Sentence:  The instruments in which the oxigen gas of a determined quantity of air was ascertained, received the name of EUDIOMETERS, because they were considered as measurers of the purity of air. They are however more properly called <WSD>OXIMETERS</WSD>. 
Meaning of the word marked with <WSD> tags:  A device that measures the quantity of oxygen in something, particularly air in the atmosphere.