COLORING AGENTS. 53 



Czokor recommends the following coloring fluid : 

 7 gm. cochineal are pulverized with an equal quan- 

 tity of calcined alum. This is dissolved in 700 

 e:m. distilled water, and the whole is boiled down 

 to about 400 gm. After it is cool a drop of car- 

 bolic acid is added, and the fluid is filtered. It 

 should last at least six months without deteriora- 

 tion. At the end of this time it should be re- 

 filtered after the addition of another drop of car- 

 bolic acid. 1 



PICROCARMINATE OF AMMONIUM (Picrocarmine). 



This staining agent, which is much used by 

 students of animal histology, is employed in botani- 

 cal micro-chemistry, chiefly for differentiating the 

 nucleus. 2 It is prepared by adding a strong solu- 

 tion of ammonium-carminate to a concentrated 

 aqueous solution of picric acid, until this is neu- 

 tralized. After evaporating it to four-fifths its 

 original volume, it is set aside for a time, and then 

 filtered, when the dark orange fluid is ready for 

 use. 3 Another method has been recommended by 

 Gage. Equal parts by weight of picric acid and 



1 Czokor: Die Cochenille Carminlosung. Arch. f. mikr. Anat., 1880, 

 XVIIL, p. 412 et seq. See also Bot. Centralblatt, 1880, p. 1280. 



2 Treub: Actes du congres international a Amsterdam, 1877, Leyden, 



1879, P- J 46. 



8 Frey: Mikroskop, p. 91. Bachmann: Dauerpraparate, p. 27. 

 Treub: Role du noyau dans la division des cell., 1878, p. 23. Pelletan : 

 Le Microscope, 1870, p. 207. Gage: American Monthly Micr. Journ., 



1880, p. 22; Journal of the Royal Micr. Soc., 1880, Vol. III., p. 501. 



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