ON THE PHOSPHORESCENCE OF BODIES. \o5 



Jet and asphaltum, instead of a spark, afford the same ap- Jet. Asphal- 

 pearance of electric light as bitumen does; but they are not 

 luminous by the explosion. 



Amber gives no spark, but is phosphorescent, especially Amber. 

 that kind termed fat amber. 



Plumbago gives good sparks, and is not phosphoric; but Plumbago. 

 when mixed with clay, and manufactured into crucibles, it 

 affords good sparks, which are flame-coloured and purple 

 upon the surface, and becomes luminous when the shock is 

 taken above its surface. 



Metals, their Ones and Oxides. 



As the metals are excellent conductors of electricity, it is 

 well known that they all afford good sparks; but I have not 

 been able to perceive any material difference in the colour of 

 the electric light, from different metals, unless the metal has 

 been formed into exceeding thin leaves, or otherwise minutely 

 divided, and the spark be sufficiently strong to produce oxi- 

 dation. 



Not one of the metals is phosphoric by exposure to the The metals are 

 light of an electric explosion, if its surface be clean and bright. n . ot P hos P h »- 



This is the only class of natural bodies, which I have yet 

 found uniformly to remain dark after exposure to the electric 

 . light. Some of their ores and oxides, such as the red and yel- 

 low arsenic, haematites, pyrites which is found in chalk, oxide 

 of zinc, and oxide of antimony are very slightly luminous; 

 whilst others, for instance cinnabar, black sulphuret of mer- 

 cury or ethiops mineral of the shops, mundic, galena, 

 blend, and the sulphurets of antimony, minium, litharge, 

 and some other oxides, as readily absorb, and as obstinately 

 retain within their substance, the electric light to which they 

 are exposed, as even the metals themselves. In short I have 

 not met with a single brilliant phosphoric appearance in any 

 of the metals, ores, or oxides, which I have had the opportu- 

 nity of subjecting to experiment. These observations en- Tj iese exp^;, 

 tirely coincide witli the results of experiments on solar phos- ments agree 

 phori by Beccari, who tried every means that his inventive Bec^r^oTi'so- 

 genius could suggest, to render the metals phosphoric, but larphosphori. 

 without success. However it is not surprising, that there 

 should be a tolerably exact agreement between the observa- 

 tions 



