1 A BURETTE Technical Field The present invention relates to burettes and more particularly but not exclusively to medical burettes used to administer intravenous liquids. 5 Background of the Invention Australian Patent No. 689324 (equivalent to USA Patent No. 5885532) describes a medical burette that controls the flow from an intravenous liquid supply to the patient, while providing for the delivery of secondary liquids via a septum or the like. The above device is complex in its structure and therefore is relatively expensive io to manufacture. A further disadvantage of the above discussed burette occurs when the burette is to be used to dispense a medication. In such a use, delivery of liquid from an IV bag is terminated. Liquid is still delivered from the burette until the outlet is closed. However when the outlet is closed there is still considerable residue liquid in the burette. The is medication is then added with the effect that the medication is substantially diluted by the residue liquid. When the medication has been delivered and again the outlet closed by the drop in fluid in the burette, a significant portion of the medication is still retained in the burette. Accordingly not only is the medication diluted, but the full medication is not delivered. 20 Object of the Invention It is the object of the present invention to overcome or substantially ameliorate the above disadvantage. Summary of the Invention There is disclosed herein a burette comprising: 25 an elongated hollow body having a longitudinal axis that is to be generally vertically oriented during use, the body including a chamber to receive a liquid to be dispensed by the burette; an inlet passage extending inwardly of the chamber so as to terminate with an end extremity in the chamber via which liquid is delivered to the chamber; 30 an outlet extending from the chamber, the outlet being located below the inlet extremity; and a float valve located between the inlet passage and outlet and movable 2 therebetween in response to changing liquid levels in the chamber, the float valve including a hollow floatation body enclosing a chamber, the hollow floatation body including a top wall having a recess to hold liquid, the recess being vertically aligned with said extremity so that when liquid level in said chamber is above a 5 predetermined level said extremity is located below liquid level in said recess to at least inhibit flow to said chamber through said passage, with the liquid level in said chamber falling below a predetermined level causing said float valve to engage said outlet to close said outlet to prevent further liquid from leaving said chamber. Preferably, said inlet passage is provided by a tube. 10 Preferably, said chamber is vertically elongated with said inlet further including a hollow stem having a lower end within which said tube is mounted, with said stem having an upper end to which a supply of the liquid is to be attached. Preferably, a guide within which said float valve is located so as to be guided thereby for generally vertical movement between an upper position at which said is extremity is located in said recess, and a lower extremity closing said outlet. Preferably, the guide provides a socket within which the float valve is located when closing the outlet. There is further disclosed herein a burette comprising: an elongated hollow body having a longitudinal axis that is to be generally 20 vertically oriented during use, the body including a chamber to receive a liquid to be dispensed by the burette; an inlet passage extending inwardly of the chamber so as to terminate with an end extremity in the chamber via which liquid is delivered to the chamber; an outlet extending from the chamber, the outlet being located below the inlet 25 extremity; and a float valve located between the inner passage and the outlet and movable therebetween in response to change in liquid levels in the chamber, the float valve having a hollow body including a float chamber with an upper portion, the body providing floatation, a first closure member mounted in the hollow body to 30 engage the end extremity to close said passage, and a second closure member mounted in the hollow body to engage the outlet to close the outlet, so that upon the liquid level in the chamber being above a predetermined level said first closure member closes said end extremity, while when liquid level in the chamber falls below a further predetermined level, said second closure member closes said outlet, and 35 wherein the hollow body has a top wall, closing said upper portion of said 3 chamber, and at which the first closure member is located, and said first closure member and said second closure member are resilient pads. Preferably, said first and second closure members are aligned along said axis. Preferably, said second closure member directly engages said outlet. 5 Preferably, said second closure member provides a seal surrounding said outlet to thereby isolate said outlet from said chamber so that said outlet is effectively closed. Brief Description of the Drawing A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings wherein: 10 Figure 1 is a schematic side elevation of a burette and an associated bag to provide a liquid, such as a saline solution; Figure 2 is a schematic sectioned side elevation of the burette of Figure 1; Figure 3 is a schematic sectioned side elevation of a modification of the burette of Figure 2; is Figure 4 is a schematic exploded sectioned side elevation of portion of the burette of Figure 3; Figure 5 is a schematic sectioned isometric view of a modification of the burette of Figure 2; and Figure 6 is a schematic sectioned side elevation of the modified burette of Figure 20 5. Detailed Description of the Preferred Embodiment In Figures 1 and 2 of the accompany drawings there is schematically depicted a burette 10. The burette 10 is a medical burette and is intended to receive liquid from an intravenous liquid supply (bag) 29, to deliver the liquid to a patient via a tube 30.
WO 2007/041787 PCT/AU2006/001495 The burette 10 includes a hollow body 11 that is generally cylindrical and surrounds a chamber 12. Preferably the body 11 is transparent so that a user may observe the liquid level in the chamber 12. The upper end of the body 11 is closed by means of a top wall 13 having ports 5 14 via which another liquid may be delivered to the chamber 12. Mounted in the wall 13 is an inlet assembly 16 including an elongated hollow stem 15 terminating at its upper end with an extremity 17 with which there is engaged a flexible tube 18 extending to a supply of intravenous liquids, such as a flexible bag. The assembly 16 further includes a tube 19 having a longitudinal passage 36. 10 The tube 19 extends inwardly of the closed lower end of the stem 15 and projects outwardly from the stem 15 so as to have a lower extremity 20 of the passage 36 located in the chamber 12. In use liquid enters the stem 15 and ultimately flows through the tube 19 (passage 36) exiting via the extremity 20 to be delivered to the chamber 12. The lower end of the body 11 is closed by means of a plug 21. Mounted in the 15 plug 21 is an outlet tube 22 having an upper extremity 23. Located between the extremities 20 and 23 so as to be generally vertically aligned with the tubes 19 and 22 is a valve float 24. The float 24 has a recess 25 that receives liquid that is located in the chamber 12. The plug 21 has a recess 26 having side walls 27 that guide the valve float 24 in 20 its movement that results from changing liquid levels in the chamber 12. The recess 26 acts as a socket to receive the float 24 to thereby minimise the residue liquid when the outlet tube 22 is closed. The tube 22 delivers liquid to an outlet 28. In operation of the above described medical burette 10, when liquid is delivered 25 to the chamber 12 the float 24 rises until liquid in the recess 25 engages the extremity 20 to thereby prevent further flow through the tube 19. When liquid level in the chamber 12 falls below a predetermined level the float valve 24 engages the extremity 23 to close the outlet tube 24. The float valve 24 is guided in its vertical movement by means of walls 27 and is caused to move between its upper and lower positions by changing liquid levels in 30 the chamber 12, so as to provide a regularly constant flow to the tube 22, that is the outlet 28. -4- WO 2007/041787 PCT/AU2006/001495 Preferably the burette 10 is adapted to be suspended so as to have a longitudinal axis 29 that is generally vertically oriented. The burette 10 is attached to the bag 29 by tubes 31 and 32 that are arranged in parallel and are connected to the bag outlet by means of a tube 33. The tube 32 is 5 attached to one of the ports 14 to aid in the initial charging of the burette 10. Preferably the tube 32 would have associated with it a clamp 34 that could be operated to close the tube 32. An adjustable clamp 35 is also applied to the tube 31 to aid in regulating the flow therethrough. In Figure 3 there is schematically depicted a modification of the burette 10 of 10 Figures 1 and 2. In this embodiment the stem 15 is maintained in position at its lower end by a plurality of fins 37 that extend radially from the lower end of the stem 15 to gauge the internal surfaces of the body 11. The valve float 24 has a frusto-conical longitudinal wall 38 that converges upwardly toward the axis 29, with the wall 38 joining a top wall 39 and a bottom wall 40. 15 The top wall 40 includes a recess providing member 41 having a hollow projection 42 providing the recess 25. The projection 42 has an upper opening 43 through which the tube 19 passes to enter the recess 25 so that the lower extremity 20 of the passage 36 can be located in the recess 25. The lower portion of the recess 25 is provided with a resilient pad 44 that is engagable with the lower extremity 20 to aid in closing the lower extremity 20 20 by engagement therewith. The bottom wall 40 has attached to it a hollow projection 45 that receives the tube 22. More particularly the projection 45 has an opening 46 through which the tube 22 projects to have its upper extremity 23 engagable by a resilient pad 47 held in position by the projection 45. When engaged by the pad 47, the extremity 23 is closed. 25 In the embodiment of Figures 4 and 5, the stem 15 is provided at its lower end with a passage 50 having a lower extremity 51 closed by the float valve 52. The float valve 52 has a hollow body 53 of generally annular configuration providing a generally longitudinal central passage 54. Located in the passage 54 is a resilient valve member 55 having an upper extremity 56 (providing a first closure member) that is engaged with the 30 lower extremity 51 of the passage 50 to close the passage 50. The lower portion of the resilient valve member 54 has an annular sealing portion 57 (second closure member) that engages the bottom wall 58 through which the tube 22 projects so that the upper extremity -5- WO 2007/041787 PCT/AU2006/001495 is sealingly surrounded by the portion 57 so as to be closed thereby. The valve float 52 moves between the passage 50 and tube 22 in accordance with liquid level within the chamber 12. When at its upper limit the lower extremity 51 is closed, while at its lowest most extremity the tube 52 is closed by being isolated from the chamber 12. Accordingly s the position of the valve float 52 regulates liquid level within the chamber 12. In the embodiment of Figure 6, the lower end of the stem 15 is supported by fins 58 extending to a rim 59 that engages the body 11. The valve float 52 has resilient pads 60 and 61 (first and second closure members), with the pads 60 being provided to close the passage 50 and the pad 61 provided to close the tube 22. 10 The pads 60 and 61 are located on the longitudinal axis 29, together with the extremity 50 and tube 22. -6-