CARMINE AND COCHINEAL STAINS. 171 



)3. So-called " Neutral," and Alkaline. 



219. Ammonia-Carmine. In my opinion there is no valid excuse for 

 using ammonia-carmine at all at the present day. 



If. however, such a stain be used, care should be taken to get rid of the 

 free ammonia as completely as possible. This may be done by boiling until 

 the excess of ammonia has evaporated. (So long as free ammonia is present 

 large bubbles are formed in the fluid, and the latter shows a dark purple 

 colour. When the free ammonia has evaporated small bubbles appear, and 

 the solution takes a brighter red tint.) 



One per cent, each of carmine and ammonia in distilled water is a good 

 proportion. 



But a safer mode of preparation is that of RANVIER, as follows (kindly 

 communicated by Dr. MALASSEZ, see Traite des Methodes techniques, etc., 

 of Lee and Henneguy, 1st edit., p. 82). Make a simple solution of 

 carmine in water with a slight excess of ammonia, and expose it to the air 

 in a deep crystallising dish until it is entirely dried up. It should be 

 allowed to putrefy if possible. Dissolve the dry deposit in pure water, and 

 filter. 



220. Magnesia-carmine (MAYER, Zeit.f. wiss. Mik., xiv, 1897, p. 23). 

 Take 1 grm. carmine, O'l grm. magnesia usta, and 50 c.c. distilled water, 

 boil for five minutes, filter, and add three drops of forinol. This is the 

 stock solution. A weak solution may be made by boiling O'l grm. carmine 

 for half an hour in 50 c.c. of magnesia water (made by leaving O'l grm. of 

 magnesia usta in contact with 100 c.c. of spring water for a week with 

 frequent agitation, and decanting when required for use). Mayer says 

 these solutions are less injurious to tissues than the other alkaline 

 carmines. 



221. As to Picro-carmine. The term " picro-carmine" is commonly 

 used to denote a whole tribe of solutions in which carmine, ammonia, and 

 picric acid exist uncombined in haphazard proportions. RANYIER, to whom 

 we owe the invention of picro-carmine, claims that when prepared by his 

 process it results as a definite chemical substance, a double salt of picric and 

 carrainic acid and ammonia, or picrO'Carminate of ammonia. But this is 

 certainly not the case, for carmine is not carrainic acid, see supra, 205. 

 It should be understood that the raison d'etre of picro-carmine does not lie 

 in its capacity of affording a double stain. The double stain, if that is all 

 that is wanted, can be just as well or better obtained by staining first with 

 borax-carmine, or the like, and after-staining with picric acid. The essential 

 point about picro-carmine is that it is less alkaline than ammonia-carmine. 

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

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

 always is alkaline, and is frequently injurious to tissues. 



Compare the paper of MAYER, Ueber Pikrocarmin, in Zeit.f. wiss. Mik., 

 xiv, 1, 1897, p. 18. 



