RANVIKR'S PICRO-CARMINE. 103 



fluid. Ranvier was, in fact, led to add picric acid to ammoniacal solution of 

 carmine by the desire of neutralising the ammonia, that is all. 



The good qualities (especially that of precision and delicacy of stain) 

 above attributed to picro-carmine apply in their entirety only to Ranvier's 

 picro-carmine or " picro-carminate of ammonia." The other pseudo-picro- 

 carmines are in general so inferior as not to take rank as good stains at all. 

 The reader is in consequence warned against an over-confident faith in them, 

 and is especially warned against the so-called picro-carmine sold by the 

 opticians. The true Ranvier's " picro-carminate of ammonia " can only be 

 prepared with certainty by one process as yet known. This I proceed to 

 give, and amongst the other formulae set out one or two that may by chance 

 give rise to the formation of a picro-carminate, and should at all events 

 afford a useful staining solution (which the majority of these formulae only 

 do by chance). 



For slow staining, dilute solutions may advantageously have 1 or 2 per 

 cent, of chloral hydrate added to them. 



Overstains may be washed out with hydrochloric acid, say 0'5 per cent., 

 in water, alcohol, or glycerin. 



Preparations should be mounted in balsam, or if in glycerin this should 

 be acidulated with 1 per cent, of acetic or, better, formic acid. 



160. RANVIEE'S Picro-carmine or Picro-carminate of Ammonia. 



The method of preparation employed in the Laboratory of Histology of 

 the College de France, kindly communicated to myself and Henneguy for 

 our Traite des Meth. techn. (q. v., p. 451) by M. VIGNAL, one of the 

 assistants there, is as follows : 



Take- 

 Water . 1000 parts. 



Picric acid 20 



Carmine . . . . . . . 10 



Ammonia ....... 50 



Put them into a stoppered bottle and leave them for two or three months 

 in a warm place. Then put them into a large crystallising dish and let 

 them putrefy. When the liquid has become reduced by evaporation to four 

 fifths of its original volume, remove the crystals that have formed at the 

 bottom, dry them, and dissolve them in a little warm water. Filter the 

 solution, and examine it with the microscope to see whether the carmine is 

 really dissolved. If not, add water and ammonia, and let the solution 

 putrefy again ; evaporate and examine as before. When you have got your 

 carmine combined, evaporate the solution to dryness in a stove, and reduce 

 the picro-carminate to powder. 



For staining, dissolve 1 grm. of the powder in 100 grms. of water, 

 and add a crystal of thymol to prevent the development of mould. 



RANVIEE'S Original Formula (Traite, p. 100) was as follows : To a 

 saturated solution of picric acid add carmine (dissolved in ammonia) to satu- 

 ration. Evaporate down to one fifth the original volume in a drying oven ; 

 and separate by filtration the precipitate, poor in carmine, that forms in the 

 liquid when cool. Evaporate the mother-liquor to dryness, and you will 

 obtain the picro-carminate in the form of a crystalline powder of the colour 



