152 0/ the State of Vapour 



Note.— imo. Hence we fee that air fi'.turated with rnoidure 

 at high heats is much more expanded than dry air of the 

 fame temperature, as De Luc and general Roy have alfo ob- 

 ferved ; but in temperatures below ^6'^' dry air is more di- 

 latable; which probably induced SaulUire to conclude it was 

 fo at higher temperatures. At 54*5 the difference is very 

 perceptible; for 1000 parts ^rj' air at 32*^ are expanded at 

 54*5°, that is, by az'^" above the freezing point to 1044*67 ; 

 whereas 1000 parts of air faturated with moifturc are ex- 

 tended to 1064*72, and in higher heals, the dilTcrences of 

 expanfion are incomparably greater. 



ado. Hence it is plain why moid air, fuch as that of the 

 Weft Indies, is much more fuffocating than dry air of the 

 fame temperature: for 1000 cubic inches of an*, faturated 

 with moifture at 86' of Fahrenheit, contain nearly 76 inches 

 of moifture which is ufelefs to refpiration. 



3tio. Thefe experiments agree with thofe of general Roy in 

 which fteam was introduced at hazard ; for the general found 

 that from 3a' to 52 each degree gave at a mean 2*588, and 

 confequently thefe 20^ would expand 1000 inches to 105 1 "76 ; 

 and by Schmidt's experiments, much more accurately made, 

 we have 1050*33. 



4to. Schmidt alfo obferved a peculiarity in the expanfion 

 of moift air, previoufly noticed by Roy; for Schmidt found 

 that the expanfibllity of air, faturated with moifture, was 

 fmaller than the expanfibility of pure vapour until the 167th 

 degree of Fahrenheit; but in higher degrees they conftanlly 

 approached nearer to each other. And the general obferved 

 that the mean rate of expanfion, which from 152^ to 172'' 

 of Fahr. was 12 for each degree, did, from the 173'' to the 

 192", increafe to 17-88 for each degree, and inceafed ftill 

 more after the igid to the boiling point. The fluggiflmcfs 

 of expanfion of air, faturated with moifture at about 32', was 

 alfo noticed by the general; and he hence concludes the 

 mean rate of expanfion from o to33*' of Fahr. to be 2*27 

 for each degree, which is fmaller than that of drier air. 



Thefe variations of the rates of expanfibility of moift air, 

 faturated at different temperatures, Schmidt very juftly attri- 

 butes to the variation of the degrees of affinity or adherence 

 of air and vapour to each other at diff^ercnt temperatures. At 

 3a° Fahr. it is very ftrong, and alfo below thatdegree; and 

 hence the ftrong folvent power of air colder than the water it 

 afts upon, remarked by Richman : but if both are equally 

 cold, very little moifiure will be taken up by the air, as al- 

 ready mentioned : and hence I have faid that air diftolves 



vapour 



