300 CHAPTER XXII. 



Take 



(A) Ferrocyanide of potassium* (sol. sat.) . 90 c.c. 

 Glycerin . . . . . . 50 



(B) Liquid perchloride of iron at 30 . 3 

 Glycerin . . . . . . 50 



Mix slowly and combine the mixture with 3 parts of vehicle. 

 It is well to add a few drops of HC1. 



Carmine-gelatin Masses. 



483. RANVIEK'S Carmine-Gelatine Mass (Traite technique, p. 

 116). Take 5 grms. Paris gelatin, soak it in water for half 

 an hour, or until quite swollen and soft ; wash it ; drain it ; 

 put it into a test-tube and melt it, in the water it has absorbed, 

 over a water-bath. When melted add slowly, and with con- 

 tinual agitation, a solution of carmine in ammonia, prepared 

 as follows : 2\ grms. of carmine are rubbed up with a little 

 water, and just enough ammonia, added drop by drop, to 

 dissolve the carmine into a transparent solution. 



When the carmine has been added to the gelatin, you will 

 have about 15 c.c. of ammoniacal solution of carmine in 

 gelatin, if the operations have been properly performed. 

 This solution is to be kept warm on the water-bath, whilst 

 you proceed to neutralise it by adding cautiously, drop by 

 drop, with continual agitation, a solution of 1 part of glacial 

 acetic acid in 2 parts of water. (When the mass is near 

 neutrality, dilute the acetic acid still further.) The instant 

 of saturation is determined by the smell of the solution, 

 which gradually changes from ammoniacal to sour. As 

 soon as the sour smell is perceived the liquid must be exa- 

 mined under the microscope. If it contains a granular 

 precipitate of carmine, too much acid has been added, and 

 it must be thrown away. 



KAN VIE B states that this is the only way to attain to per- 

 fect neutralisation. Trust must not be put in formulae that 

 profess to indicate the proportions of ammonia and acetic 

 acid necessary for neutralisation, on account of the varia- 

 tion in strength of the solutions of ammonia kept in labora- 



* Erratim " Sulphocyanide " in' 1st edition of ROBIN'S Traite. 



