298 PROCEEDINGS OF THE ACADEMY OP [1883. 



coloring. I have previoiisl}-, at several different meetings of the 

 Section, alluded to my experiments with this agent, and have also 

 shown at different times some specimens of tissues stained with 

 it ; but I did not feel willing to place my results definitely before 

 3'ou, until sufficient time had elapsed to fully test the permanence 

 of the preparation and of the stainings produced by its use. I 

 have placed before you this evening, however, under the different 

 microscopes on the table, a series of preparations, single and 

 double stainings, which will, I think, speak for themselves, and 

 also a sample of the staining fliiid. Both fluid and specimens 

 were prepared nearly a year ago. 



In considering the method of prepai'ation of this fluid, it will 

 be well to review briefly the chemistry of logwood. Logwood is 

 the heart-wood of Haematoxylon Campeachiannvi^ a large tree 

 found in Campeachy, Honduras and other parts of tropical 

 America, and is used extensively in the textile arts for dyeing 

 fabrics of a purple, blue or black color. Among its cliemical 

 constituents are resinous matter, a peculiar tannin, free acetic 

 acid, various salts and nitrogenous principles, and a peculiar 

 principle called heraatin, or hiematoxylon, on which the coloring 

 properties of the wood depend. This hematin is, when pure, 

 perfectly colorless, but affords beautiful red, blue and puri)le colors 

 when in union with an alkaline base and the oxygen of the air. 

 It also combines with the alums to form lakes, that peculiar class 

 of coloring substances of which carmine is so remarkable an 

 example. Now, this lake of logwood is the principle which acts 

 as the dye ; and, in order to obtain the color in all its delicacy 

 and purity, all other contaminating impurities must be removed. 

 The various formulae for the preparation of a logwood staining fluid 

 have nearly all directed the use of the commercial extract of 

 logwood, which, aside from the numerous impurities necessarily 

 found in so crude an article, is totally unfit for tlie purpose, for 

 reasons which I will presently point out. 



As alread}^ mentioned, logwood contains, besides its coloring 

 principle, considerable quantities of tannin — so much, in fact, as 

 to give it a position in the U. S. Pharmacopoeia as an astringent. 

 It is well known that vegetable infusions containing tannin are 

 quickly influenced by the action of both light and air, and when 

 these arc assisted by heat, changes take place very rapidl}'. 

 Under these circumstances, the infusions chanoe color, become 



