of Determining Moisture and Carbonic Acid in Air. 325 



1832 Brunner* described a gravimetric method. He aspi- 

 rated the air at a rate of about 30 litres an hour through two 

 absorption-tubes. The first contained asbestos soaked in sul- 

 phuric acid ; and the second, which was 3 feet long, was filled 

 in the first two thirds with moist slaked lime, and in the last 

 third with sulphuric acid and asbestos. He tested the com- 

 pleteness of the absorption of the C0 2 by allowing the air to 

 bubble afterwards through baryta-solution, which remained 

 clear. The increase in weight of the first tube gave the mois- 

 ture, that of the second the C0 2 in the air aspirated. He 

 says he always obtained for free air results lying between 

 De Saussure's maximum and minimum (3*7 and 6*2 vols, per 

 10,000). 



Brunner's method, with various modifications, has been 

 used by a number of subsequent observers. The most reliable 

 results were those of Boussingault, who obtained with large 

 volumes of air a mean of 4'0 vols, per 10,000 for Paris airj. 

 The results of several other observers were certainly quite 

 unreliable. 



In 1856 Hlasiwetz \ published a paper in which he criticised 

 adversely the gravimetric method. He made a number of 

 analyses by different forms of this method, and found that not 

 only did analyses simultaneously made often entirely disagree, 

 but that in eleven out of fifty-six analyses the absorption- 

 apparatus for C0 2 actually lost in weight. These results he 

 set down partly to unavoidable "errors of weighing," and 

 partly to the fact that C0 2 is absorbed by sulphuric acid. 

 Hlasiwetz's criticisms appear to have been generally accepted 

 as conclusive ; and since the publication of his paper the 

 gravimetric method has been almost entirely given up, though 

 still described in some text-books. 



Soda-lime has for long been in use as an absorbent for C0 2 

 in combustions. It was first used by Mulder § in 1859, and 

 Fresenius || has shown its superiority to potash-solution &c. 

 Its successful use by one of us in a new form of animal- 

 respiration apparatus If suggested the working out of the 

 method described above. 



We have made experiments with a view to testing by our 



* Annalen der Physique, xxiv. p. 570. 



t Annales de Chimie, x. p. 456 (1844). 



% Sitzber. der Wiener Akad. (Mafk.-nat, A7.) xx. p. 189. 



§ Zeitschr. fur Anal. Chem. i. p. 3. 



|| Ibid. v. p. 89. 

 _ •([ A full account of this apparatus will shortly he published. A pre- 

 liminary paper on the subject was published in the ' Proceedings of the 

 Oxford University Junior Scientific Club ' for October Term, 1888. 



Phil. Mag. S. 5. Vol. 29. No. 179. April 1890. 2 C 





