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 1\ 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 # 

 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 



