A delivery system which is operative to deliver a substantially constant number of moles of a vapor of the solid precursor per unit volume of a carrier gas to a plurality of reactors that are in communication with the delivery system, characterized in that said delivery system comprises: a first stream comprising: a delivery device having an inlet port and an outlet port; where the delivery device contains a solid precursor; and a first proportional valve; wherein the delivery device is in operative communication with the first proportional valve; wherein the first proportional valve is operative to control the flow of a carrier gas based on an applied voltage; where the first proportional valve is disposed downstream of the delivery device; a second stream comprising a second proportional valve; the second stream bypassing the delivery device and contacting the first stream at a point downstream of the delivery device to form a third stream; where the third stream comprises: a chemical sensor; the chemical sensor being disposed downstream of the delivery device and being operative to analyze chemical contents of the third stream; the chemical sensor being in communication with the first proportional valve; a first pressure/flow controller being in operative communication with the chemical sensor and with the first proportional valve; a second pressure/flow controller being in electrical communication with the second proportional valve; and a pressure sensor that is in fluid communication with the delivery device; where the pressure sensor is operative to control the flow of the second stream. a first stream comprising: a delivery device having an inlet port and an outlet port; where the delivery device contains a solid precursor; and a first proportional valve; wherein the delivery device is in operative communication with the first proportional valve; wherein the first proportional valve is operative to control the flow of a carrier gas based on an applied voltage; where the first proportional valve is disposed downstream of the delivery device; a delivery device having an inlet port and an outlet port; where the delivery device contains a solid precursor; and a first proportional valve; wherein the delivery device is in operative communication with the first proportional valve; wherein the first proportional valve is operative to control the flow of a carrier gas based on an applied voltage; where the first proportional valve is disposed downstream of the delivery device; a second stream comprising a second proportional valve; the second stream bypassing the delivery device and contacting the first stream at a point downstream of the delivery device to form a third stream; where the third stream comprises: a chemical sensor; the chemical sensor being disposed downstream of the delivery device and being operative to analyze chemical contents of the third stream; the chemical sensor being in communication with the first proportional valve; a first pressure/flow controller being in operative communication with the chemical sensor and with the first proportional valve; a second pressure/flow controller being in electrical communication with the second proportional valve; and a chemical sensor; the chemical sensor being disposed downstream of the delivery device and being operative to analyze chemical contents of the third stream; the chemical sensor being in communication with the first proportional valve; a first pressure/flow controller being in operative communication with the chemical sensor and with the first proportional valve; a second pressure/flow controller being in electrical communication with the second proportional valve; and