LIGNUM FEPHRITICUM — SAFFOED. 281 



Chips of the sapwood tinged tap water only slightly at first, but 

 when left overnight the infusion deepened to a greenish yellow and 

 glowed with a decided fluorescence. With distilled water neither the 

 sapwood nor the heartwood produced fluorescence as seen by ordi- 

 nary sunlight; but this phenomenon was distinctly visible when, at 

 the suggestion of Dr. Arno Viehoever, pharmacognosist of the Bu- 

 reau of Chemistry, these infusions were held in the ultra-violet rays 

 of a fluorescence lamp; and it was also displayed in ordinary day- 

 light, when a small amount of carbonate of sodium or other alkali 

 was added to the infusions of the wood in distilled water. By boiling 

 chips of the wood in tap water for several hours a deep amber- 

 colored extract was obtained not unlike Madeira wine in color. 

 When placed on the table before a window the surface of this ex- 

 tract appeared to be outlined by a deep blue marginal ring, and 

 when held away from the light or when the light fell upon it ob- 

 liquely the fluorescence of the liquid gave it an opalescent appearance 

 not unlike that of certain mineral oils. A drop of the extract in a 

 glass of water caused the whole glass to glow with fluorescence 

 when held in the rays of the sun admitted through a hole in a screen. 



At the residence of Dr. Alexander Graham Bell, in Washington, on 

 the evening of January 6, 1915, where the wood and accompanying 

 herbarium material were shown by the writer, specimens of the in- 

 fusion exhibited by ordinary electric light failed to show fluores- 

 cence; but afterwards, when held in the rays of an arc light, the 

 liquid glowed with an intense blue light which illuminated the faces 

 of those standing near by. 



Experiments were made by Dr. Lyman J. Briggs, biophysicist 

 of the Bureau of Plant Industry, with a view to determine the 

 possible value of lignum nephriticum as an indicator in titrimetric 

 determinations. The result of Dr. Briggs's observation have not 

 been published, but he recognized at once the advantage which this, 

 like other fluorescent substances, must have over those indicators 

 which show color changes only by transmitted light, especially in 

 testing dark liquids, in which the color of the liquid masks the color 

 changes of the indicator. Eysenhardtia wood has a great advantage 

 over fluorescein itself, from the fact that its extract is readilj'' 

 soluble in cold water. With most acids it does not fluoresce, but 

 in the presence of acetic acid its fluorescence is not destroyed. It 

 can not, therefore, be used as an indication of alkalinity in all cases. 

 As compared with phenolphthalein it has a neutral point nearer the 

 acid end of the scale ; that is to say, it will fluoresce in a solution in 

 which phenolphthalein develops no color whatever. 



Plate 4 is a colored drawing by Mr. J. M. Shull, showing a 

 section of the wood of Eyse^ihardtia polystachya, together with an 

 infusion in tap water of the sapwood, in the smaller phials, and an 



