OXIDATION OF ARSENIC 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 1 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twentieth week, shows what had been expected (from unpublished 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 decrease 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 
seems to be practically without effect in modifying the rate of oxi- 
dation. This is precisely the period during which the fresh antiseptic 
should be most effective against the thinly sown and scantily nour- 
ished organisms. It can only be concluded that in recently prepared 
baths the notable oxidation which may occur is in fact not chiefly 
the result of bacterial growth but of purely chemical processes. In 
1 Department of Agriculture Bulletin 76. 
