48 CORRECTIONS FOR MOISTURE IN GAS. 



Dalton and Gay-Lussac have proved beyond doubt that all gases expand 

 equally by the same increase of caloric when placed under the same circum- 

 stances : it is therefore easy to ascertain the volume any given quantity of 

 gas should occupy under any given temperature. As it may be useful some- 

 times in experiments to know the volume a portion of gas would occupy at 

 a temperature differing from that in which the experiment is made, the follow- 

 ing formulae will be found correct. 



Let V be the volume of gas at any temperature above 32, T the number of 



degrees above that point, and V its volume at 32: then V = ( 1 + TgTj) ' hence 



; or ifVis un- 



known, it may be calculated by the formula V = , 



It frequently happens, in using Fahrenheit's thermometer, that when V for 

 the above formula is known, it is not V itself which is wanted, but the volume 

 of gas at some other temperature, as at 60 Fahr. ; this value may be obtained 

 without first calculating what V is. Let V, for instance, be any known quan- 

 tity of gas at a certain temperature, and let V" be the quantity sought at some 

 other temperature, the degrees of which above 32 may be expressed by T'. 



Now V" = - jgQ - X V ; but as V is unknown, let its value be substituted 



according to the above formula. Thus V" = ( Jgo"") X ( 480 + T) > which 



,, _ 480 a V' + 480T'V' V 480 (480 + T') V (480 + T) 



480 2 + 480 T 480 (480 + T) 480 + T ' ^uppose, for 



example, a portion of gas occupies 100 divisions of a graduated tube at 48 



Fahr., how many will it fill at 60 Fahr. ? Here V = 100 ; T = 48 - 32 or 16 ; 



i no v ^oft 

 T' = 60-32 or 28, the number sought, or the V" = -^Jg^~ = 102-42. 



This formula was given by the late Dr. Turner, in his Lectures at the 

 University of London, 1830 : see also his work on Chemistry. 



In estimating the volume of a gas, it is necessary that it be dry, as vapour 

 increases it, and the augmentation will depend upon the temperature. Dr. 

 Dalton has given a formula for the correction of moisture in gases. 



Let a = weight of 100 cubic inches of dry common air, at the pressure of 

 30 inches, and temperature 60 Fahr. ; p = any variable pressure of atmo- 

 spheric air, and / = pressure or tension of vapour in any moist gas ; then 

 the following formula? will be found useful in calculating the volumes, weights, 



