12 BULLETIN 259, U. S. DEPARTMENT OF AGRICULTURE. 



his first paper Briinnich 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 (8| 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 that in most cases it will be cheaper to let some of the arsenic 

 go to waste through oxidation. When 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. 



1 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. 



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