OXIDATION OF AESENIC IN DIPPING BATHS. 11 



experiments which are not within the province of the writer have 

 settled this point. It is of interest to note that a layer of oil will 

 almost entirely prevent evaporation of water from the bath. 



(2) Cresylic acid in admissible amounts only partially inhibits the 

 growth of oxidizing organisms, a conclusion borne out by practical 

 experience with proprietary dips containing that substance. 



(3) Formaldehyde solution is a powerful and effective antiseptic 

 against both classes of organisms, and inasmuch as it does not inter- 

 fere with analytical methods for the determination of arsenic, it is 

 appropriate as a preservative of samples of bath taken from a vat for 

 chemical analysis, as recommended elsewhere by the writer. 1 



Similar experiments were tried on some other antiseptics, espe- 

 cially those which would not interfere with analytical estimations of 

 arsenic. Nothing was found, however, which at all approached 

 formaldehyde in effectiveness and general applicability. 



FIELD EXPERIMENTS OF 1914. 



The experiments of 1914 were directed toward determining the 

 efficacy and practical applicability of formaldehyde as a preservative 

 against oxidation of dipping baths in the vat. Three vats were 

 selected which were expected to be closely comparable in degree of 

 usage, etc. One of the vats received no addition of formaldehyde 

 and thus served as a check. The samples taken from the vats were 

 further treated with formaldehyde and shipped in sealed bottles, 

 while methods of analysis * had by this time been thoroughly worked 

 out. The analytical results of this series of experiments were very 

 accurate, but are nevertheless best presented in the form of dia- 

 grams as in the case of the dipping experiments of 1913, no further 

 explanation of the diagrams accordingly being necessary. 



The diagram for vat I is very characteristic. Vat K, up to the 

 twentieth week, shows what had been expected (from unpublished 

 data) might occur if too little formaldehyde were used, namely, that 

 the reducing organisms are more sensitive to it than are the oxidizing 

 organisms, so that too little formaldehyde is worse than none at all. 

 Vat J, as well as vat K after the twentieth week, shows that a suffi- 

 cient amount of formaldehyde does decidedly decreaso the extent to 

 which oxidation progresses, especially after the vat has been in use 

 for a few weeks, but for the first four to six weeks formaldehyde 

 ms to be practically without effect in modifying the rate of oxi- 

 dation. This is precisely the period during which the fresh antiseptic 

 should be mosl effective against the thinly sown and scantily nour- 

 i h< d organi ms. It. can only be concluded that in recently prepared 

 baths the notable oxidation which may occur is in fact not chiefly 



the resull of bacterial growth but of purely chemical processes. In 



1 Department of Agriculture Bulletin 76, 



