118 COMPRESSIBILITY OF GASES. 



BEGNAULT 1 — 1841 . 



Twelve years later this conclusion was overthrown by 

 the classic experiments of Victor Regnault. Regnault' s 

 method and apparatus were in principle essentially those 

 of Dulong and Arago, surpassing them and all others, 

 however, in the refinements introduced for the purpose 

 of banishing or correcting those troublesome sources of 

 error which hitherto had perplexed the judgment of all 

 observers. These errors were 



First, Moisture in the air operated on, which would 

 cause it to seem more compressible than it really is. 

 Regnault provided an efficient system of absorption tubes 

 by which every trace of vapor could be removed. 



Second, Heat generated in the air by its own compres- 

 sion, which would reduce its observed compressibility 

 below the real value. Regnault enclosed his air tube in 

 a jacket, through which a stream of water flowing kept, 

 a constant temperature as shown by a delicate ther- 

 mometer. 



Third, Variations in the temperature of the mercury 

 in the pressure-column during the experiments, which 

 would cause the same length of column to contain differ- 

 ent weights of mercury, exerting a greater pressure if 

 colder and a lesser pressure if warmer. Regnault placed 

 thermometers at intervals along the pressure column, ob- 

 served the actual temperature, calculated the error and 

 corrected the observed height of the column accordingly. 



Fourth, Compressibility of the mercury itself due to 

 its own weight, which would diminish the height of the 

 pressure column and reduce the observed pressure below 

 the actual value. Regnault calculated this compressi- 

 bility in every instance, and made the proper corrections 

 for it. 



1 Memoires de l'Acadernie des Sciences, torn, xxi— (Original.) 

 Cooke's Chem. Physics, p. 296— (a table.) 

 Deschanel Natural Phil., Everett — p. 173— (Apparatus.) 



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