PHOTOGBAPHIC PEOCESSES 285 



has to be developed, and the slight additional cost of the tabloids 

 as compared with chemicals bought in bulk. 



In some cases of under-exposure, when it is impossible to 

 secure another negative and forced development is therefore 

 absolutely necessary, a small quantity from 10 to 20 drops per 

 ounce of developer of a 10 % aqueous solution of metol may 

 be added to a pyrogallic-acid developer. This method is pre- 

 ferred by some workers to that of adding more than the normal 

 quantity of alkali solution, as there is less liability of the plates 

 being fogged when development is greatly prolonged. 



Intensification. Some negatives, through insufficient de- 

 velopment, may not be dense enough to yield a bright print. 

 An example of this is seen in Plate VII, Fig. 2. This specimen 

 was very faintly stained, and in spite of the use of colour- 

 screens sufficient contrast was not obtainable to yield a 

 bright print. The illustration is taken from the untreated 

 negative ; but had intensification been resorted to, a more 

 brilliant result would easily have been secured. This is 

 a case in which such after-treatment is clearly indicated, 

 and it will often be found when dealing with insufficiently 

 stained bacteriological or similar preparations that it is difficult 

 to get a negative with sufficient contrast, unless after- 

 intensification of the negative is resorted to. 



In some cases where a negative is considerably over- 

 exposed, and is thin, slight reduction followed by intensi- 

 fication will very much improve the result. 



There are many methods of intensification available ; the 

 following will, however, generally be found sufficient : 



Uranium Intensification. 



Solution 1. Uranium nitrate . . 23 grammes. 



Water ... to 1000 c.c. 

 Solution 2. Ferricyanide of potassium 23 grammes. 

 Water ... to 1000 c.c. 



The intensifier is prepared by taking equal parts of these 

 two solutions and adding 2 c.c. of acetic acid to each 50 c.c. 

 of the resulting solution. The plate must be thoroughly well 

 washed after fixing, as it is essential that it shall be perfectly free 

 from hyposulphite of soda, and it is then immersed in the above. 



After sufficient intensification has been effected, the plate 

 must be placed in several changes of distilled water until the 



