4 64 Description of a Manometer. 



The column of mercury sustained by the elastic vapour 

 which was produced during the experiment, 



= O m .003ll. 

 The manometer brought to the primitive data has therefore 

 undergone a decrease 



= ,n .050 •+ n, .0O864 + n, .00311 =s O m .06)75, 



= 0.0813 of the volume of air used in the experiment. 



In order to know on what substance the absorption acts, 

 we must keep an account of the quantity of carbonic acid 

 which ought to be dissolved; and as we have neglected to 

 do it by precipitation, as I have indicated, we shall confine 

 ourselves to regard, with M. de Saussure, this quantity as 

 equal in volume to the liquid. 



The capacity of the manometer being four litres 676, the 

 volume of the liquid = 0,565, the volume of the air in the 

 experiment = 4 lit. Ill, the volume of the carbonic acid 

 dissolved by the liquor = lit. 565 y forms the 0,137 : now 

 on adding up the proportionsof carbonic acid and of oxygen 

 formed in the air, and supposing that the oxygen gas on 

 combining with the carbon is replaced by a volume of car- 

 bonic acid precisely equal to its own, we find that there 

 is wanting in 100 parts of air 10,54 of oxygen, or the 0,105 

 of the volume of the air, a quantity which only differs 

 0,032 from that of the carbonic acid which has been sup- 

 posed to be dissolved by the liquid. This difference ought 

 to be neglected, because the volume of the carbonic acid 

 absorbed ought to be inferior to that of the water, either on 

 account of the elevation of temperature, or on account of 

 the diminution of the pressure. 



If we compare this result with the preceding indication 

 of the manometer, we find that there is only 0,02 of dif- 

 ference, a quantity which may be neglected, chiefly on ac- 

 count of the inaccurate valuation of the carbonic acid held 

 in solution. 



The phaenomena, therefore, answer perfectly in this cir- 

 cumstance to the observations of M. de Saussure; the oxy- 

 gen gas is not absorbed by the decoction of campeachy ; but 

 the latter changes it into carbonic acid, on giving up car- 

 bon to it : at the same time, without doubt, water is 

 formed by the intimate union of the oxygen and hydrogen 

 which existed in the substance, which thereby becomes 

 more carbonized; and it is by these effects that we ought to 

 explain the alterations which it undergoes in its properties. 



Then this solution gives only a yellow precipitate with 

 the nitro-muriate of tin, instead of a bright red precipitate: 



an 



