Natural Dyes 215 



bodies with boiling water, treating the extract with lead acetate or 

 barium hydrate, and then decomposing the lead or barium carmin- 

 ate with sulfuric acid. The exact composition of carminic acid is 

 still somewhat uncertain; so far as known, it is: 



CH3 OH 



CO I CeHiiOs 



HO / CO I OH 

 COOH OH 



It is a fairly strong dibasic acid and forms readily soluble salts with 

 the alkali metals, and insoluble salts with the heavy metals. 

 Aluminium carminate (obtained by precipitation from aluminium 

 acetate and carminic acid or ammonium carminate) is soluble in 

 aqueous or weak alcoholic solutions of acids. 



A slightly different aluminium compound, formed by mixing 

 alum and carminic acid is used in histology. This combination 

 was called carmalum by Mayer (1892, 1899), and has also been 

 used by Grenacher (1879) and Rawitz (1899); it is a useful nuclear 

 stain for sections; and is often employed with light green or indigo 

 carmine as a contrast stain. A so-called muci-carmine, an acid 

 solution containing aluminium chloride, has been employed by 

 Rawitz to stain mucin; while Mayer's para-carmine, containing 

 aluminium and calcium chlorides, is used both for sections and for 

 staining in bulk. By others a combination of iron with carminic 

 acid has been used for similar purposes. 



Carmein. Carmine, kept in ammoniacal solution, changes in its 

 properties, due to oxidation. The oxidized carmine, often known 

 as carmein, can be obtained by treating a carmine solution with 

 hydrogen peroxide and precipitating with alcohol. It is a dark 

 colored mass which can be ground into a black powder. 



PROCEDURES RECOMMENDED BY THE COMMISSION IN WHICH 

 COCHINEAL DERIVATIVES ARE USED.* 



*Under this heading are given references to procedures described in detail in 

 Staining Procedures, edited by Conn and Darrow (1943-4). 



