22 ON ILLUxAIIXATIOK". 



doubtless fo this, the carbonates have crumblecl almost entirely 

 to dust, while the compounds which they had formed with 

 silox remain entire, 

 armiiarexpoii- On the 13th of March, I made a similar experiment, in 

 Sancetocu"' ^^'^^^^^' besides some pounded oyster-shell, I introduced a mix- 

 poUiae Biaibie, tare of chalk, with 10 per cent, of silex intermixed, and 

 ground together in a mortar with water, in a state of cream, 

 and then well dried. The contents of the tube when opened, 

 were discharged with such violence, that the tube was broken 

 to pieces ; but I found a lump of chalk, then in a state of 

 while marble, welded to the compound ; which last, in its 

 fracture, shewed that irregular black colour, interspersed 

 roughly through a crystalline mass, that belongs to the alpine 

 Biarbles, particularly to the kind called at Rome CipoUine, 

 It was very hard and firm ; I think unusually so. It efferves- 

 ced constantly to the last atom, in diluted nitric acid, but 

 luuch more sluggishly than the marble made of pure chalk. 

 A cloudiness appeared pervading all the liquid. When the 

 effervescence was over, a series of bubbles continued during 

 the whole day in the acid, without any disposition to burst, or 

 rise to the surface. After standing all next day and night, 

 they maintained their station ; and the solution being stirred, 

 ■was found to be entirely agglutinated into a transparent jelly, 

 breaking with sharp angles. This experiment affords a direct 

 and positive proof of a chemical union having taken place be- 

 tween the carbonate and silex. 



(To be continued.) 



III. 



Observations on the Dispersion of the Light of Lamps by 

 Means of Shades of vnpolished Glass, Silk, SfC. ; with a 

 Description of a nexo Lamp. jBj/ Benjamin Count of 

 RuMToiiD. Read at the National Listitute of France^ 

 March 20, 180(). 



To Air. NICHOLSON. 

 SIR, 



JL SEND you for your Journal, the following translation of 

 a very ingenious paper of Count Rumford's, which was read 



