CARBOHYDRATES. 57 



changed into carbon monoxide and oxygen. The former was believed to 

 combine with chlorophyll in much the same way as it does with haemo- 

 globin. 



Bach l has recently modified somewhat this suggestion of Baeyer. Accord- 

 ing to him, the carbonic acid is first changed into percarbonic acid, water, 

 and carbon. The percarbonic acid is then decomposed into carbon 

 dioxide and hydrogen peroxide, while" the latter forms with carbon and 

 water the formaldehyde: 



3 H 2 CO 3 = 2 H 2 CO 4 + H 2 O + C, 

 2 H 2 CO 4 = 2 CO 2 + 2 H 2 O 2 = 2 CO 2 + 2 H 2 O + 2 , 

 H 2 O + C = HCHO. 



Naturally, a great many attempts have been made to isolate formalde- 

 hyde or related compounds from plants, especially from the green leaves. 

 This has not been accomplished, however, up to the present time in a satis- 

 factory way. 2 On the other hand, nothing has been shown that is con- 

 trary to the assumption that formaldehyde does actually represent the 

 first intermediate product, for it is perfectly possible that the amount of 

 aldehyde that is constantly being formed is so extremely small that it 

 condenses so rapidly that it escapes detection. It has been brought 

 forward in support of Baeyer's theory that certain plants show a con- 

 siderable resistance towards formaldehyde. Thus Treboux 3 found that 

 Elodea canadensis will stand a 0.001 per cent solution. Algae and young 

 plants of Sinapis alba are said to be strikingly resistant towards formal- 

 dehyde. 4 



We saw in considering the artificial synthesis of carbohydrates that 

 it was possible to form a sugar very easily from formaldehyde, and we 

 can readily understand how, according to the number of molecules of 

 formaldehyde entering into the reaction, sugars containing a different 

 number of carbon atoms in the molecule may be obtained. It is, how- 

 ever, scarcely probable that such syntheses take place in this simple way. 

 Thus, for example, according to all that we know at present, it is hardly to 

 be expected that pentoses are formed directly as one of the first products 

 of the condensation of formaldehyde. Apparently it is much more likely 

 that such sugars are formed by the breaking down of higher sugars 

 especially the hexoses. Such a process is likewise easy to represent, as, in 



1 Arch. sci. phys. nat. Gen. 5, 401 (1898). 



2 H. Euler: Ber. 37, 3411 (1904). Hans and Astrid Euler: Arkiv for Kemi. 1, 347 

 (1904); Ber. 39, 39 (1906), and ibid. 39, 45 (1906). W. Loeb: Z. Elektrochem. 11, 745 

 (1905). 



3 Trehoux: Flora, 73 (1903). 



4 R. Bouillac: Compt. rend. 135, 1369 (1902). Bouillac and Giustiniani: ibid. 136, 

 1155 (1903). 



