French Nalional Injlitute. 187 



the other hand, when their length is much lefs than thirty- 

 three times their diameter, there is a very great advantage in 

 tempering them white. The caufts of thcfe varieties will he 

 detailed in the fecond part of this memoir; and it will there 

 be feon, favs the anth(^r, that they only confirm tl'icorv, 

 which he has always compared with experience, in the dif- 

 ferent mcnjoirs publi(hed in the volumes, of the Academy of 

 Sciences and thofc of the Inflitute. 



Phvfks. 



C. Cuvier, fecretary, read the followine notice : 

 On the Gas obtained from the TicduBmn of the Oxide of Zinc, 

 and the Nature of Charcoal. 



The aeriform fluid obtained by reducing the oxide of zinc 

 by charcoal was itated bv C. Guyton to be a gafeous oxide 

 of carbon, that is to fay, carbonic acid with excefs of bafe. 

 Continuing to reafon on this hypothefis, Guyton thouoht 

 that the iub Trance found there in excefs, being very much 

 divided and weakly retained, ought to be very much difpuied 

 to exercife its affinities, and that it could operate reduftiona 

 cold and in the wet way. Trials, however, made with folu- 

 tions of lead, mercury, and filver, did not anfwer his exneila- 

 tion. The gas experienced no alteratiou in ihefe liquors^ 

 but when put in contacl; with oxygenated muriatic acid there 

 WAS a fpontaneous combuftion, and the gas, converted into 

 common carbonic acid by the acceffion of the oxygen of the 

 muriatic acid, became capable of precipitating lime water. 



Bertliollet had a peculiar opinion in regard to the manner 

 in which this redutSiion of the oxide of zinc takes place, and 

 which he explained by the compofition of common charcoal, 

 which contains a large quantity of hydrogen. 



This do6lrine he has endeavoured to ellablifli by a verv 

 extcnfive diflertation on the nature of charcoal, and the dif- 

 ferent products thence obtained. 



For this purpofe he refunicd all the labours of his prede- 

 ccdbrs on charcoal, and fubjeiteJ them to a new examina- 

 tion, ile has lliown that Lavoiiicr was not altoocther exaft 

 in his analyfis of the carbonic acid, bccanfe af that period 

 he was not well acquainted with the fpecilic gravity of oxygen 

 gas, and becaufe he did not pay attention to the water, of 

 which the carbonic acid always contains a great deal. IJo 

 brinies f<jrwaid the proofs wliich C. Monge gave of thislalt- 

 nKiiiioned fact, and has eltablilhed, that common charcoal 

 contains a large quantity of hydrotrcn and a little oxygen, 

 Hr has (howii that this charcoal diddled in a pneumalo- 

 rbeini'.al apparatus gives carbonated hydrogen gas only as 



lou^ 



