. Phosphorescence; or, The emission of light by minerals, plants, and animals. s phenomenon the denomination of Fhosphores-cence after insolation has been given. The substances which possess this property inthe highest degree are the Bologna stone_, or solarphosphorus, certain varieties of fluor-spar andcarbonate of lime, some fossils, calcined shells orpearls, phosphate of lime, arseniate of lime, diamonds shine with brilliancy in the darkif they have previously undergone an exposure ofsome seconds^ duration only to solar light. But 12 phosphorescence: no substance surpasses in this
. Phosphorescence; or, The emission of light by minerals, plants, and animals. s phenomenon the denomination of Fhosphores-cence after insolation has been given. The substances which possess this property inthe highest degree are the Bologna stone_, or solarphosphorus, certain varieties of fluor-spar andcarbonate of lime, some fossils, calcined shells orpearls, phosphate of lime, arseniate of lime, diamonds shine with brilliancy in the darkif they have previously undergone an exposure ofsome seconds^ duration only to solar light. But 12 phosphorescence: no substance surpasses in this respect sulpliuretof barium. It is now a long time since tlie cobbler of Bologna^in Italy_, astonisbed and amused bis friends with apeculiar substance since known as Bologna fhos-phoTiis, Bologna stone, or Solar phosphorvs, wbicbsbines brightly in the dark after having been placedin the sunlight for some time. This substance issulphuret of barium. The cobbler prepared it byheating red-hot with charcoal a piece of sidiiliateof harijta, or Barytine, (Fig. 1,) a stone which he. Fig. 1. picked up in the secondary strata of the MontePaternOj where he found it in lumps of considerableweight.* The German chemist, Marggraf, used toprepare solar phosphorus by powdering down thestone, and making it into thin cakes, with a mix-ture of flour and water, before submitting it tocalcination. This Bologna phosphorus^^ was thefirst substance known to become phosphorescentafter insolation, and, consequently, it has been * Barytine is found abundantly in Derbyshii-e, Cumberland,the Isle of Arran, etc. AFTER INSOLATION. 13 submitted to many and varied experiments. It isbest obtained by tlie calcination of pulverizedsulpbate of baryta, made into a firm paste witbcommon gum. It should be preserved in a bottlewMcli closes hermetically witli a glass stopper. Wben sucli a bottle and its contents are ex-posed to the rays of the sun, or even to daylight,for a certain time, and then taken into a darkroom,
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