18 INTRODUCTION. 



Upon cooling, a slight sediment is deposited. After filtration 

 from this sediment the liquid is evaporated to dr}-ness, and 

 afterwards dissolved in water in the proportion of 1 : 100. 



Another formula is: 1 gram of carmin and 4 c. c. of concen- 

 trated ammonia are mixed with 200 c. c. of water, and 5 grams 

 of picric acid then added. After nearlj' complete solution the 

 clear liquid is poured off, and exposed to the air for some weeks. 

 The red powder left after this slow evaporation is to be dis- 

 solved when required in water in the proportion of 2 :100, and 

 the solution filtered through two thicknesses of filter-paper. 



Cochineal, the substance from which carmin is prepared, may 

 be used in aqueous extract, or with alum. The formula for the 

 preparation with ahnn is given as follows : Rub to a fine powder 

 one gram of cochineal with one gram of burnt alum ; mix with 

 100 c.c. of water, and boil down to 60 c. c. Wlien cold, filter the 

 solution several times, and add a few drops of carbolic acid. 



90. Ilmmatoxylin (a dj-e obtained from logwood) is used dis- 

 solved in alcohol, or alum-water, according to circumstances. 



Fre}- gives the formula: 1 gram of haimatoxylin is dissolved 

 in absolute alcohol. This solution is added, drop b}' drop, to a 

 three per cent aqueous solution of alum, until it becomes deep 

 violet in color. After exposure to the air for a few days, it is 

 to be filtered, and is then ready for use ; but a fresh filtration 

 will be found necessarj- after a time. Poulsen advises that a 

 few drops of a ten per cent solution of alum be added to an 

 aqueous solution of hsematoxylin (.3.5 gram in 10 c.c. water). 



Aqueous extracts of several other d3-e-woods can replace 

 htematoxylin in some cases, but they have no advantage over it. 



91. Picric acid (trinitropheuic acid) in aqueous solution is 

 valuable for staining and hardening protoplasm. It may be 

 used alone, combined with carmin (see 89), or with nigrosin. 



92. Alkanet-root (alkanna) in alcoholic solution tinges resin- 

 ous globules and serves to prepare for cutting specimens which 

 contain them. The method of use is described under " Resins." 



93. The coal-tar colors. Under this name are comprised the 

 anilin derivatives and a few others of a slightlj- different origin. 

 The following table will indicate to some extent the changes of 

 color which may be expected when these dyes are used with 

 tissues Avhich have a marked acid or alkaline reaction. But it 

 should be observed that the names of several of the dj-es are 

 loosely applied, and that the dyes made by different manufac- 

 turers are not always of the same character or strength. All of 

 the dyes mentioned below are soluble in water and alcohol. 



