of Plate-sulphate of Potash. 408 



The luminosity of salts in the act of ciystallizing, and espe- 

 cially of sulphate of potash, both pure and mixed with various 

 salts of soda, has been made the subject of repeated experimental 

 investigation by several chemists. The extended and interesting 

 researches by Rose* must be generally known. In Gmelin's 

 * Chemistry ' we have a condensed but faithful account of the 

 results observed by different experimenters. The subject is still 

 involved in considerable obscurity. 



I regret that I am as yet unable to give a satisfactory expla- 

 nation of the phajnomena in regard to the salt now under con- 

 sideration, having reluctantly been obliged, by an enforced re- 

 laxation from all such work, to discontinue for a time the expe- 

 riments undertaken to elucidate the subject. I may mention, 

 however, the principal phenomena that have been observed in 

 the trials already made. 



1st. The phosphorescence is not Aasible so long as the tempe- 

 rature of the crystallizing liquor is much above 100^ F. ; but as 

 the temperature falls below this, the scintillations become vivid 

 and frequent. 



3nd. When a rod of glass, of wood, or of metal, is drawn 

 across the surface of the crystalline mass below the liquor, a line 

 of brilliant light is produced in the track of the rod. 



3rd. On breaking the layer of crystals that frequently forms 

 on the surface of the liquor, Aivid sparks are emitted as the de- 

 tached portions sink to the bottom of the vessel. 



4th. On plunging a mass of the crystals into hot liquor and 

 immediately withdrawing it, a few scintillations are visible ; but 

 if the crystals are kept in the hot liquor for a few minutes, and 

 then plunged into nearly cold liquor, the flashes are very bril- 

 liant, and diffused over the entire surface of the mass. 



5th. The most beautiful effect, however, is produced when a 

 quantity of moderately warm liquor is dashed upon a crop of 

 crystals in a vat, from which the mother-liquor has some hours 

 preWously been drawn off. The crystals become instantaneously 

 illuminated with myriads of beautiful and vivid coruscations. A 

 second quantity of the same heated liquor thrown upon the mass 

 gives a much less brilliant effect, and a third quantity scarcely 

 any flashes. But if a bucket of perfectly cold liquor is dashed 

 upon the crystals immediately after the hot liquor has ceased to 

 give scintillations, the result is even more splendid and striking 

 than in the last experiment. 



When the heated liquor is dashed upon crystals of chloride of 

 potassium, or upon wood, or iron, or ice, no visible effect is pro- 

 duced. 



6th. In recrystallizing the salt, no phosphorescence is visible. 

 * Poggendorff's Annalen, vol. lii. 



