ComhinafhnS of Light. flS^ 



COMBINATIONS OF LIGHT. 



The celebrated Brugnatelli has lately publiHied at Pavia, 

 in the Anyiali di Cbimka, the following obfervations on 

 light : — .Light is either clieniically united with bodies, or 

 merely accumulated and mixed in them in a mechanical 

 manner but invifible, or it is accumulated in bodies in a 

 vifible (late. 



Light chemically united with bodies, feparates itfelf from 

 them in confequence of its affinity for caloric. A red heat, 

 however, is not ncceflary to difengage light when in this ftate. 

 The black calx of manganefe fhines with great vivacity when 

 thrown upon a very hot, but not ignited, plate of iron. The 

 cafe is the fame with the muriat of mercury (corrofive fub- 

 limat), gray calx of mercury, gray calx of antimony, all 

 calcareous falts, &c. Fine fugar and fugar of milk, when 

 very dry and pounded, {hine with great vivacity on a plate 

 of iron which has been merely heated, but they do not ex- 

 hibit the fame phenomenon on iron brought to a red heat. 

 I'eathers, cotton, and wool, fliine when drawn lightly over a 

 piece of hot iron; and the fpots of a playing card, under the 

 mecircumftances, emit a faint light. Camphor and choco 

 thrown upon a piece of iron of this kind form luminous 

 vapours. Several fluids, under the fame circumflances, pro- 

 duce the like effects. Oil of turpentine poured on hot iron 

 gives a very perceptible light; and the cafe is the fame with 

 fat, oils, fweat, wax, tallow, Etc. Atmofpheric air has not 

 the lead influence in regard to the luminous appearance of 

 thefe fubftances ; as they fhine alfo in vacuo, in carbrmic 

 acid gas, in hydrogen gas, &c. Nay, feveral bodies futfer 

 their light to be difengaged when they are immerfed in ful- 

 phurous acid or in boiling oil. Different bodies, under fuch 

 circumftances, give different quantities of light. 



In regard to bodies in which light is merely accumu- 

 lated mechanically, nothing is necefl'ary to render it free but 

 an approximation of their parts. In this manner the light 

 is, as it were, fqueczcd out; as is the cafe with the quickiil- 

 ver in tl^e barometer when it becomes luminous, vitrioHfed 



tartar. 



