Life and Writings of Theodore de Saussure. 21 



The same air contained, after the experiment, 

 4338 cubic cent, of azotic gas. 



1408 of oxygen gas. 



of carbonic acid gas. 



5746 



" The plants have therefore elaborated, or caused to disap- 

 pear, 431 cubic cent, of the carbonic acid gas. If they had eli- 

 minated all the oxygen gas, they would have produced a vo- 

 lume of it equal to that of the acid gas which disappeared ; 

 but they have disengaged only 292 cubic cent, of it ; they 

 have, therefore, assimilated 139 cubic cent, of oxygen gas in the 

 decomposition of the acid gas, and they have produced 139 

 cubic cent, of azotic gas. 



" A comparative experiment has shewn me that the peri- 

 winkle plants which I employed weighed, when dry, before 

 the decomposition of the acid gas, 2*707 grammes, and that 

 they would furnish, by carbonisation in close vessels, 528 milli- 

 grammes of charcoal. The plants which had decomposed the 

 acid gas have been dried and carbonised by the same process, 

 and they have furnished 649 milligrammes of charcoal. The 

 decomposition of the acid gas has therefore produced 120 mil- 

 ligrammes, or 2-28 grains of charcoal. 



" I likewise carbonised the plants which had vegetated in 

 the atmosphere deprived of the acid gas, and I found that the 

 proportion of their carbon had diminished rather than increased 

 by their enclosure in the receiver.*" 



Such is the prudent and judicious method adopted by 

 Theodore de Saussure in conducting his experiments, and he 

 always continued to follow it. When engaged in the car- 

 bonisations or incinerations of plants, or the parts of plants, he 

 multiplied his precautions to such a degree of minuteness, that 

 each experiment must have occupied many days of labour, 

 alike monotonous and fatiguing. And yet he made 79 differ- 

 ent incinerations, and would have made upwards of an hun- 

 dred, had that been necessary to render the results conclusive. 

 Every one who devotes himself to scientific researches by the 

 experimental method, is aware that the difficult part of the 

 work does not consist in inventing and arranging the experi- 



