12 BULLETIN 259, U. S. DEPARTMENT OF AGRICULTURE. 
his first paper Brunnich 1 found that blowing air through solutions 
of sodium arsenite produced appreciable oxidation if pine tar or cer- 
tain other substances were present, and Cooper and Freak 2 confirmed 
Brunnich' s observations. From the present experiments the power 
of tar to promote oxidation seems to be exhausted in a few weeks, 
and thereafter the progress of oxidation, in accordance with the con- 
clusions of Fuller, must be attributed to the growth of microorgan- 
isms. 
GENERAL CONCLUSIONS. 
The main conclusions already discussed in detail under the several 
series of experiments may be briefly summarized as follows : 
(1) All used arsenical dipping baths may be expected to contain 
(a) oxidizing organisms which work slowly, but steadily and persist- 
ently, and (b) reducing organisms which work very rapidly at times, 
but spasmodically. The reducing organisms exert an appreciable 
effect only in vats which are used at frequent intervals for dipping 
large numbers of cattle. The ordinary vat, used once a fortnight, 
is likely to show only a slow, steadily progressing oxidation of the 
arsenic, and periodical analyses or tests 3 must be made if proper 
dipping strength is to be maintained. 
(2) Formaldehyde solution (37 per cent), used in the proportion 
of 1 gallon to every 1,500 gallons (8j fluid ounces to 100 gallons) of 
liquid introduced into the vat, appears a safe and effective means for 
reducing oxidation to a low figure. But since there seems to be no 
evidence that under ordinary conditions oxidation is ever likely to 
progress so far as to result in the use of baths injurious to cattle, the 
question of the use of formaldehyde is purely economic. The writer 
believes tbat in most cases it will be cheaper to let some of the arsenic 
go to waste through oxidation. Wben the cost of a gallon of formal- 
dehyde about equals the cost of all the materials necessary to make 
500 gallons of dipping bath, there will probably be little financial 
gain either way, while there may be some real profit in its use through 
saving of labor in preparing dip and through the reduction of offensive 
odor from the bath by keeping it under antiseptic conditions. 
J Australian Association for the Advancement of Science, 1909, vol. 12, p. 129. 
2 Journal of Agricultural Science, 1911, vol. 4, p. 177. 
3 Department of Agriculture Bulletin 76. 
ADDITIONAL COPIES 
PF TfflS PUBLICATION MA.Y BE PROCURED FROM 
THE SUPERINTENDENT OF DOCUMENTS 
GOVERNMENT PRINTING OFFICE 
•WASHINGTON, D. C. 
AT 
5 CENTS PER COPY 
WASHINGTON : GOVERNMENT PRINTING OFFICE : 1915 
