Natural Dyes 219 



Its solution is colorless, but it becomes red on exposure to the air, 

 as it is then oxidized into the dye brazilein, which probably has the 

 formula : 



HO /\ O CH 



C— OH 



\ 

 _CH2 



HO O 



With alum it is employed as a nuclear stain (known as brazalum) 

 by Mayer (see Lee and Mayer, 1907, p. 218). It is also used by 

 Hickson (1901) for similar purposes following treatment with iron 

 alum as a mordant. Belling (1928) has employed it in place of 

 carmine for staining plant chromosomes in fixed or fresh material, 

 and Shaffer (1933) for distinguishing paper fibers bleached with 

 sulfite from those bleached with sulfate. 



U50 HEMATOXYLIN C. I. NO. 1146 



Hematoxylin, as is well known, is a constituent of logwood, a 

 product of South America. It was first obtained about 1840 by 

 extracting logwood chips with ether, evaporating, digesting with 

 alcohol and standing with water after distilling off the alcohol; 

 hematoxylin was found to separate out in crystals. A little later 

 a similar method was employed, but instead of using logwood 

 chips, the starting point of the process was with commercial log- 

 wood extract, which is the dried aqueous extract of the wood. 

 In one modern method of manufacture the dried commercial ex- 

 tract is extracted with ether in a continuous extraction apparatus, 

 evaporated to dryness, dissolved in water, filtered and crystallized 

 out of the solution. All of these steps, particularly the ether 

 extraction, are slow and difficult to handle on a factory scale, 

 requiring special expensive apparatus. 



The American manufacture of hematoxylin started during the 

 first World War, just as in the case of the synthetic dyes. The 

 problems presented by its manufacture, however, were quite differ- 

 ent from those presented by the synthetics. They were discussed 

 at about that period by McClung (1923) and Conn (1927). Briefly 

 it can be explained here that the first American hematoxylins, 

 marketed during that war, were very crude and proved quite un- 

 satisfactory; but that during the decade following the war, fre- 

 quent improvement in the supply was made by the manufacturers. 

 The first American product was dark in color; and there was so 

 much demand for a light colored hematoxylin that the manu- 



