Sentence:  Liter quantities of Mallinckrodt , low sulfur , reagent grade carbon tetrachloride were saturated with * * f and * * f and illuminated for about 50 hours with a 1000 watt tungsten lamp at a distance of a few <WSD>inches</WSD> . 
Meaning of the word marked with <WSD> tags:  a unit of length equal to one twelfth of a foot