US 3252331 A
Description (OCR text may contain errors)
May 1966 J. F. LANCASTER 3,252,331
LABORATORY APPARATUS Filed Nov. 25, 1964 INVENTOR JESSE E LANCASTER BY k M ATTOR N KY6 United States Patent 3,252,331 LABORATORY APPARATUS Jesse F. Lancaster, Great Falls, Va., assignor to Cooke Engineering Company, Alexandria, Va., a corporation of Delaware Filed Nov. 23, 1964, Ser. No. 410,421 17 Claims. (Cl. 73-425.4)
This invention relates to laboratory apparatus and, more specifically, to improvements in liquid transfer devices or dilution loops which may be advantageously used with microtitration apparatus of the type disclosed in copending application SerialNo. 135,364 filed August 31, 1961, by Alan A. Duff et al.
Typical examples of prior art liquid transfer devices suitable for use in microtitration are illustrated in the aforesaid copending-application, in copending application Serial No. 189,491 filed April 23, 1962 for Laboratory Apparatus by Alan A. Duff and in United States Patent No. 3,077,780 issued February 19, 1963, to G. Takatsy for Volumetric Liquid-Transfer Device. While as these applications and patents indicate, various liquid transfer device configurations have been heretofore proposed, in actual commercial practice, so far as I am aware, only liquid transfer devices formed of wound wire loops have been used. Such wire wound loops have the disadvantage in that they are very diflicult if not impossible to wind with a precise volumetric capacity so that each loop must be individually inspected and calibrated, if not within specified tolerances, before it is delivered to the customer for use. In addition, such wire wound loops are relatively fragile in that their configuration can be permanently deformed if they are dropped or even if roughly laid on a worktable so that it is necessary to frequently check the calibration of the loops and discard or recalibrate the loops which are not in calibration. The delicate construction of these loops thus results in increased time and expense in manufacture, loss of time in use and relatively short life. The heretofore proposed alternatives to wire loops have not found acceptance commercially for various reasons. Those formed of sheet metal are expensive to manufacture and assemble, require individual calibration in manufacture, are difiicult to clean and sterilize, and still are subject to deformation in use, destroying the calibration. Others while of relatively rugged construction are not susceptible of calibration at all so that, if very precise volumetric capacities are required, must be manufactered to exactly perfect dimensions and therefore are impractical from the manufacturing viewpoint. Certain others of the heretofore proposed designs are impractical in that they will not rapidly take up liquid by capillary attraction or fully discharge the entire content of the liquid transfer device when required. Since the liquid volumes involved are so very small in microtitration techniques, the retention of any liquid at all by the liquid transfer de vice can completely destroy the accuracy of the results of any microtitration procedures.
With the foregoing general considerations of the prior art in view, the principal objects of the present invention are to provide a liquid transfer device or dilution loop which:
(a) Is susceptible of manufacture by conventional manufacturing techniques with sufficient accuracy so that its volumetric capacity can be established within the required tolerances without individual calibration of each such device;
(b) Is of one-piece construction;
(c) Has sufficient rigidity that it will not be deformed in normal usage;
(d) Will rapidly pickup and fully discharge the precise volume of liquid for which it is designed;
(e) Is designed to give thorough agitation of the liquid within a receptacle upon rotary oscillation therein to thereby assure thorough and uniform mixture of the liquid within such a receptacle and the liquid within the liquid transfer device;
(f) Which is highly corrosion resistant;
g) Which has excellent resistance to scaling at high temperatures permitting flame sterilization; and
(th) Which has an etched surface within its internal passage and its exterior surfaces to improve the pickup and discharge characteristics of the device.
These and other objects of the present invention will become more fully apparent by reference to the appended claims and as the following detailed description proceeds in reference to the accompanying scale drawings wherein:
FIGURE 1 is a full size drawing of a liquid transfer device constructed in accord with the present invention and constituting the preferred embodiment thereof;
FIGURE 2 is an enlarged view of the lower end of the device of FIGURE 1;
FIGURE 3 is a bottom view of the structure of FIG- URE 2;
FIGURE 4 is a full scale view of a liquid transfer de vice in accord with the present invention showing an alternative construction;
FIGURE 5 is an enlarged view of the lower end of the A liquid transfer device of FIGURE 4;
FIGURE 6 is a bottom view of the structure of FIG- URE 5;
FIGURE 7 is an enlarged view of the lower end of a further form of liquid transfer device constructed in accord with the present invention; and
FIGURE 8 is a sectional view taken substantially along the line 8--8 of FIGURE 7.
Referring now in detail to the drawings and particularly to FIGURES l, 2 and 3, wherein the preferred embodiment of the present invention is illustrated, the liquid transfer device 10 comprises an elongated handle 12 and a one-piece head 14 consisting 'of an elongated shank 16 and a liquid entrapping cage 18. As is apparent from FIGURE 2, the upper end of the shank 16 extends within an aperture 20 formed coaxially in the lower end of the handle 12. The upper end of shank 16 is fixed within the aperture 20 either by a forced fit or by any other suitable means establishing a substantially permanent connection between the head 14 and the handle 12.
The head 14 is of one-piece construction being formed from cylindrical stock on a screw machine or other suitable conventional machining equipment. The shank 16 is preferably cylindrical. In its preferred form, the liquid entrapping cage has an external cylindrical wall 22, a frustoconical wall 24 extending between the upper end of the wall 22 and the shank 16, a frustoconical surface 26 providing a slight bevel at the lower end of the cylindrical wall 22, and a planar bottom surface 28. The surfaces 22, 24, 26 and the shank 16 are preferably all coaxial and coaxial with the axis of the handle 12.
The liquid entrapping cage has a central chamber 30 x which is opened through the bottom surface 28 and a plurality of radiating passages 32 extending from the chamber 30 preferably radially outwardly through the surfaces 22 and 26. In the illustrated embodiment there are eight passages 32. The passages 32 and the central chamber 30 are formed by making four diametral cuts through the liquid entrapping cage material 18, the volumetric capacity of the cage 18 being determined by the width of the cuts and the depth of the cuts from the surface 28. Since the external dimension of the head 14, the thicknesses of the cuts which provide passages 32 and the depth of the cuts which provide those passages can be very precisely controlled, the resultant volumetric capacity of the liquid entrapping cage 18 can be accurately predetermined so that, so long as the parts are made to specified tolerances,
It has been found for example, that, for a liquid transfer device constructed as shown in FIGURES 1, 2 and 3 to have a volumetric capacity of .025 milliliters, the diameter of the surface 28 may be .120 inch-003 inch, the diameter of the surface 22 .155 inch plus .002 inch minus .000 inch, the cha'mfer provided by the surface 26, 45 degrees, the width of the passages 32 .016 inch plus .002 inch minus .000 inch, the axial length of the surface 22 .170 inch-1:005 inch and the depths of. the passages 32 axially of the liquid entrapping cage 18 .158 inch plus .002 inch minus .000 inch. These tolerances can be readily maintained by careful conventional machining practice and when maintained provide the necessary accuracy in volumetric capacity of the liquid entrapping cage 18. In the preferred form, the head 14 is formed of type 321 stainless steel. This material is designed for high temperature chemical handling equipment. It has a high titanium content for extra corrosion resistance and has excellent resistance'to scaling at high temperatures. After the head 14 has been machined, it is passivated to remove all foreign particles on its surfaces due to tool erosion during the machining process. It is then annealed to eliminate magnetism caused by cold working of the material. The head is then etched in a solution of one part nitric acid and three parts hydrochloric acid for a period of time sufficient to produce a satin finish. A satin finish formed in this manner has been found to improve the pickup characteristics of the liquid entrapping cage so that only slight immersion of the lower end of the liquid entrapping cage 18 in the liquid is required for the chamber 30 and the passages 32 to become completely filled with the liquid by capillary attraction. Finally, the exterior surfaces of the liquid entrapping cage 18 are electroplated with a very thin coating of gold, known as gold flash. This coating is primarily to improve the appearance of the unit without producing any deleterious effect upon its liquid pickup and discharge characteristics or its ability to withstand substantially indefinitely the effect of corrosive fluids and high temperatures as required for sterilization and use.
In the rare instance when more precise volumetric calibration is required than that that is achieved by construction as described above, the liquid entrapping cage 18 can be calibrated by slight bending of the portions of the liquid entrapping cage 18 lying between one or more adjacent pairs of passages 32 radially inwardly toward the chamber 30 or radially outwardly.
As is known, in the use of liquid transfer devices of the type to which the present invention relates, a plate is providedwhich has a row of liquid receptacles or cups in which is deposited equal volumes of a first liquid, the liquid transfer device is filled with a second liquid, and then successively immersed and rotated within the liquid in each cup in the row to thereby form progressive dilutions of the second liquid. The construction of the present invention facilitates this action in that as the liquid transfer device is rotated within the liquid in a given cup, the liquid entrapping cage 18 functions as a centrifugal impeller or pump having an axial inlet at the bottom through the surface 28 directly into the chamber 30 and radial outlets through the passages 32. This assures rapid and effective circulation of the liquid within the receptacle in which the liquid transfer device is being rotated to effect complete intermixture between the liquids which were in the cup and in the liquid entrapping cage 18 prior to the immersion of the latter into the former. It-will be noted that the upper end of the chamber 30 is co-planar with the upper ends of the passages 32 so that there are no pockets wiithin the passages 32 or the chamber 30 in which liquid is retained or trapped. This assures that all of the liquid within the liquid entrapping cage 18 is thoroughly mixed with the diluent.
The embodiment illustrated in FIGURES 4, 5 and 6 is in all respects identical with the embodiment described above in reference to FIGURES 1, 2 and 3 except that a hemispherical or conoidal surface 34 is provided at the lower end of the liquid entrap-ping cage 36 in lieu of the bevel 26 and the planar surface 23. This hemispherical or conoidal surface 34 is preferable for certain applications such as where the bottom or end wall of the cup or receptacles of the microtitration plates is of hemispherical or conoidal form in that it permits the bottom end of the liquid entrapping cage to touch the bottom of the cup or receptacle and fully drain the liquid content thereof whereas in certain situations, the flat surface 28 of the liquid entrapping cage 18 may preclude this. The embodiments of FIGURES 1, 2 and 3 is preferred however to that of FIGURES 4, 5 and 6 because this requirement is very infrequently encountered and the design of FIG- UR'ES 1, 2 and 3 is generally more rugged and less susceptible of deformation from calibration by rough handling in use.
FIGURES 7 and 8 illustrate a still further embodiment of the present invention. This embodiment consists of a handle 38 and a head 40. The head 40 is of one-piece construction consisting of a shank 42 and a liquid entrapping cage 44. The cage 44 has a single diametral slot 46 intersectedby a diametrally extending cylindrical through passage 48. While this liquid transfer device functions generally satisfactorily, it is less satisfactory than those of the first two embodiments in that liquid pickup is not as rapid and in that, with certain liquids, difficulty has been found from time to time in assuring complete drainage of the liquid from all of the interior passages.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
What is claimed and desired to be secured by Letters Patent is:
1. A volumetric liquid transfer device comprising a rigid one-piece liquid entrapping cage for carrying a liquid having a surface tension, said cage having an exterior configuration including an axially elongated annular surface portion and end surfaces at opposite ends of said annular surface portion which are symmetrical with the axis of symmetry of said annular surface portion and in which the portion of said cage defined by said annular surface portion and at least one of said end surfaces is provided with a central chamber extending axially from and through said one end surface and a plurality of capillary channels communicating with and radiating from the chamber of said cage, the size of each such capillary channel being not greater than that which will retain said liquid in said cage by surface tension.
2. The device defined in claim 1 wherein said annular surface is cylindrical.
3. The device defined in claim 1 wherein said one end surface is planar and joined with said annular surface by a small conoidal bevel.
4. The device defined in claim 1 wherein said one end surface is conoidal.
5. The device defined in claim 1 wherein said one end surface is conical.
6. The device defined in claim 1 wherein said plurality of channels extend outwardly from said chamber through both said annular and said one end walls.
. 7. The device defined in claim 6 wherein said channels are of uniform width normal to said axis of symmetry.
8. The device defined in claim 6 in which the end walls of said channels-remote from said one end surface are spaced from said one end surface at least as far as the end wall of said chamber.
9. The device defined in claim 6 wherein said channels are equiangularly spaced about said axis of symmetry.
10. The device defined in claim 9 wherein there are at least six of said channels.
11. The device defined in claim 9 wherein the junctures of the portions of said cage intermediate said channels with the remainder of said cage are sufiiciently ductile that said portions can, without breakage, 'be slightly permanently displaced radially inwardly and radially outwardly with respect to said axis of symmetry to vary the cross-section of the channel at each side of such cage portion to thereby permit precise accurate calibration of the volumetric capacity of said chamber and channels.
12. The device defined in claim 1 wherein the material of which said cage is formed is a stainless steel.
13. The device defined in claim 12 wherein said stainless steel has a high titanium content for extreme corrosion resistance and resistance to scaling at high temperatures whereby said cage may be flame sterilized Without deterioration or change in its calibration.
14. The device defined in claim 13 wherein said stainless steel is AISI #321 18-10 Ti.
15. The device defined in claim 1 wherein the liquid contacting surfaces of said cage have a satin finish.
16. The device defined in claim 1 wherein the liquid contacting surfaces of said cage have an etched satin finish.
17. The device defined in claim 1 wherein said cage is coated with a thin gold plate.
No references cited.
LOUIS R. PRINCE, Primary Examiner.