LIGNUM NEPHEITICUM— SAFFOED. 281 



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

 when left overnight the infusion deepened to a greenish j^ellow and 

 glowed Avith 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, pharniacognosist 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 

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

 chips of the Avood in tap Avater for seA^eral hours a deep amber- 

 colored extract was obtained not unlike Madeira Avine in color. 

 "W-lien placed on the table before a windoAV the surface of this ex- 

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

 Avlien held aAvay from the light or Avhen 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 gloAv Avitli fluorescence 

 Avhen 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 afterAvards, Avhen held in the rays of an arc light, the 

 liquid glowed with an intense blue light wdiich 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 obserA^ation liaA^e not 

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

 like other fluorescent substances, must have over those indicators 

 Avhicli shoAV 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 readily 

 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 AvhateA^er. 



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

 section of the Avood of Eysenliardtia 2)olystachya, together Avith an 

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



