An improved greenhouse comprising a plurality of walls, a light-transmitting roof panel; and an optical system located inside the greenhouse is described. The optical system comprises a plurality of rows of elongate spaced optical panels generally adjacent and extending transversely across the light-transmitting roof panel. Each panel comprises a thin backing portion forming first and second concave, opposite sides, a first light reflecting means including light-reflecting surfaces attached to the first side of the backing and a second light reflecting means including light-reflecting surfaces attached to the second side of the backing such that the light-reflecting surfaces face generally oppositely. Also disclosed is an improved method of growing plants utilizing such a greenhouse construction.

Precise information about the position of a liquid-liquid interface (28, 32) is often important for the control and automation of molten metal refining processes. For example, in an electrolytic process for removing magnesium from molten aluminum, knowledge of the vertical position of an interface (32) between the electrolyte and the magnesium and an interface (28) between the electrolyte and the aluminum facilitates the automatic removal of the purified metals. Differences in surface tension in the fluid layers of a molten electrolytic salt (30) and a molten metal (29) produce different pressures as bubbles (57) evolved from vertically displaced tips (52) of tubes (34, 36) press against the liquid layers on either side of their interfaces (28, 32). These different pressures are detected by a differential pressure transducer (42) to limit the amount of purified molten aluminum from molten aluminum-magnesium scrap, when drawn through a port (26) in a reaction furnace (10) without risk of also contaminating the purified aluminum with the electrolyte (30) above the interface.

In accordance with the present invention, a method and system is described for controlling the delivery of vapor from a bubbler containing a supply of chemical fluid through which a carrier gas is bubbled and from which bubbler vapors are delivered in a vapor stream entrained with the carrier gas. In general, the present invention involves equilibrating the pressure within the head space to that of the chemical fluid fill line, thus maintaining a constant fluid level based on pressure and not relying on conventional level sensors and controllers.

A method for controlling the delivery of vapor from a bubbler containing a supply of chemical fluid through which a carrier gas is bubbled and from which bubbler vapors are delivered in a vapor stream entrained with the carrier gas. In general, the method involves equilibrating the pressure within the head space to that of the chemical fluid fill line to maintain a constant fluid level based on pressure and not relying on conventional level sensors and controllers.

A bubbler is positioned within a solvent reservoir of a chromatographic system with its opening near the bottom of the system to measure the pressure of solvent. The bubbler may use air or may use helium or some other gas so that the solvent can be purged of excess air while its level is being monitored by the bubbler. The bubbler provides a depth signal to a microcontroller that records the drop in pressure and projects a low level of pressure at which point solvent should be replenished. The microprocessor may provide a signal to the operator or terminate operation or automatically replenish solvent depending upon the program.