Method of estimating changes in gases. 33 



of Mr. Gay LuflaC, (how that all the different elaftic fluids, 

 taken at equal temperatures, expand equally by heat, yet we 

 are ftill ignorant of the precife expanfion for increments of 

 (ingle degrees, or of the mode in which the power of expan- 

 fion is affected* by difference of preflure ; or by its relations to 

 aqueous vapour or uncombined moifture. 



The calculations on this fubjecl are confequently laborious Calculation may 

 and complicated ; but it is very eafy to avoid them, by re- be av0ld ^ d b X 

 curring to comparative obfervations, which may be obtained fervations, 

 in a very fimple manner, by means of the manometer. 



By making a given quantity of air, in contact with water w ' c h a ftandanf 

 at a known temperature and preflure, a ftandard, it is eafy, JJJJJj J ° C ° m " 

 in afcertaining the changes produced in it by alteration in the 

 temperature and preflure, to determine, by the rule of pro- 

 portion, the changes that have been produced from the fame 

 caufes in any other quantity of gas, fubmitted to chemical 

 operation ; or to afcertain what would be its volume at the 

 mean height of the barometer and thermometer. 



owing to his not perceiving that he actually deftroyed a portion of 

 the elaftic fluid be was operating upon (aqueous vapour) in re- 

 ducing its temperature fo low ; if his air had been previoufly dried 

 by fulphuric acid, &c. he would not have found fo remarkable di- 

 minution below 72 Q . My experiments give for 77*1 above 55°, 

 167 parts j for the next 77°| only 158 parts: and the expanfion in 

 every part of the fcale feems to be a gradually dimini/hing one in 

 afcending. 



" The refults of feveral experiments made upon hydrogenous 

 gas, oxygenous gas, carbonic acid gas, and nitrous gas, which 

 were all the kinds I tried, agreed with thofe on common air, not 

 only in the total expanfi»n, but in the gradual diminution of it in 

 afcending : the fmall differences obferved never exceeded 6 or 8 

 parts on the whole 325 : and differences to this amount will take 

 place in common air, when not freed from aqueous vapour, which 

 was the fituation of all my factitious gafes. 



" Upon the whole therefore I fee no fufficient reafon why we 

 may not conclude, that all elaftic fluids under the fame prejfure exl 

 pand equally by heat—' and that for any given expanfion of mercury, 

 the correfponding expanfion of air is proportionally fomething lefs, the 

 higher the temperature." 



Mr. Gay Luffac makes the dilatation to be from 100 to 137.5 

 between 32° and 212 Q , which gives for each degree between thefe 

 points ^4-i Seep. 134 j and Annales de Chimie, No. 128, p. 137. 



Vol. IV.— January, 1803. D In 



