30 Professor Macaire on the 



first volume of the Bibl. Univ. certain researches on this sub- 

 ject, researches which he afterwards multiplied and completed ; 

 and which form the subject of a memoir which he published 

 in 1830, in the Memoir es de la Societe de Phys. et d'Hist. 

 Nat. de Geneve. 



The process which he preferred as a means of estimating 

 the quantity of carbonic acid contained in the air at a given 

 moment, consists of pouring barytic water into a large globe 

 slowly filled with the air we wish to examine, after having 

 first emptied it by means of the air-pump. We then take the 

 temperature of the air enclosed in the vessel, and that of the 

 external air ; then observe the hygrometer, barometer, the 

 wind and clouds ; account is also taken of the state of humidity 

 of the soil, and of the season. The stop-cock is then closed, 

 and it is shaken for an hour, after which it is left at rest for 

 eight days, only shaking it from time to time. The carbonate 

 of barytes produced is then collected ; it is washed in distilled 

 water saturated with carbonate of barytes ; we then decant into 

 a jar ; the containing vessel is seven times washed with greatly 

 diluted muriatic acid, and after having half evaporated this 

 solution, it is made use of to dissolve the carbonate of barytes 

 formerly obtained. This solution is precipitated by means of 

 sulphate of soda ; the sulphate of barytes produced is decanted, 

 washed, dried, and weighed, and we thence infer the weight of 

 the carbonate of barytes which is formed in the first operation, 

 that is to say, the quantity of carbonic acid in the air. The 

 analysis of the same air, made at the same place, and repeated 

 six times, has given differences which run from 4'12 to 3*89. 

 If we add to these long, troublesome, and monotonous pro- 

 ceedings, a multitude of precautions in matters of detail, which 

 I suppress, and which were repeated at every analysis, we can 

 understand what perseverance and patience Theodore de Saus- 

 sure required to repeat them on 225 different occasions, most 

 frequently at Chambeisy (a country house about a league from 

 Geneva), sometimes on the lake at Geneva, as well as on dif- 

 ferent mountains, the Saleve, the Dole, the Jura, &c. These 

 numerous materials once united and compared, a summary 

 of Theodore de Saussure's conclusions may be given in a few 

 words. 



The mean of the carbonic acid of the air is, at Chambeisy, 4*15 



