150. BRASILLIN, SANTALIN, ETC. 137 



hrematoxylin produces a beautiful violet colour ; it reduces alkaline 

 copper-solution as well as salts of silver and mercury, and cannot 

 be sublimed. 



The best method of extracting hsematoxylin from vegetable 

 substances (such as logwood) is to macerate first with water con- 

 taining a little sulphurous acid and then exhaust with ether 

 saturated with water. (For the spectrum, see Plate I, 7 and 8.) 



Bmsillin resembles haematoxylin, and, like it, is soluble in ether, 

 alcohol and water. Alkalies produce a carmine-red colouration, 

 which disappears when the liquid is warmed with zinc dust, but 

 returns on exposure to the air. The spectrum is shown on Plate 

 I., 9. On boiling with peroxide of lead and water a strong 

 fluorescence is developed. 



Santalin is soluble in ether (yellow), and alcohol (red), but not 

 in pure water. With dilute potash it yields a violet coloured 

 solution, from which chloride of barium precipitates a violet 

 barium-compound. It differs from alizarin in its melting-point 

 (104), in not subliming, and in yielding no anthracene. (For 

 spectrum see Plate I., 10.) 



151. Detection and Estimation of Gallic Acid, Catechin, etc. In 

 addition to the foregoing substances gallic acid, catechin and 

 pyrocatechin are extracted by water from the evaporation-residue 

 of the ethereal extract ( 38). They are deposited in acicular 

 crystals on evaporating an aqueous solution over sulphuric acid at 

 the ordinary temperature, or may be removed by shaking with 

 ether, or preferably, acetic ether. If in sufficient quantity, gallic 

 acid or catechin may be purified by re-crystallization from boiling 

 water, the former being soluble in 3 parts of boiling and about 

 100 of cold water, the latter in 4 and 16,000 respectively. Heated 

 between watch-glasses, gallic acid yields a white sublimate of pyro- 

 gallol, together with black non-volatile melangallic acid. Catechin 

 yields pyrocatechin. (Of. 38 and 42.) Cone, sulphuric 

 acid dissolves gallic acid colourless in the cold, but on warming 

 the liquid becomes wine-red and crimson. The addition of water 

 now causes the separation of rufigallic acid, which is coloured 

 transient blue by cone, potash. If only traces of the latter acid 

 are present they may be extracted, according to Barfoed, 1 from the 

 aqueous liquid by agitation with acetic ether containing spirit, 

 and the residue obtained on evaporation treated with potash. 

 1 Barfoed, Lehrb. d. org. qual. Analyse. Lief. 1, 63. 



