PHOSPHORESCENCE. 333 



pure, and the result is sometimes not very satisfactory ; it is therefore better 

 to make use of some substance whose composition is more to be relied on. 



" When we desire to .prepare a phosphorescent sulphate with lime, or 

 carbonate of lime," says M. E. Becquerel, " the most suitable proportions 

 are those which in a hundred parts of the substance arc composed of eighty 

 to a hundred of flowers of sulphur in the first case, and forty-eight to a 

 hundred in the second, that is, when we employ the quantity of sulphur 

 which will be necessary for burning with carbonate of lime to produce a 

 monosulphate.* It is necessary to have regard to the elevation of the 

 temperature in the preparation. By using lime procured from arragonite, 

 and reducing the temperature below five hundred degrees for a sufficient 

 time for the reaction between the sulphur and lime to take place, the excess 

 of sulphur is eliminated, and we have a feebly luminous mass, of a bluish 

 tint ; if this mass is raised to a temperature of eight hundred or nine hundred 

 degrees, it will exhibit a very bright light." 



Sulphate of calcium possesses different phosphorescent properties accord- 

 ing to the nature of the salt which has served to produce the carbonate of 

 lime employed. If we transform marble into nitrate of lime, by dissolving 

 it in water and nitric acid, and form a precipitate with carbonate of 

 ammonium, and use the carbonate of lime thus obtained in the preparation 

 of sulphate of calcium, we have a product which gives a phosphorescence of 

 a violet-red colour. If the carbonate of lime used is obtained from chloride 

 of calcium precipitated by carbonate of ammonia, the phosphorescence is 

 yellow. If we submit carbonate of lime, prepared with lime water and 

 carbonic acid, to the influence of sulphur, we obtain a sulphur giving a 

 phosphorescent light of very pure violet. Carbonate of lime obtained by 

 forming a precipitate of crystallized chloride of calcium with different 

 alkaline carbonates also gives satisfactory results. 



Luminous sulphates of strontium may be obtained, like those of calcium, 

 by the action of sulphur on strontia or the carbonate of this base, by the 

 reduction of sulphates of strontia with charcoal. Blue and green shades 

 are the most common. Sulphates of barium also present very remarkable 

 phenomena of phosphorescence ; but to obtain very luminous intensity a 

 higher temperature is needed than with the other substances mentioned, and 

 we havethesame result when we reduce native sulphate of baryta with charcoal ; 

 that is to say, when the reaction takes place which produces the phosphorus 

 formerly known as phosphorus of Bologna. Preparations obtained from 

 baryta have a phosphorescence varying from orange-red to green. 



The preparation of such substances as we have just enumerated afford 

 an easy explanation of the method of manufacturing the luminous flowers 

 which we described at the commencement of this chapter. We obtain 

 some artificial flowers, cover them with some liquid gum, sprinkle with 

 phosphorescent sulphur, and let them dry. The pulverulent matter then 

 adheres to them securely, and it is only necessary to expose the flowers 

 * These substances must be finely powdered and thoroughly mixed. 



