Sentence:  The gradient was about one half of a millidegree at 4.2 * * f but increased to several millidegrees for <WSD>bath</WSD> temperatures slightly greater than the | l point . 
Meaning of the word marked with <WSD> tags:  a vessel containing liquid in which something is immersed (as to process it or to maintain it at a constant temperature or to lubricate it)