DECOMPOSITION OF CARBONIC ACID. 37 



in order that the absorption of carbonic acid, which must, of course, 

 take place, might be thrown out of ihe reckoning. The experiment 

 was continued for six days, during which the plants received the 

 direct rays of the sun from five to eleven o'clock in the morning. 

 On the seventh day, the plants were withdrawn. They had pre- 

 served their freshness. All the corrections made for temperature 

 and pressure, the volume of the atmosphere in which they had lived 

 was not found changed by more than about 20 cubic centimetres, 

 7.8 c. in., a quantity which is within the possible errors of compu- 

 tation ; but the composition of the air had undergone very notable 

 changes : the carbonic acid had disappeared, and the eudiometer 

 proclaimed 0.24 of oxygen instead of the 0.21 which it contained 

 originally.* 



RESULTS OF THE EXPERIMENTS. 



c. inches. Azote. Oxygen. Garb. acid. 



Pe/ore : Volume of atmosphere 2257 containing 1650 438-5 169-3 



^fter: " " 2257 " 1704 553 0_^ 



+54 +14-8 —169-3 



The periwinkles, consequently, had caused 169.3 cubic inches of 

 carbonic acid to disappear, and given off upwards of one hundred 

 and fourteen cubic inches of oxygen. Had the whole oxygen of the 

 carbonic acid been set at liberty, this volume would have been pre- 

 cisely equal to that of the acid gas decomposed ; but as no more 

 than one hundred and fourteen cubic inches of oxygen were obtained, 

 it must be inferred that the periwinkles had fixed 54.6 cubic inches 

 of this gas. 



This is the conclusion, indeed, to which M. de Saussure came, 

 and subsequent experiments have confirmed its accuracy. The 

 following table contains a summary of five experiments that were 

 instituted : 



C. inches. c. inches. 



Exp.l. Carbonic acid disappearing. ••169.3 Oxygen disengaged.. • 114-7 



Azote disengaged- •• • • 54-6 

 169-3 



Exp. 2. " " " •••121.4 Oxygen disengaged. . . 88 



Azote disengaged • • • • 33 

 121 



Exp. 3. " " " ....58-5 Oxygen disengaged — 47.5 



Azote disengaged 8-2 



55.7 



Exp. 4. " " " ...120-2 Oxygen disengaged — 96-6 



Azote disengaged . . . .. 7-8 



104.4 

 Exp.5. u u u ....72.3 Oxygen disengaged.... 49.5 



Azote disengaged 22.4 



There is one remark which it is impossible to avoid making in sur- 

 veying this table ; it is to the effect, that the azote disengaged rep- 



* Saussure, Kccherches chimiques, p 40 

 4 



