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 <WSD>1000</WSD> watt tungsten lamp at a distance of a few inches . 
Meaning of the word marked with <WSD> tags:  denoting a quantity consisting of 1,000 items or units