BULLETIN 259, U. S. DEPARTMENT OF AGRICULTURE. 

 Table 3. — Showing rapidity of reduction. 



No. of test. 



Per cent actual AS2O3 by analysis 



Original. 



2 days. 



11 days. 



20 days. 



a (sealed), 

 b (open) . . 



0.021 

 .021 



0.183 

 .183 



0.142 



From a consideration of the results of experiments 1,2, and 3, we 

 may derive the following conclusions: 



1. No amount of arsenic which can reasonably be used in a dipping 

 bath is sufficient notably to retard the rate of oxidation or of reduc- 

 tion, though naturally a longer time is required for the complete 

 oxidation of a large amount of arsenic than for a small amount. 



2. Under conditions favorable to reduction the action may progress 

 with extraordinary rapidity, far overbalancing any simultaneous 

 opposing action of oxidizing organisms. But in such cases the reduc- 

 ing organisms comparatively soon exhaust either their vitality or 

 the medium and thereafter are unable successfully to oppose the 

 slow but persistent action of the oxidizing organisms. 



One must proceed very cautiously in transferring any conclusions 

 drawn from such laboratory experiments to the far different condi- 

 tions which prevail in actual dipping baths in the field. None the 

 less, taking all available data from field and laboratory into con- 

 sideration, it is believed that a fairly accurate picture may now be 

 drawn of the conditions which prevail in dipping baths in actual use. 

 Suppose a vat to have been thoroughly cleaned and then charged 

 with freshly prepared bath. All the arsenic will exist in the form of 

 sodium arsenite and, if the bath be not used for dipping, will remain 

 in that form except for a comparatively unimportant oxidation 

 through purely chemical agencies. But as soon as the bath is used 

 for dipping three additions are made to it: (1) oxidizing organisms; 

 (2) reducing organisms; (3) nutrient matter upon which one or both 

 of the varieties of microorganisms can subsist. At first, of course, 

 . the number of organisms are few and the nutriment is scanty. Under 

 these conditions the reducing organisms do not thrive, but the oxi- 

 dizing organisms are able to grow to a certain extent, and thus are 

 able slowly to oxidize the bath. As further dipping is done in the 

 vat, the bath becomes richer in nutrient matter, so that the oxidizing 

 organisms flourish correspondingly and oxidize the arsenic with 

 increasing rapidity. But after a time, if dipping is done in sufficient 

 amount and at short intervals, the bath becomes so rich in nutrient 

 matter that it finally forms a favorable medium for the growth of 

 the reducing organisms, which then begin to flourish and appreciably 

 to counteract the action of the oxidizing organisms. We thereafter 



