224 PRACTICAL MICROSCOPY. 



In cases where, from over-exposure, it has been impos- 

 sible to obtain density with the alkaline developer, a most 

 careful washing should be given after fixing, with a view to 

 remove the last trace of ammonia. 



Intensification can then be effected with acid pyro. and 

 nitrate of silver, or with protosulphate of iron and' nitrate of 

 silver. The author has a decided preference for the latter, 

 and uses the following formula, viz. : 



A. 



Protosulphate of iron 15 grains 



Gelatine- acetic acid solution (as described 



below) 40 drops 



Water I oz. 



B. 



Nitrate of silver 10 grains 



Acetic acid, glacial, 50 10 drops 



Water I oz. 



The gelatino-acetic acid solution is compounded as 

 under: 



Gelatine .. .. _ r . .. .. 15 grains 



Acetic acid, glacial, 50 . . 3 drachms 



Water .. .. .. 5 drachms 



and it is well to prepare a stock of this, and also of A, as 

 they are both better for keeping. 



To proceed first flood the plate with water and then 

 with a solution of iodine and iodide of potassium of the 

 colour otpale sherry for one minute, rinse it off, and apply 

 enough of A to cover the plate, for about the same 

 time. Now drop into the cup a drachm of B, and 

 bring the A back from the plate to the cup to mix them 

 together. Re-apply, and keep moving over the surface 

 until density is sufficient. If any air-bells should occur 

 they must be kept moving, and then they will do no 

 harm. 



