16 BULLETIN 76, U. S. DEPARTMENT OF AGRICULTURE. 
FIELD METHOD FOR -TOTAL ARSENIC." 
Since, pending further investigation, it is not possible to credit 
arsenic in the higher form of oxidation (arsenic acid or arsenates) 
with definite value as a tickicide, the efficiency of dipping baths must 
be judged for the present solely on the results afforded by the test 
for actual arsenious oxid. On the other hand, studies of changes in 
the composition of a number of dipping baths in actual service in the 
field, together with practical experience, have so far failed to show a 
clearly denned danger that the average bath, in which the strength 
of actual arsenious oxid is maintained, is likely to reach a degree of 
oxidation which may render it dangerous to cattle. Nevertheless, in 
view of obvious possibilities in these two directions, it is desirable to 
possess a field method for the estimation of total arsenic. The method 
to be described makes use of a chemical reaction recently discovered 
by the writer, 1 namely, the reduction of arsenic acid to arsenious acid 
by thiosulphuric acid. After reduction and removal of excess thio- 
sulphuric acid by iodin in acid solution, sodium bicarbonate may be 
added and the arsenious oxid, now representing the total arsenic, may 
be titrated hi the usual way. The method is necessarily more com- 
plicated, more tedious, and less accurate than the simple method for 
actual arsenious oxid. Nevertheless, rather comprehensive tests by 
representatives of the bureau in the field indicate that, if conditions 
demand such a test and no better can be discovered,, the one at hand 
will afford useful results. 
In addition to the outfit and supplies already described, the follow- 
ing supplies are necessary : 
1. ' •' Red tablets". : 
Talcum powder, U. S. P grams. . 10 
Raw potato starch do ... . 30 
Mix, and stir in 0.1 gram Sudan Red III dissolved in sufficient ether to distribute 
the color, and evaporate off ether at a moderate temperature with frequent stirring. 
Add: 
Sodium bicarbonate in fine powder grams . . 3 
Spegial soluble starch do ... . 10 
Mix, and add potassium pyrosulphate powdered to pass a 40-mesh sieve. do 125 
Mix well and compress into tablets of such size that 1 tablet will neutralize 9 to 10 
c. c. of normal alkali. The mixture, not being granulated, can not be run through the 
hopper of a power tablet machine, but must be fed by hand into the die from the table 
of the machine. 
2. "Blue tablets": 
Ultramarine blue grams . . 1 
Talcum powder, U. S. P do 5 
Sodium thiosulphate, crystallized, ground to pass 20-mesh sieve, and air- 
dried do .... 100 
Mix and compress into tablets of such size that 1 tablet will be equivalent to about 
22 c. c. of twentieth-normal iodin. 2 
1 Journal of Agricultural Research, 1914, vol. I, p. 515.. 
2 It is probable that potassium iodid should also be added in making up these tablets in order to prevent 
some oxidation of arsenious oxid by iodin in acid solution in case "oxidized arsenic" is originally present 
in amount sufficient to nearly completely use up the thiosulphate. 
