Unpublished diagram, 'gas-holder' by George Stillingfleet Johnson A diagram in black ink showing the equipment used by Johnson in his experiments on allotropic or active nitrogen and on the complete synthesis of ammonia, consisting of a glass cylinder, 'tapering at its two extremities, into which [are] attached corks.' The upper cork is connected to a delivery tube, while the lower cork is connected to a U-shaped tube, which connects at its other end to a water reservoir. Subject: Scientific apparatus and equipment 1881