98 COCHINEAL AND OTHER ORGANIC STAINS. 



following aqueous salt solutions seern to be the most valuable : alurn, 2 per 

 cent. ; chromic acid, 1 per cent. ; bichromate of potassium, 5 per cent. ; ace- 

 tate of copper nearly saturated. After soaking in one of these, the section 

 is passed quickly through distilled water, and placed at once in Weigert's 

 hseinatoxylin (1 part of the crystals in 10 parts alcohol plus 90 parts water), 

 and may be left a short time for direct colouration, then washed and 

 mounted, or a longer time until they become black and are to be washed out 

 by Weigert's iron solution (water 100, borax 2, ferricyanide of potassium 2^). 

 The sections ought to be moved about constantly in the iron solution, 

 otherwise the colour will be extracted irregularly. The copper haematoxylin 

 goes out very rapidly, so that with that stain it is better to dilute the iron 

 solution with twice its bulk of water before placing the sections in it. After 

 the iron solution, the sections must be washed very thoroughly in water, to 

 avoid further fading out, from which one is not entirely secure until the sec- 

 tions are actually mounted in balsam. 



These methods are all merely modifications of Weigert's, Heidenhain's, 

 and Bohmer's methods." 



Glycerin Solutions. 



182. Ehrlich's Acid Haematoxylin (Zeit. f. wiss. Mile., 1886, 

 p. 150). The ordinary (alum) hsematoxylin staining solutions 

 easily decompose, giving rise to a blue precipitate which is 

 formed by the splitting up of the alum into free sulphuric acid 

 and a basic, lake-forming compound of alumina. By adding 

 to a solution an appropriate acid this decomposition may be 

 prevented. The end may be attained by acetic acid. Take 



Water 100 c.c. 



Absolute alcohol . . . . 100 c.c. 



Glycerin 100 c.c. 



Glacial acetic acid . . . . 10 c.c. 



Haematoxylin ..... 2 grammes. 



Alum in excess. 



Let the mixture ripen in the light until it acquires a dark 

 red colour. It will then keep, with a perfectly constant 

 staining power, for years, if kept in a well-stoppered bottle. 

 Sections are stained in a few minutes. The stain is also very 

 appropriate for staining in the mass, as over-staining does 

 not occur. 



In order to get a blue stain with this acid solution, the 

 stained objects should be washed out with common drinking 

 water, which is always slightly alkaline, and not with dis- 

 tilled water. 



For double-staining, either " acid colouring matters " 



