Bainbow Phosphorescence. 137 



RAINBOW PHOSPHORESCENCE. 



Under this title we propose to describe a series of curious 

 preparations made in France with great perfection, and capable, 

 after exposure to sunshine, electric light, or magnesium light, 

 of emitting in a dark chamber, very beautiful luminous effects, 

 red, blue, yellow, and green. The substances sold for this 

 purpose are enclosed in long flat bottles, and placed side by 

 side in a box, the lid of which is removed when the experi- 

 ments are made. The origin of all such preparations may be 

 found in the ' ' Bologna phosphorus," well known to all chemical 

 students. It appears that in 1602 Vincenzo Cascirolo, an arti- 

 san of Bologna, engaged in alchemical pursuits, accidentally 

 made a phosphorescent sulphide of barium by calcining sul- 

 phate of baryta in contact with charcoal, and this material, 

 which attracted the greatest interest amongst philosophers, 

 was subsequently named the u Bologna stone/ 7 or " Bologna 

 phosphorus." In 1675 Baudouin described a similar pre- 

 paration made by calcining nitrate of lime, and named it " her- 

 metic phosphorus." To prepare Bologna phosphorus, sulphate 

 of baryta is reduced to powder, moistened with water or white 

 of egg, and made into cakes, which are placed in layers of 

 braise (charcoal ashes), and calcined in a furnace. 



In his recent work on light, M. Becquerel* states that 

 Margraf, who published an account of his experiments in 1862, 

 by pulverizing and calcining these substances two or three times 

 in succession (as recommended by Pothier), obtained a mixture 

 of phosphorescent tints, and thus to some extent anticipated the 

 more recent preparations we shall proceed to describe. At 

 the end of the sixteenth century, Homberg introduced his 

 phosphorus made from chloride of calcium; and in 1780, 

 Dufay published a memoir, showing that many minerals, 

 shells, and calcareous concretions exhibited similar properties 

 after calcination ; and Beccaria soon afterwards demonstrated 

 that insolation, or exposure to sun-light, imparted the property 

 of phosphorescence to a considerable number of dried organic 

 substances, and other materials. In the course of his experi- 

 ments Beccaria devised a phosphoroscope, or rotating appara- 

 tus, for exposing a substance to the light, and then exhibiting 

 it to an observer situated in the dark. By these means, which 

 have been improved in later times, a very slight degree of 

 phosphorescence may be rendered visible. Zanotti, secretary 

 of the Bologna Academy, about the same time observed that 



* " La Luniere ses Causes et ses Effets," par M. Edmund Becquerel, 

 de l'Academie des Sciences, de l'Institut de France, Professeur au Conservatoire 

 des Arts et Metiers, etc. Paris : Firmin Didot. 1867. 



