Decembek 29, 1911] 



SCIENCE 



925 



Gore, of the Bureau of Chemistry, U. S. De- 

 partment of Agriculture, that the use of any 

 " inert " gas would be equally efficient, and 

 accordingly he tried the effect of carbon diox- 

 ide (Gore, 1910, 1911). The outcome of his 

 experiments, as of my own (Lloyd, 1911) is to 

 show that the results of Japanese method of 

 processing, a procedure, apparently empirical, 

 of exposing the fruit to the fumes of sake 

 by packing in recently emptied casks, may 

 be duplicated. Indeed, according to Fair- 

 child (1905, 1911), attempts on a limited scale 

 to imitate the Japanese method in this coun- 

 try, had already met with success, so that 

 there could have been little doubt in the 

 minds of those cognizant of the facts that, 

 with effort, but a short time need intervene 

 before a method could be worked out for at- 

 taining, even on a practical scale, the results 

 desired. The expectation must have been 

 strengthened by the results obtained by Vin- 

 son (1909) on the date (Phoenix dactylifera) 

 whose fruit possesses, as regards the tannin 

 cells, cytological characters precisely similar 

 to those of the persimmon, sapodilla and other, 

 doubtless numerous, fruits. Vinson found 

 that acetic acid fumes can be used for pro- 

 cessing dates to prepare them for the market, 

 the immediate and important outcome being 

 the loss of astringency. He (Vinson, 1910) 

 further found that a host of reagents of the 

 same phase can be used, but with attendant 

 results undesirable from an economic point of 

 view. Of these, for a single example, nitrous 

 ether affects the tannin cells in such a man- 

 ner that the contained tannin is no longer 

 free to enter into solution, and hence the non- 

 astringency. Even heat may be used to 

 hasten the result, as Vinson (1907, 1910, 

 1911) also showed, while Freeman (1911) ex- 

 tended the use of this discovery in a practical 

 way. 



In order to describe the loss of astringency, 

 it was stated jointly by Bigelow, Gore and 

 Howard (1906) and later by Vinson (1907) 

 that the tannin in the persimmon becomes 

 " insoluble " during the ripening process. 

 But, as I have shovm, " insoluble " tannin is 

 not otherwise known. To use the adjective 



quoted is to contravene the accepted defini- 

 tions of the substance therewith described. 

 Indeed, the astonishing unusualness of the 

 conception appears when it is realized that 

 there is known no compound of tannin with 

 organic products, composing " leather " of one 

 form or another, which, by repeated contact 

 with fresh solvent, will not give up fractions 

 of the amount of tannin originally bound up 

 with the associated substance. Analogies in 

 the field of colloidal chemistry will immedi- 

 ately occur to those even only slightly initiated 

 into its mysteries, for such they surely are at 

 the present moment. My own work begun on 

 the date (1910) in 1907 and continued on the 

 persimmon (1911, a and h) and sapodilla 

 (1911, 5) has enabled me to throw some light 

 on the difficulty. I have shown that, during 

 the process of ripening, the loss of astringency 

 is due to the union of the tannin with an as- 

 sociated colloid (1911, a) of- carbohydrate na- 

 ture (1911, 6), which is an intraprotoplastic 

 product in common with the tannin itself, and 

 which undergoes a gradual coagulation as 

 seen in its increasing firmness and loss of 

 swelling capacity. During this process the 

 tannin becomes adsorbed, and there is thus 

 formed a vegetable leather, from which only 

 exceedingly small fractions may be extracted 

 by ordinary solvents (water, alcohol), but 

 which may be attacked chemically and then 

 extracted by means of strong nitric acid, 

 leaving the entire, or nearly the entire amount 

 of the associated colloid intact (Lloyd, 

 1911, c). We may thus obtain this as yet 

 practically unknown body for examination by 

 chemical methods, which have already yielded 

 some important results, indicating as above 

 noted its carbohydrate nature. 



So that it develops that the essential fact 

 of the loss of astringency is the formation of 

 a colloidal complex, of which tannin is one, 

 and another carbohydrate the other member. 

 Disregarding those reagents which have a 

 chemical effect upon the tannin itseK (so far 

 as we can determine this) there is a number 

 of substances which are capable of hastening 

 this process. Alcohol and acetic acid vapors 

 (the possible chemical effect of the latter on 



