Catalysts of Organic and Inorganic Origin. 301 



that the protoplasm is still present in the pulp cells, and very careful testing 

 shows that a trace of tannic acid may adhere to it. The colourless pulp from 

 which the sap has been removed, after pounding with water, gives distinct 

 oxidase reactions. Even after repeated extractions of pounded pulp with 

 absolute alcohol, a little tannic acid adheres to the pulp, which turns green 

 and then brown with ferric chloride, but remains colourless in air owing to 

 the destruction of the oxidase by the alcohol. Apparently, therefore, the 

 tannin vacuoles which may appear in the protoplasm are factative and are 

 due to the methyl blue or ferric chloride meeting tannic acid in the dying- 

 protoplasm. They are possibly analogous in origin to the vacuolation which 

 may be produced in dying protoplasm by various chemical agencies. Using 

 concentrated solutions of methyl blue or ferric chloride they do not appear 

 in the surface cells but only in those at a certain depth. Evidently it is a 

 condition for their formation that the cell should die slowly. 



In regard to the form of tannic acid present, this is not gallotannic acid, 

 but is more closely allied to mangrove tannin. Thus with calcium hydrate 

 it gives white turning red and not blue. As it gives green with ferric 

 chloride instead of blue or black, it is presumably a catechol yielding tannin 

 and not a pyrogallol tannin. The green given by the expressed sap or 

 pounded pulp with ferric chloride rapidly changes to brown, especially if the 

 material is nearly neutralised. Pounded pulp, allowed to brown, darkens to 

 almost black with FeCl 3 , and shows no green colour at first, but this does not 

 indicate a production of gallotannic acid by oxidation, but may be due to the 

 superposition of the two colours. 



If a dilute solution of gallotannic acid (0'05-0'1 per cent.) is divided into 

 three parts, A, B, C, and C is saturated with common salt, on adding an 

 excess of 10-per-cent. ferric chloride to B and C a green liquid is formed, 

 whereas with a drop only of ferric chloride A gives a blue-black liquid. On 

 boiling, A forms a blue-black precipitate, B forms a brown liquid, and 

 C forms a green or yellowish-green liquid. The blue-black colour reaction 

 of gallotannic acid with ferric chloride is therefore capable of various 

 modifications. 



Gallotannic acid gives a blue-black precipitate with ferric chloride in the 

 presence of oxalic acid. If ferric chloride is added to a slight excess of 

 gallotannic acid and apple sap added to the blue-black liquid, it turns green, 

 just as the sap does with EeCl3, but on standing the first liquid takes a bluish 

 tinge, while the second becomes brown. Hence, apparently, the different 

 reactions are partly due to differences between gallotannic acid and the 

 tannic acid of apple pulp and partly to the substances which accompany the 

 latter, but are not entirely due to the presence of free organic acid in the 



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