Life and IFritmgs of Theodore de Saussure. 29 



coal, enclosed in pure oxygen gas, entirely converted it into 

 carbonic acid, — an interesting fact, in as much as it explains the 

 gradual destruction and conversion into a fertilising principle of 

 vegetable soil and other carbonaceous matters left by the de- 

 composition of organised beings. 



In the second section of his work, Theodore de Saussure 

 examines the results presented by the absorption by porous 

 bodies of several gases combined. Sometimes he impregnated 

 the body with one gas and introduced it into another ; some- 

 times the porous body was placed in the mixture entirely 

 formed of gases. In the former case, one part of the gas with 

 which the body is impregnated issues from it to give place 

 to a new one ; producing sometimes an augmentation of the 

 atmosphere, causing cold; at other times, heat, with a di- 

 minution of the volume of the gas ; according as the new gas 

 is susceptible of a greater or less condensation than that which 

 had preceded it. A portion of the primitive gas always re- 

 mains in the porous bodies, and the presence of a new gas 

 often brings on a somewhat greater condensation ; but there 

 is never a combination of the two gases in the charcoal, as, for 

 example, the formation of water in a mixture of hydrogen 

 and oxygen, the production of ammonia in the hydrogen and 

 azote, &c. 



In the third section, he examines the absorption of gases by 

 liquids ; and he found that the latter, like solids, present great 

 differences in the order according to which they condense them; 

 and that these absorptions are, in consequence, subject to the 

 laws of chemical affinity. In general, except in cases of very 

 strong affinity, such as that of water for ammonia and muri- 

 atic acid, where the absorption is 780 and 516 times its volume, 

 the porous bodies condense more gas than liquids do. He then 

 examines the influence exerted on the absorption of gases by 

 viscosity, which he finds to have no effect ; and afterwards 

 that exercised by pressure, as well as the phenomena resulting 

 from the simultaneous or successive absorption of different 



The great importance which Theodore de Saussure had at- 

 tributed to carbonic acid in the nutrition of vegetables, must 

 have naturally drawn his attention to the proportion of this 

 gas existing in the atmosphere. In 1816, he inserted in the 



