US Geological Survey Bulletin 2144 18 Elements Table 2

Determination of 18 Elements in 5 Whole Argonne Premium Coal Samples by Quantitative Direct-Current Arc Atomic Emission Spectrography

Table 2. Equipment and operating conditions for direct-current arc atomic emission spectrography.

[A, ampere; ASTM, Amercian Society for Testing and Materials; dc, direct current; min, minute; s, second; T, transmission; V, volt.]

Subject	Group I, involatile elements	Group II, volatile elements
Sample	100 mg pulverized whole coal mixed with 100 mg Li2CO3 powder (American Potash) and 50 mg graphite powder (-200 mesh, Ultra Carbon); 25 mg of mixture tamped into anode cup.	100 mg pulverized whole coal mixed with 100 mg Li2CO3 powder (American Potash) and 100 mg graphite powder (-200 mesh, Ultra Carbon); 50 mg of mixture tamped into anode cup.
Spectrograph	Ebert mounting, 3.4-m focal length, 0.5-nm/mm reciprocal linear dispersion in first order. Grating: 600 grooves/mm, blazed for 300 nm.	Eagle mounting, 3-m focal length, 0.55-nm/mm reciprocal linear dispersion in first order. Grating: 590 grooves/mm, blazed for 300 nm.
Slit	25 m 2 mm for spectra from standards and samples; 25 m 4 mm for spectra from iron arc.	25 m 2.5 mm for spectra from standards and samples; 25 m 5 mm for spectra from iron arc.
Wavelength range	240-360 nm, first order	250-340 nm, second order.
Illumination	Arc image focused on collimator mirror by a 450-mm focal length cylindrical quartz lens located at the entrance slit.	Arc image focused on grating by a 450-mm focal length cylindrical quartz lens located near the entrance slit.
Filters	Neutral density, 35% T plus 75% T, for exposures of samples and standards. Two-step neutral- density filter, 40% T: 100% T, for iron arc exposures used in calibration of the photographic emulsion.	None for exposures of samples and standards. Two-step neutral-density filter, 50% T: 100% T, for iron arc exposure used in calibration of the photographic emulsion.
Electrodes	Cathode: Graphite rod (Ultra Carbon no. 5001) 3.2 mm in diameter and 3.8 cm long . Anode: Thin-walled graphite electrode (Ultra Carbon no. 1590) 3.6 mm in diameter.	Cathode: Same as for group I. Anode: Graphite electrode (Ultra Carbon no. 3170) 5.7 mm in diameter .
Excitation	Arc current: Stepped arc current, 5 A dc for 10 s, 15 A dc for 95 s, across constant 4-mm arc gap. Voltage source of 300 V, open circuit. Electrode supporting the sample is the anode. Atmosphere: 80% Ar, 20% O2; 6.6 L/min through Helz jet (Helz, 1964).	Arc current: Stepped arc current, 8 A dc for 10 s, 25 A for 110 s, across constant 4-mm arc gap. Voltage source of 300 V, open circuit. Electrode supporting the sample is the anode. Atmosphere: Ar, 6.6 L/min through Helz jet (Helz, 1964).
Photography	Eastman-Kodak III-0 emulsion on 101- 254-mm glass substrate. Emulsion was processed in Eastman-Kodak D-19 developer for 3 min (20C), short stop solution for 30 s, and fixer for 10 min. Then, the plate was washed in tap water for 10 to 20 min, allowed to drain, and dried with warm air for 5 min.	Same as for group I elements.
Microphotometry	All microphotometry was done by conventional methods, such as those described by ASTM (ASTM, 1971, p. 79-80).	Same as for group I elements.