246 



NATURE 



\ya71. 29, 1874 



and hydrogen. It can reduce carbonic acid to oxygen 

 and oxide of carbon, just as happens in the green parts 

 of plants under the rays of the sun. 



As we learn by experiment that for one volume of 

 carbonic acid decomposed by the green parts of plants, 

 one volume of oxygen is given off, i.e. one volume of 

 oxygen exactly equal to that of the carbonic acid, the 

 decomposition of the latter being only partial, it is 

 necessary that the water be forcibly decomposed in the 

 same time as the carbonic acid, and that it yield us the 

 half volume of oxygen necessary to complete that which 

 appears at the moment of insulation, so that the de- 

 composition is represented as follows : — 



I vol. carbonic acid = i vol. carbonic oxide + .' vol. oxygen. 

 I vol. vapour of water = i vol. hydrogen + i vol. oxygen. 



The disengaged oxygen presents then a volume equal 



to that of the decomposed carbonic acid, and leaves 

 instead carbonic oxide and hydrogen in equal volumes, 

 which, on uniting, furnish in vegetables one of the products 

 that are met with in young plants, glucose, which exactly 

 represent the carbonic oxide and hydrogen, or, again, 

 the carbon and the water. But this product has never 

 been directly prepared ; it has been impossible, so far, 

 to obtain it by synthesis, and all the attempts to unite the 

 carbonic oxide to the hydrogen have been futile. There 

 is, however, a problem of the same order which has 

 been solved by MM. Thdnard, and, in our opinion, is 

 one of the most important points of their recent labours. 

 They have not obtained, it is true, the organic matter, 

 yet without a name, which was condensed upon their 

 tube by directly combining hydrogen and the carbonic 

 oxide, but by employing carbonic acid and formic acid. 



in which the elements are met with in the same propor- 

 tions, in fact, instead of having 



2 vols, cailionic oxide con- \ I vol. oxygen, 



taining ( I \ol. caibon vapour. 



2 vols, hydrogen, 

 they have employed 



4 vol. carbonic acid, con- ( 4 vols, oxygen, 



taining I 2 vols, carbon vapour. 



4 vol. carburetted hydrogen \ 2 vols, carbon vapour, 



containing j S vols, hydrogen. 



in which the oxygen and carbon, as in the first case, are 

 in equal volumes, and the hydrogen in double volume. 

 We may then regard the experiment of M. Thenard as 

 opening a new way to the synthesis of organic sub- 

 stances, already so brilliantly studied by M. Berthelot. 



The first apparatus employed by MM. Thdnard pre- 

 sented a drawback ; the gases circulated with considerable 

 difficulty, and their union was not so complete as could be 

 desired; they could not easily be renewed. MM. Thdnard 

 have got rid of this difficulty by means of the apparatus 

 represented in Fig. 2. It will be seen that the electricity 



from the coil is distributed in the two tubes by cups filled 

 with chloride of antimony, one forming the external tube, 

 the other the interior, between which circulate the gases. 

 These are kept in continuous motion by means of a 

 very ingenious employment of mercury. By examin- 

 ing the figure it will be seen that the mercury placed 

 in the large vessel, firmly fixed above the apparatus, can 

 be let out drop by drop into the vertical tube on the right 

 and carry along a certain quantity of gas imprisoned 

 between two consecutive drops. The excess of mercury 

 falls back into the vat into which the horizontal tube 

 goes, while the moving gas received into a funnel which 

 dips into the mercury, is brought into the annular space 

 where it is subjected to the effluvia. 



It is thought that if the gases in coalescing yield 

 a liquid or solid substance, which can only happen 

 by a great diminution of volume, it may be possible to 

 introduce through the funnel placed under the mercury, a 

 new proportion of the gases which, under the influence 

 of the diluvium, will react upon each other. 



