140 W. HATCHETT JACKSON, 



monobasic acids forms three salts, in which one, two, or 

 three atoms of hydrogen are replaced by the acid radicle. 

 The triacid salts are obtained in the presence of an excess of 

 acid, and are all colourless, or nearly so, for the most part 

 having a dull reddish-brown tint.* All salts of rosaniline 

 are soluble in alcohol, ether, glycerine, and chloroform, and 

 in fluids containing more than a certain percentage of these 

 substances. Some, e.g. the mon-acetate or mono-chloride, 

 are soluble also in water or watery solutions. Hence a 

 stained tissue plunged into water loses a certain amount of 

 colour, and is ultimately left in a most unsatisfactory condi- 

 tion. Moreover, under the influence of light and in the 

 presence of organic matter some of the mon-acid salts undergo 

 a decomposition by which a nearly colourless compound is 

 formed and the preparation thereby spoilt. 



It appeared to me that two things were necessary : 



(1) To find a stable mon-acid magenta salt. 



(2) To obtain a proper preservative fluid. 



The second condition can only be fulfilled by employing a 

 ■watery solution, as a// magenta salts will dissolve in glycerine, 

 glycerine and water, Canada balsam, dammar varnish, &c. ; 

 the first, by employing a mon-acid salt, insoluble or other- 

 wise, unchangeable in such a preservative fluid. 



The salt I have found preferable is the mono-tannate ; my 

 preservative fluid is syrup prepared in a new way. 



(1) At first I stained the given tissue in magenta (solution 

 of crystallized magenta, or Judson's magenta dye), and then 

 washed the stained tissue in a weak solution of tannic acid. 

 This plan is troublesome in practice, and the results are 

 uncertain, so that at last it was given up and the tissue 

 stained from the first with the mono-tannate. The best way 

 of making the staining solution is this : — Prepare a strong 

 solution of tannic acid in water, dissolve a little crystallized 

 magenta in water (or pour some of Judson's dye into a test- 

 tube and add some water) ; both solutions must be cold. 

 Add the tannic acid solution to the magenta drop by drop, 

 shaking the test-tube from side to side after adding each 

 drop, and taking care not to precipitate the magenta solution 

 completely. Let the precipitate settle; pour ofi" the fluid, and 

 wash the precipitate by decantation several times with cold 

 water. Finally, let it partially dry, and add first a drop of 

 acetic acid, then alcohol guttatim till it dissolves. The solu- 

 tion is pink, and stains very quickly and deeply. 



(2) Of the preservative solution I have used two kinds, and 



' But the mon-acid salts, on the coutrary, are brilliantly coloured. 



