180 ATTRACTION. 



temperature is above 32 Fahr. Then to determine its volume at 

 any other temperature, " add T | of the volume at 32, for each de- 

 gree that the temperature required, exceeds 32 Fahr. Thus, to 

 find what space 100 cubic inches of gas at 50 would occupy, if 



raised to COo _-%.4, the volume at 32, and 96.4+ 



96.4X28 = 102 the j t C0 o*_ Henry. 



480 



For pressure ; the volume of a gas is inversely as the pressure. 

 To reduce the volume to what it would be at 30 inches, the mean 

 pressure, " as the mean height is to the observed height, so is the 

 observed volume 'to the volume required. Suppose the barometer to 

 stand at 29 inches, and that we wish to ascertain what volume 100 

 cubic inches of gas would occupy at 30 inches, 30 : 29 : 1 100 : 96.66, 

 which last number is the answer required. 



For both pressure and temperature. Suppose the question is, what 

 volume would 100 cubic inches of gas, estimated at 50 of Fahr. 

 and 29 inches of the barometer occupy at 60 and 30 inches. By 

 first correcting the temperature, we find that the 100 cubic inches, 

 would be 102, and then, 30 : 29: : 102 : 98.6. 



The weight of a given volume of gas being known at any temper- 

 ature, to learn ivhat would be the weight of an equal volume at the 

 mean temperature. The volume being given, the weight will be di- 

 rectly as the pressure. Correct the bulk to the mean temperature ; 

 " then say, as the corrected bulk is to the actual weight, so is the ob- 

 served bulk to the number required." 100 cub. in. of gas weighing 

 50 grains at 50 Fahr. would at 60 occupy 102 cub. in. and 

 102 I 50: : 100 : 49.02, which would be the weight of 100 cub. in. 

 at 60. 



From the weight of a given volume of gas at an observed pressure, 

 to ascertain what would be its weight under the m,ean pressure ; say, 

 " as the observed pressure is to the mean pressure, so is the observed 

 weight to the corrected weight." 100 cub. in. of gas at 29 of the 

 barometer, weight 50, what would it weigh at 30 inches pressure. 

 29 ! 30: :50 : 51.72, the fourth term being the answer. 



To combine both the last calculations. 100 cub. in. of gas, at 50 

 Fahr. and 29 in. pressure, weight 50 grains, what would it weigh at 

 60 Fahr. and 30 inches pressure ; first make the correction for 

 temperature, which gives for the weight under a given volume, 49.02, 

 then, 29 : 30: : 49.02 : 50.71, which is the answer required, f 



* For a general formula, see Turner, 2d Ed. p. 34. 



\ These rules are cited substantially from Henry, 10th Ed. Vol. f, p. 23 



