M&IE backbar, with "Rowlings Balls" in the Boyles bottle
To get an accurate percentage of chloroform, Dr Thompson-Rowling mixed it with inert paraffin. "Rowlings Balls" were spheres of different specific gravities, and which floated and which sank in the mixture would indicate the percentage composition. There was normally just a cork to the bottle, with an inlet tube, and an exit tube to the patient.

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