Organic Substances 59 



aqueous solutions oflFers on obvious advantages. If loss of 

 water-soluble matter is feared, the slide should be protected 

 with collodion. 



2. Chromic acid.— A 4-5 per cent solution of chromium 

 trioxide in distilled water is used. 



3. N HC/.-Dilute 10 ml. of concentrated HCl (assay, 36- 

 39 per cent ) with 100 ml. of distilled water. 



4. Schiff's reagent.— There are a number of formulas^^"^^ 

 published which all give essentially identical results. SHght 

 variations in the results are due to differences between vari- 

 ous batches of dye and to the age of the solution rather than 

 to minor departures from any of the formulas. The following 

 procedure by Coleman,^^ recommended by Lillie, was found 

 to be simple and reliable: 



Dissolve 1 g. of basic fuchsin (C.I. No. 677) in 200 ml. of 

 boiling distilled water. Cool to about 50° C. Add 1 ml. of 

 concentrated hydrochloric acid (assay, 36-39 per cent) and 

 2 g. of either sodium bisulfite (NaHSOs) or potassium meta- 

 bisulfite (K2S2O5); shake the flask, stopper it tightly, and 

 allow it to stand at room temperature for 24 hours. The dye 

 will be decolorized to a straw yellow or light-brownish so- 

 lution with or without some precipitate floating in it, depend- 

 ing on the quality of the dye used. Add about 0.5 g. of ad- 

 sorbent charcoal (e.g., Norit), shake, and filter the mixture. 

 The filtrate must be crystal clear and colorless; should it 

 have a hght pinkish tinge, add hydrochloric acid drop by 

 drop until all trace of color is discharged. Keep reagent in 

 the icebox. 



Some batches of reagent will remain perfectly usable for 

 over a year; others, for reasons completely unknown, may de- 

 teriorate in a matter of weeks. The source of the dye does not 

 seem to make much difference; reagents of highly variable 

 keeping properties may be prepared from the same commer- 



26. Wermel, E.: Ztschr. f. Zellforsch. u. mikr. Anat., 5:400, 1927. 



27. De Tomasi, J. A.: Stain Technol., 11:137, 1936. 



28. Coleman, L. C: Stain Technol., 13:123, 1938. 



29. Rafalko, J. S.: Stain Technol, 21:91, 1946; Lillie, R. D.: Stain 

 Technol, 26:163, 1951. 



