Karl Vierordt collected gases in his expirator and then measured the volume by water displacement. From Genusus, Swiss Journal of the History of Medicine and Sciences, volume 38, 1981, an article titled “Die anfange der spirometrie im 19.Jahrhundert” by Mienem Lehrer, page 248.
Karl von Vierordt used his “expirator” to collect exhaled air and then measured volume by immersing it and seeing the volume change in water.
From http://www.timely-cost.eu/sites/default/files/ppts/tempProcSenses/talks/Wearden.pdf
The diverse, quirky and mostly forgotten history of Pulmonary Function testing