ASSAY OF ARSENICAL DIPPING FLUIDS. 11 
tionally that a laboratory method can be modified so that it is of 
any practical use whatever in the field, and in any event it is almost 
certain to lose something in accuracy. One thing is absolutely 
essential, that the field operator shall follow the instructions given 
him to the minutest detail, no matter how irrelevant or unimportant 
they may appear to him. 
FIELD METHOD FOR ACTUAL ARSENIOUS OXID. 
The field method at present employed by the bureau for actual 
arsenious oxid is simply an adaptation of laboratory method "A" 
for the same substance. The outfit is pictured in figure 1, and each 
part composing it will be described in detail. 
(1) The case. — The carrying case for the outfit is a rectangular box 
with a hinged cover, made of five-sixteenths-inch oak, of inside dimen- 
sions 7 J by 5 J by If inches. The interior partitions, of thinner and 
softer wood, are sufficiently indicated in the diagram. The case 
must be strongly mortised or nailed together, not simply glued, and 
should be varnished inside and out. 
(2) The utensils. — Bottle A', fitting into compartment A of the 
case, is an ordinary 3-ounce wide-mouth bottle of clear glass. 
Measuring cylinder C, fitting in compartment C, is of ordinary 
type, of 25 c. c. size, graduated to half cubic centimeters. Preferably 
the figures indicating the graduations read down only. C" is a bristle 
swab for cleaning. It will be noted that the partitions of compart- 
ment C are cut away at the bottom to admit the foot of the cylinder. 
At the point p on the back wall of the case is fastened a quarter-inch 
pad of cork to protect the cylinder from breakage. The swab C" is 
put into compartment C after the cylinder, thus protecting the latter 
from breakage on that side. 
(3) The reagents. — The iodin solution, or, as it is termed for field 
use, the "test fluid," is contained in bottle D', a 4-ounce standard- 
shaped " sample oil" bottle, preferably of amber glass and provided 
with a "flat-hood" glass stopper. A half -inch ring of the If -inch 
(measured flat) thin rubber tubing, manufactured for use with Gooch 
crucibles, is drawn over the shoulder of the bottle, cemented in place, 
and coated with collodion. At the bottom of compartment D is 
fastened by a screw a conical spiral spring, the upper whorl of which 
is large enough to inclose the bottom of the bottle. In placing the 
latter in the case the bottom is inserted in the whorl of the spring 
and the bottle then pressed down until it slides into place. The 
partition between C and D is cut away in a semicircle at the point q 
to allow the fingers easy access to the bottle when it is to be removed. 
The test fluid is of such strength that in the actual performance 
of the test each cubic centimeter of it employed represents exactly one 
