A radiochemical technique has been combined with a modification of the surface combustion method of Schöberl to give a rapid method for the determination of sulphur in the range 1 to 10 p.p.m. in organic substances such as purified light petroleum. The sulphate formed is precipitated with barium chloride labelled with barium-133, and the amount of barium sulphate obtained determined by measuring its activity. A radiometric finish has the advantage of potential sensitivity, and barium-133 can be obtained with a specific activity of 1 Ci per g. Thus, a scintillation counter with an efficiency of 30 per cent. and a background of 20 counts per second (shielded) can detect 0·4 × 10^–3µg of sulphur, as barium sulphate, assuming no solubility losses.

The lowest detectable concentration of sulphur is dependent on the magnitude of the blank value, but because sulphate appears to be an almost universal contaminant it was found, under normal laboratory conditions, that it was impossible to reduce the blank value to much below the equivalent of 1 p.p.m. in the sample.