6 On Phasplnireicence. 



variation on ineeriing thcni info the various gases ; which 

 provcithnt it is not the result of acon)biisli(jn. That oF vege- 

 table and animal matters becomes brisker, on the contrary, 

 in oxvgen, and disappears in azote, hydrogen, and carbonic 

 acid : nevertheless linseed oil obtained i)y pressure, and 

 heated in a vacuini, or carbonic acid at 125", becomes sen- 

 sibly luminous; but when this light has disappeared it re- 

 mains conslanllv obscure while it is in the same circuni- 

 stancco. When heated in the open air nearly to ebullition, 

 it bums with a shining light, of a quite diflerent naiare, 

 since it is extinguished in the carbonic acid, and is revived 

 in the atmospheric air. The first of these phosphorescences 

 is analogous to that of mineral substances, the second is a 

 true coinbustion. All the melallic oxides made by calcina- 

 tion are inphospliorcseent, at least if they have not passed 

 to the state of semi-vitriJication. 1 hose which we obtain 

 by the humid way lose their phosphorescence by drying 

 them on a filter above burning coals. The phosphate of 

 mercury resists a litile longer ;"but when the filtering paper 

 beffins to turn red, there arises a mass of light, after which 

 it remains dark like the rest. All bodies which have too 

 great a quantity of water in their composition are inphos- 

 phorescent. Slaked lime is very luminous in dry, and very 

 dull in damp weather. The concrete carbonate of lime 

 only gives a few sparks, that of primitive formation is very 

 phosphnrcbcent at an elevated temperature. All substances 

 virhich are melted or softened on the heated supporter, remain 

 obscure. Many mixed substances vihich do not soften at 

 256°, and. which shine very well at this degree uf-hcat, be- 

 come obscure as soon as the temperature is high enough 

 for the particles to be disun.ted. The facility with which 

 the acidulated salts, with the exception of the borates, entei' 

 into fusion, renders them inpho:iphorescent. The acid 

 tartrite of potash shines, however, hut only by the com- 

 bustion of its vegetable principles. The volatile salts mani- 

 fest the same inphosphorescence. Lastly, those which 

 cont-iin a great (juantitv of metallic oxides not dissolved, 

 but mixed with their substance, do not exhibit any phos- 

 phorescence. In general, the substances whicii attract hu- 

 midity very stronglv, <lo not shine except when they are 

 united to a less quantity of water than that which could 

 ■saturate them, or, as is commonly said, slake them com- 

 pletely ; but it is not requisite that they should be totally 

 deprived of it. The author particularly observed the in- 

 lluence of. this circumstance on the phosphorescence pro- 

 duced, by-the alkaline earths in contact with coiicentrated 

 "*"■'' sulphuric 



