438 New Gutlines of Chemical Philosophy. 



there ir. probably a (liniinution of oKVgeii, from the oxidation of 

 the iron ; and it is not certain that the ashes afforded by the 

 charcoal from vegetable substances exist in it in the state of 

 earths and alkalies: and as the quantity of hydrogen varies ac- 

 cording to the degree of heat to which charcoal has been ex- 

 posed, it is almost useless to attempt to assign its proportion in 

 any jiarticular case, especially when the largest portion is so ex- 

 tremely minute. 



The nature of the chemical difference between the diamond 

 and other carbonaceous substances may be demonstrated by an- 

 other process, namely, igniting them in chlorine ; when common 

 well burnt charcoal, or plumbago from Cumberland, is intensely 

 ignited in chlorine, white fumes are immediately perceived in 

 consequence of the production of muriatic acid gas by the hy- 

 drogen, v.hich acid precipitates the aqueous vapour in the chlo- 

 rine ; but the diamond occasions no such effect. A small dia- 

 mond, weighing •4.") of a grain, was kept in a state of intcuje 

 ignition by the great lens of the Florentine Museum for mere 

 than lialf an hour ; but the gas suffered no change, and the dia- 

 mond had undergone no diminution of weight, and was not 

 altered in appearance. 



Charcoal, after being intensely ignited in chlorine, is not al- 

 tered in its conducting power or colour ; and this circumstance 

 is in favour of the opinion, tlir.t the minute quantity of hydro- 

 gen is not the cause of the great difference between the physical 

 properties of the diamond and charcoal. 



LXVIII. New Outlines of Chemical Philosophy. 

 By Ez. Walker, Esq. of Lynv, Norfolk. 



[Continued from p. 365.] 



W HAT has been advanced upon evaporation in my last paper, 

 receives considerable support from a series of experiments car- 

 ried on by Mr. Six, to investigate the variations of Iwcal heat. 



On December 19, 1783, this gentleman disposed of three 

 thermometers, of a peculiar construction, in the following man- 

 ner ; one in his garden ; one on the top of St. Thomas's hill, at 

 fifteen feet from the ground, which was nearly on a level with 

 a third placed on the top of the high tower of Canterbury ca- 

 thedral, at about 220 feet from the ground. From observations 

 taken with these instruments he found, that 



*' The local variations in the day time seemed to be regulated 

 by the general degree of heat only, without being affected by 

 any other particular disposition of the atmosphere, or the clear- 

 ness 



