244 Pigments and Minerals (chap. 17) 



H0SO4. Keep at or below 25 °C. About 4.7% performic acid is formed 

 within 2 hours, but it deteriorates after a few more hours. 



PERACETic acid: to 95.6 ml. glacial acetic acid add 259 ml. of 30% 

 HoOo (undiluted reagent) and 2.2 ml. concentrated HoSO^. Let stand 

 1-3 days. Add 40 mg. disodium phosphate as stabilizer. Store at 

 0.5°C. Keeps for months in refrigerator. 



Chlorate Method of Removal 



Treat sections 24 hours in 50% alcohol plus small mount of potas- 

 sium chlorate and a few drops of HCl (concentrated). Wash 10 

 minutes before staining. 



Bromine Method of Removal 



1% bromine in water: 12-24 hours. Wash well before staining. 



Chromic Acid Method of Removal 



Mixture of equal parts of 1% chromic acid and 5% calcium chlo- 

 ride, aqueous: 8-12 hours. Wash well. 



Peroxide Method of Removal 



10% H2O2: 24-48 hours. Wash well before staining. 



The peroxide method is considered by some to be the best; it is 

 specific for melanin; other pigments resist longer than 48 hours. The 

 permanganate and chromic acid methods bleach all pigments, which 

 allows for no differentiation among them. 



Formalin pigment 



Brown and black crystalline granules and artifacts, produced by 

 formalin, are fovmd in and around blood. 



Baker {1938) Method of Removal 



1% potassium hydroxide in 80% alcohol, or picric acid dissolved 

 in alcohol, until precipitate is removed. 



Murdoch {19-45) Method of Removal 



3% H2O2, 25 ml.; acetone, 25 ml.; and 1 drop ammonia, until 

 precipitate is gone: 1-2 hours. 



Barrett {1944) Method of Removal 



Saturated solution of picric acid in alcohol: 10 minutes to 2 hours. 



Malarial pigment 



This appears as amorphous brown-black granules. 



