fork 15 extends in operation if the vibrating tuning fork is free of material the system begins to vibrate at its resonant frequency and within a predetermined time frame an internal relay is energized in the system of the present invention the internal relay is connected with vacuum source 6 via electrical conduit 16 such that when air is present between the prongs of the tuning fork 15 vacuum source 6 is activated and microbubbles are delivered from storage container 2 to holding vessel 8 via vacuum delivery conduit 4 once the prongs of the tuning fork 15 become covered with microbubbles the change in frequency of oscillation causes the internal relay to be deenergized after a predetermined interval of the time in the present system deenergizing the relay causes vacuum source 6 to cease delivery of microbubbles to holding vessel 8 the electric signal being communicated to vacuum source 6 along electrical conduit 16 a suitable tuning fork level indicating mechanism is manufactured by endress amp hauser inc greenwood ind and is sold under the trade name vibratrol thus by employing the above type of level indication system in combination with a vacuum source or other delivery systems the delivery of microbubbles to.