648 TECHNIQUE 



Berlin Blue Gelatin Mass: 



Saturated aqueous solution of Berlin 



blue (Griibler's) 100 cc. 



Pure French gelatin (in sheets) 5 to 10 grm. 



The gelatin should be quickly washed to remove dust, etc., and 

 then placed for several hours in a very little distilled water until it 

 becomes swollen and soft. The superfluous water is then poured 

 off, and the gelatin melted over a water bath. The warmed solu- 

 tion of Berlin blue may now be added, a little at a time, and con- 

 tinuously stirred. Finally, the mixture is filtered through cotton 

 flannel which has been previously wrung out of hot water. If the 

 mass is not to be used at once, a few crystals of thymol may be 

 added as a preservative, or, after cooling, a little methylic alcohol 

 may be floated upon the surface of the solidified mass. It is better 

 to use it at once. 



Carmin Gelatin Mass: 



Carmin (Griibler's) 3 grm. 



Ammonium hydrate, strong 6 cc. 



Pure French gelatin 7 grm. 



Distilled water 80 cc. 



The gelatin is prepared and melted as above, 50 cc. of the water 

 being used, and the evaporation replaced. The carmin is rubbed 

 up in a mortar with the remaining 30 cc. of the water, and the 

 ammonia is added to render the carmin soluble. The mixture is 

 now permitted to stand for two hours, after which it is neutralized 

 by the gradual addition of 4 to 6 cc. of glacial acetic acid, the mix- 

 ture being constantly stirred, and the latter portions of the acid 

 diluted with four volumes of distilled water, and added drop by 

 drop. The acid soon changes the color of the mixture from a 

 purplish carmin to a bright crimson. Care should be taken not to 

 add too much acid. When properly prepared, the sense of smell 

 should detect both ammonia and acetic acid, and the fluid should 

 have a dark crimson color (the addition of too much acid produces 

 a brighter crimson). Should the mixture be slightly over-acidified 

 a few drops of diluted ammonia will restore the proper condition. 

 The carmin solution is now added to the gelatin mass, a little at a 

 time and with constant stirring, and the whole is filtered through 

 cotton flannel wrung out of hot water. 



The gelatin mass may be kept for a short time by being covered 

 with methylic alcohol, but is better used at once. 



