A version of the hydrogen clock, also known as the gas-operated clock, is in the Clockmakers' Company Museum in London; it was designed by Pasquale Andervalt in Italy c. 1835. It consists of an open-centered dial exposing the mechanism, with a pin-pallet escapement and ornate gilt pendulum bob, the clock movement being mounted on supports fixed to a large red glass cylinder. Above the movement is a coiled spiral brass tube holding balls of zinc which, as the driving weight nears its lower position, are released one by one to fall into a solution of dilute sulphuric acid in the red glass jar. Hydrogen gas is generated and the resulting pressure lifts the entire mechanism behind the dial, winding the going weight, the larger of the two visible. The smaller weight is used to maintain the clock in motion whilst the larger is wound, the winding process being quite slow. On completion of the winding the hydrogen gas is released in preparation for the next cycle. These clocks are rare; hydrogen is a most inflammable gas and perhaps the majority have exploded in use.