RECENT ADVANCES IN SCIENCE 371 



as catechol, quinol, pyrogallol, gallic acid, quercetin, chrysaro- 

 bin, etc. ; all these bodies take up oxygen and yield hydrogen 

 peroxide in the presence of water, and can only reduce in the 

 presence of oxygen, whereas in the case of the sugars the 

 necessary oxygen is supplied by the sugar molecule itself. Some 

 of the polyhydric compounds mentioned can make the complex 

 themselves out of ferric hydroxide, but not all of them, as, 

 for example, phloroglucinol, which can only produce it from 

 potassium ferricyanide. It is not necessary for the autoxidis- 

 able compound to be part of the iron complex since, for ex- 

 ample, the iron complex may be applied with catechol carboxylic 

 acid. It is interesting to note that these autoxidisable sub- 

 stances, which are widely distributed in nature, may act in 

 the presence of oxygen either as oxidisers (e.g. converting 

 methylalcohol to formaldehyde), or as reducers, converting 

 nitrites in presence of complex iron into ammonia. 



The formation of nitrites from nitrates in aqueous solution 

 forms the subject of a paper by Moore (Proc. Roy. Soc. 191 8 [b] 

 90, 158). Rain water which has been kept for some time 

 contains only nitrates, as all nitrite has been oxidised ; if, 

 however, such rain water is exposed to sunlight a marked nitrite 

 reaction can be obtained from it ; but if leaves are immersed 

 in the solution very little nitrite accumulates. In the author's 

 opinion nitrites which are more active than nitrates are formed 

 from the latter on the green leaf exposed to sunlight, and form 

 the first stage in the synthesis of nitrogenous compounds. 



Willstatter and Schudel (Berichte, 191 8, 51, 781) describe a 

 new method of extracting organic colouring matters from 

 aqueous solution by means of organic solvents. It was shown 

 some time ago (Annalen, 1916, 412, 1 13-231) that plant pig- 

 ments could to a certain extent be extracted by a process , 

 depending on the partition of the pigment between water and 

 amylalcohol. Only non-glucosidic pigments could, however, be 

 extracted efficiently by this process, the glucosidic ones remain- 

 ing in aqueous solution. By adding picric acid to the solution, 

 however, a larger number of pigments become amenable to 

 extraction, as picrates, especially if a mixture of amylalcohol 

 (2 parts) and acetophenone (1 part) is used. It is now found 

 that dichloropicric acid is preferable to picric acid, since the 

 compounds which it forms with dyes are more frequently 

 soluble in organic solvents. Thus in presence of dichloropicric 



