Electrical Ignition in the Schoniger Oxygen Flask Method A. J. Martin' and Harold Deveraux, Polychemicats Department, E. 1. du Pant de Nemours & CO., Wilmington, Del.
the conventional Schoniger proI cedure] the filter paper is ignited by N
a n open flame, after which the adapter is inserted quickly into the flask containing oxygen [Mikrochim. Acta 1955 (l), 123; 1956 (4-6), 8691. When handling some materials, particularly those which may be thermally unstable, ignition by electrical means may be more convenient, safe, and reliable. This permits the whole operation to be carried out in a closed system. Apparatus. The adapter used in t h e authors' laboratory is shown in Figure 1. It consists of a ground-glass joint cemented with Sauercisen cement (No. 31 binder, N o . 31 filler) onto a 2-inch length of copper tubing, 1 inch in outside diameter. T h e mesh basket for holding the filter paper with the sample is made of 22-gage platinum wire. The support rods and ignition filament are of 18- and 30-gage platinum wire, respectively. The electrical ignition system consists of a double-pole, singi.+throw push hutton switch on the primary winding of a 6.3-volt, %ampere filament transformrr. The secondary circuit has a l-ohm, 25-watt variable resistor to limit the current to the ignition filament. A Parr ignition unit, as used with the Parr oxygen bomb, is also satisfactory, if the appropriate filaments are used in the adapter. This adapter was designed for use with the safety shield shown in Figure 2. An aluminum stand (0.25 X 2 inches) is fitted with an aluminum skirt (16 gage) and a window of 0.25-inch acrylic resin is pivotted a t the ccnter as shown in the figure. Procedure. The sample is folded into the filter paper flag in t h e usual manner and placed in t h e wire basket with the stem of the flag drawn into the V of the filament i+ire. T h e adapter is inserted into the ground glass joint f grind of a !250-, 500-, or 1000-ml. flask containing oxygen and thc scrubbing solution. The copper
I Present address, F & Corp., Wilmirigton, Del.
1932
RI Scientific
ANALYTICAL CHEMISTRY
-PLATINUM
M E S H BASKET
PLATINUM F I L A M E N T PLATINUM S U P P O R T S
COPPER WIRE L E A D S
COPPER T U B l U G
E R E I S E N CEMENT
Figure 1.
Adapter
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tube is inserted into the flask support and spring leashes are attached to ears on the flask. Then the window is rotated, placing the flask behind the window and inverting it t o produce a liquid seal at the joint. The push button on the ignition system is depressed until the filter paper begins to burn. After the flame is extinguished, the window is rotated to the previous position and the adapter is removed from the support without opening the flask. If necessary, the flask is shaken vigorously or allowed to stand in order to scrub the combustion gases. The shield is sufficiently sturdy to find use in many laboratory operations. Its ability to withstand explosion was tested by setting off a blasting cap in a 1@)O-ml.flask held in the shield. The acrylic winc'Qw and the aluminum skirt were scratched by flying glass, but no major damage occurred t o the shield. No glass fragments were projected past the front part of the shield. Thc analytical results obtained with the apparatus and procedure described have compared favorably with those found by using hand ignition.
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Figure 2.
Safety shield for use with Schoniger oxygen flask technique
