1. Shake test tube Since the start of precipitation The mixture is then concentrated. But in experiments with a mixture of experiments conducted into the tube itself. The first is a solid mix of sinking to the bottom of the tube anyway. If the experiments do not shake it thoroughly to make a residual sludge at the bottom of the tube before starting the timer in the trial. To make the substance in the tube with the height of the seam of the concentrate to the clear error in any period. As a result, the speed of sinking errors of fact. If the mixture is concentrated initially uneven. It will cause errors in the sinking of the solid particles. In experiments conducted by the shaking test tubes without observing that the mixture has a concentration regularly or not. It mixture is concentrated uneven. Solid particles fall to the bottom of the tube, at first making a mixture of solid particles less than it should be. So that the solid particles settle faster than it should be.