidulated water, three changes at least, it 

 may be washed under the tap and fixed in the usual hypo-bath. 

 Thereafter it is to be well washed and then the following 

 poured on and off from a height, in order to clear any deposit 

 that may be on the plate, due to lime salts. 



Saturated Solution of Ferrous Sulphate 4 ounces. 



Saturated Solution of Alum 16 " 



Hydrochloric Acid 1 to 2 drams. 



THE IlYDROQuraoNE DEVELOPER. (MR. EDWARDS.) 

 Mix in the following order: 



Sodic Sulphite, 2 ounces. 



Water 20 " 



Hydroquinone 30 grains. 



Sodic Carbonate 3 ounces. 



Potassic Carbonate 3 " 



Potassic Bromide. 40 grains. 



This solution will not keep good for very long, but if the 

 water be divided into two parts and the carbonates separated 



