[ 193 1 



XXXIV. On the chemical Knowledge which the Vhilofophers 

 of the :6tb and I'jlh Centuries had of the different GciJ'es'^. 



M, 



.ODERN chemlftrv has been of the utmoft fervlce to 

 the fcience of nature in general, bv making us better ac- 

 quainted with the finer fubltances of light, caloric, and, in 

 particular, of the gafes ; but very imperfect would be our 

 knowlcdiie of nature, very poor would be our harvelt of new 

 truths, aiul verv infisnificant would be our progrefs in our 

 refearchcs rofpetling"'nature, if we had not reafon, froin the 

 rapid advance which philoibphy has made in modern times,' 

 to flatter ourfelves with the hopes of a more accurate know- 

 ledcc of thefe finer iubaances. We fhould, however, be 

 guittv of a very great error, if we afcribed the whole merit 

 of tl'iis more accurate knowledge to the i8th century; for, 

 though moll of the philofophers of the two preceding cen- 

 turies either overlooked thcfe kinds of gas altogether, or con- 

 fidered them as common air corrupted and deprived of its 

 elalVlcity, \et fome of them were more clear- ligh led, and pe- 

 netrated deeper into thefe fecrels of nature. 



If we pafs over the remotefi; traces which occur here and 

 there in the works of the antient writers, J. Baptill van Hel- 

 mont feems to fland at the head of tliofe more acutc-fighted 

 philofophers ; for, though it cannot be denied that he dis- 

 figured his valuable difcoveries by numerous fiilions, and 

 concealed them under new and commonly barbarous names, 

 which were for the mod part improper ; yet he firlt Informed 

 phvlicians and naturalifls, and proved clearly by obleryations 

 and experiments, that, belides the air which we continually 

 breathe, there are other fluids, which, thot.gh they approach 

 very near to the air in lubilely, tranlparency, and particularly 

 in eUilioity, yet differ from it very much; and, as they dilfer 

 alfo from vapours, he has diftinguifhed them by the parii- 

 iular name of gas\. He endeavoured to eltablifli the dif- 

 fj-rencc between them bv this circumltance — tliat asairnou- 

 hflies flame, thcfe fluids exlinguifh itt, and even the vital 

 Jlamc§. He was acquainted aflb with the air of the cele- 



" Kiom Gltihtfifcbes 'Jtjio-n^il der N.iiurwiffaicbnfien, by J. F. Gmelln, 

 ".ul. i. p. 4. 



+ Ortus Medicine 5 Amftcrdam 1643. 410. p. 7j. 



J Ibid. p. 1O3. 



^ Ibid, p. 47.1)7. 95. I to. 1C3. 



VoL^r^ N brated 



No. 43. 



