This simple Charles’ law tube consists of an unmounted, uniform capillary tube, which is sealed at one end and has a linear scale along its length, marked in cm and mm. Although traditionally used with a bead of mercury, a bead of concentrated sulphuric acid or coloured oil can be used instead, by inserting about half way down the tube, which can then be heated in a water bath to investigate temperature/volume for the enclosed air column. To place a bead of liquid into the capillary it is best to ensure the tube is thoroughly dried in an oven first, at high temperature for an hour or two. After removing from the heat, if the tube is then immediately placed with the open end in some coloured oil or sulphuric acid, a bead of liquid should be drawn into the tube as it cools down. Readings are taken directly from the scale on the tube. Comes supplied in a protective plastic case, with instructions.