Experiments on Charcoal. 67 



fan, or an occultation of a fixed ftar. Dr. Olbers was the firft 

 who proved, in 1787, that the comets of 1532 and 1661 were 

 totally different ; confequently, that neither of them could be 

 expected in the year 1789. Aftronomy, therefore, is indebted 

 to Dr. Olbers for having cleared up this point of fo much 

 importance. He (bowed how uncertain the return of thefe 

 comets is; and that it is no fault in the exalted fcience of 

 aftronomy, if predictions, which aftronomers ought never to 

 have ventured to make, are not accomplished. 



From Vienna Dr. Olbers proceeded to Prague and Dref- 

 den, and returned thence to Bremen, where he fettled as a 

 phyfician, and where he footi acquired the confidence of his 

 fellow-citizens, both on account of his fuccefsful practice 

 and of the integrity and affability of his character. Since 

 that time aftronomy has been only the amufement of his 

 lei fu re hours, or a fort of recreation, to relieve and unbend 

 the mind after the fatigue of his profeflional duties. 



We (hall add to this fhort (ketch, that Dr. Olbers lately 

 difcoveVed another planet, or, perhaps, comet, for the point 

 feems not yet determined, of which fome account was given 

 in the laft two numbers of the Philofophical Magazine. 



XV. Experiments on Charcoal. By Clement arid 

 Desormes *. 



AT is generally believed that the charcoal obtained by the 

 decompofition of organic matters ftill contains, notwithftand- 

 ing the a&ton of the ftrongeft heat to which it can be fub- 

 jected, fome remains of the volatile principles to which it was 

 united. 



This opinion is founded upon this circumftance, that by 

 the combuftion of charcoal water is fometimes obtained, 

 which feems to prove the prefence of hydrogen ; and that to 

 form carbonic acid with charcoal lefs oxygen is required than 

 with the diamond ; which might induce a belief that fome of 

 it exifted already in the charcoal. 



The memoir publifhed by us in the 115th number of the 

 Annales de Cbimie, and of which the refults are nearly the 

 fame as thofe obtained by Mr. Cruikfliank, announces the 

 gafeous oxide of carbon as free from hydrogen. 



Several chemifts, convinced of the prefence of hydrogen 

 in charcoal, have fuppofed that this gas is a triple combina- 

 tion of carbon, oxygen, and hydrogen, and that its inflam- 

 mability arifes from the laft-mentioned principle. 

 * From the An>w ! ts de Cbtmit, No. 125, 



Ez It 



