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, and has also been used by Grenacher 

 and Rawitz; it is a useful nuclear stain for sections, and is often 

 employed with light green or indigo carmin as a contrast stain. A 

 so-called muci-carmin, an acid solution containing aluminium 

 chloride, has beem employed by Rawitz to stain mucin; while 

 Mayer's para-carmine, containing aluminium and calcium chlo- 

 rides, 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. Carmin, kept in ammoniacal solution, changes in its 

 properties, due to oxidation. The oxidized carmin, often known as 

 carmein, can be obtained by treating a carmin solution with hy- 

 drogen peroxide and precipitating with alcohol. It is a dark colored 

 mass which can be ground into a black powder. 



Orcein and Litmus c. i. no. 1242 



Both orcein and litmus are obtained from certain lichens, Lecan- 

 ora tinctoria and Rocella tinctoria. These lichens are colorless, but 

 when treated with ammonia and exposed to the air, blue or violet 

 colors develop. The colors are due to certain acids, one of which is 

 orcin : 



OH 



/ 



\ 

 OH 



Orcin, acted upon by air and ammonia, becomes orcein. 



ORCEIN 



The exact formula of orcein is unknown. It is a weak acid, 

 soluble in alkalies, with a violet color. 



In alcoholic solution Unna has used orcein for staining elastin 

 tissue; he has employed it for connective tissue, following poly- 

 chrome methylene blue; and for plasma fibrils in the epithelium, 

 following anilin blue; also with anilin blue or acid fuchsin in study- 

 ing the process known by him as chromolysis. It has found less 

 frequent use among other histologists; but has been employed by 



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