ferred by many workers, in the alkali melt of a glass fusion. A secondary consideration, in the choice of this melt formula, was the physical nature of the cooled melt. Pyrosulfate melts are extremely hard and tough and require special handling equipment. The melt from the formula we adopted was easily handled and efficiently ground in a standard mortar and pestle. We attempted a spark technique on these melts after dilution with a variety of carbon and graphite diluents as suggested by Hargis and Smith. Unfortunately, we could not obtain results similar in precision and accuracy to those which Hargis and Smith had reported. Howeyer, the same melt formula, diluted properly with graphite, and excited in a D C arc system, gave significantly improved analytical results. EXPERIMENTAL
Sample Preparation. A 100-mg. sample, ground to pass a 100-mesh sieve, is fused in a 30-ml. platinum crucible with 2 grams of potassium
carbonate, 2 grams of sodium carbonate, and 25 mg. of sodium bismuthate. The fusion product is transferred to a mortar by inverting the crucible and lightly tapping the bottom, then grinding to a fine powder. A 200-mg. portion of the ground melt is diluted with an equal amount of graphite powder (non-pellet-forming grade). The mixture is shaken vigorously for 1 minute on a mechanical shaker. A weighed portion, 7.5 mg., is transferred to an undercut, cupped electrode (Yational L-4006, Ultra 105-S or equivalent) and arced a t 7.5 amps. for 20 seconds. Seutral filters are used to control the amount of light passing through the 50-micron slit so that the analytical line (Pb 2873.3) a t 24% PbO gives a densitometric value of 30 to 40 and also the internal standard line Bi 2898.0 gives a similar densitometric reading. A background correction was not used or required. Standard samples are prepared in a similar manner.
line working curves. A variety of lead crystal samples from different sourcesPoland to England--were analyzed by this procedure and by wet procedures. Table I is a tabulation of the results obtained. Table I1 is a tabulation of the precision data found. iI7e believe that our spectrochemical procedure is suitable for lead glass containing 20 to 30% lead as PbO. We have intentionally arranged the parameters in this procedure to simplify and to improve the spectrochemical analysis technique for lead crystal. It may be suitable for PbO ranges of lead content outside the 20 to 30% PbO range but we have not had the need to develop this information LITERATURE CITED
(1) Hargis, D. C., Smith, G. W., ANAL. CHEM. 36,824 (1964).
ALVIXBOBER
RESULTS A N D DISCUSSION
The standard glass samples with known amounts of lead gave straight
U. S. Customs Laboratory 103 South Gay Street Baltimore, Md. 21202
A Rapid Determination of Individual Mercaptans in Gasoline Boiling Range Stocks SIR: Mercaptans impart an undesirable odor to petroleum products and differ in susceptibility to treatment, partly because of the differences in the ease with M hich different mercaptans respond to conversion or removal. It is therefore important to know not only the total mercaptan content of a sour stock, but the concentration of the different mercaptans present. Many gas liquid chromatographic procedures are available which are capable of separating simple mercaptan mixtures for qualitative identification ( I , 3-5, 12, f4,f5). For quantitative analysis, to avoid the multiplicity of peaks and distinguish mercaptans from other components in sour gasoline, two general approaches have been used. I n the first the sour stock may be chemically treated to concentrate the mercaptans and separate them from most other components. + i n extraction using alcoholic sodium carbonate has been proposed by Liberti and Cartoni (8),but this extraction is only semiquantitative (2, 11) for pentyl and higher mercaptans (
