Sentence:  Surface temperature gradients have been found to exist in liquid helium baths contained in 15 - and 25 - <WSD>liter</WSD> metallic storage dewars . 
Meaning of the word marked with <WSD> tags:  a metric unit of capacity, formerly defined as the volume of one kilogram of pure water under standard conditions; now equal to 1,000 cubic centimeters (or approximately 1.75 pints)