Mabch 11, 1904.] 



SCIENCE. 



435 



to denote ' a series of rocks ' or an ' interval 

 in the time-scale.' In any case, tlie name 

 Bradfordian is well known to students of 

 European Mesozoic rocks, having been pro-, 

 posed by Desor in 1859, for Upper Bathonian 

 rocks, as exemplified at Bradford-on-Avon in 

 England. Dr. Girty doubtless overlooked this, 

 although he might have found it in Professor 

 Eenevier's valuable ' Chronographe geologique' 

 published by the International Congress of 

 Geologists. 



It is always a pity when the names of well- 

 known European places are applied by geolo- 

 gists to newly established stratigraphical 

 divisions in other countries. Instances of 

 this, both in the British colonies and in the 

 United States of America, are perplexingly 

 numerous. Even such terms as ' Cussewago ' 

 and ' Cuyahoga ' are to be preferred. 



E. A. B. 



SPECIAL ARTICLES. 



NOTES ON FLUORESCENCE AND PHOSPHORESCENCE. 



The phosphorescent and fluorescent proper- 

 ties of natural minerals have attracted con- 

 siderable notice and some highly interesting 

 papers have been recently written on the sub- 

 ject, but artificial products of this class do 

 not appear to have claimed much attention. 



It is well known that minerals found in 

 one locality may fluoresce brightly under 

 suitable excitation, while other specimens, ap- 

 parently similar, but taken from another lo- 

 cality, may be unresponsive under a like 

 excitation. 



It is also well known that a minute trace 

 of certain substances, when properly incor- 

 porated with a large quantity of another sub- 

 stance, will sometimes impart fluorescent and 

 phosphorescent properties to the latter. For 

 example, if a trace of manganese chloride 

 is fused with sodium chloride, the latter will 

 fluoresce red under ultra-violet light, whereas 

 sodium chloride fused by itself will show no 

 color fluorescence. It, therefore, appears al- 

 together probable that the fluorescent proper- 

 ties of some natural minerals is due to the 

 presence of another substance in minute quan- 

 tity, and in the absence of this constituent 



an otherwise similar mineral may be non- 

 fluorescent. 



The writer having given some study to the 

 artificial production of fluorescent and phos- 

 phorescent compoimds, is tempted to present 

 a description of a few simple experiments in 

 the hope that their results may prove interest- 

 ing to other investigators, and thus lead to 

 further developments in this fascinating fleld 

 of research. 



The ultra-violet light used for testing was 

 made by a small high-tension arc produced by 

 a condenser discharge between two iron balls 

 about one half inch in diameter, the air gap 

 being adjustable and the condenser being 

 charged by an alternating current of 60 cycles 

 and 120 volts, stepped up to about 5,000 volts. 



Experiment No. 1. — Zinc .sulphate was dis- 

 solved in a small quantity of distilled water 

 holding a trace of manganese sulphate in so- 

 lution. The mixture was boiled to dryness 

 and then calcined at a full red heat in a 

 porcelain crucible for about thirty minutes. 

 The resulting white powder fluoresced a light 

 pink and phosphoresced an intense red, having 

 the appearance of being red hot. 



Experiment No. 2. — Zinc chloride was dis- 

 solved in a small quantity of distilled water 

 holding a trace of manganese sulphate in solu- 

 tion. An equal quantity by measure of soda 

 silicate of a syrupy consistency was then 

 added and the mixture triturated to a thick 

 cream. It was then dried and calcined at a 

 full red heat in a porcelain crucible for about 

 three hours. The resulting white powder 

 showed a light green fluorescence and phos- 

 phoresced brightly the same color. 



Experiment No. 3. — Substituting cadmium 

 chloride for zinc chloride, but otherwise using 

 the same ingredients and treatment as de- 

 scribed in the last experiment, the resulting 

 white powder fluoresced a light pink and phos- 

 phoresced an orange yellow. 



Experiment No. Jf. — Cadmium sulphate was 

 dissolved in distilled water with a trace of 

 manganese sulphate, evaporated to dryness 

 and calcined at a red heat in a porcelain 

 crucible for fifteen minutes. The resulting 

 powder fluoresced a dull yellow, and phospho- 

 resced a light green. The phosphorescence of 



