A CHEAP AND ACCURATE HOME-MADE AUTOMATIC
                                         PIPETTE

                                             BY

                  JOHN B. POLDING, B.Sc., M.R.C.V.S.

    Imperial Veterinary Research Institute, Mukteswar-Kumaun

               (Received for publication on 22 August 1941)

                              (With three text-figures)

IN many bacteriological laboratories, certain routine technique can be
simplified by employing an automatic distribution apparatus. Such
an apparatus is particularly useful in filling antigen when numerous agglutina-
tion tests are to be performed. Instruments may be purchased from manu-
facturers but they are costly and, in the writer's experience, not always satis-
factory. Home-made apparatus is often fragile and requires delicate adjust-
ing and maintenance. The instrument about to be described costs only a
few shillings and can be made by a good machinist in two or three hours.
It is not easily damaged and, once calibrated, remains accurate indefinitely.
In addition, it can be operated by unskilled labour and, by the simplest inter-
change of parts, can be made to deliver any predetermined quantity from 0.25
c.c. to 10 c.c.

The instrument is essentially a pump and consists of two parts—a valve
chamber with valves (Fig. 1) and a cylinder with piston (Fig. 2). This form
of construction is admittedly not new but its appeal lies in its simplicity,
strength and cheapness.

CONSTRUCTION OF VALVE CHAMBER AND VALVES (Figs. 1 and 2)

The valve chamber is made from the barrel of a discarded 5.0 or 10.0
c.c. all metal syringe, as follows :—

(i) The syringe is taken to pieces and a short section of small bore nickle
tube is soldered into the external aperture of the barrel cap (Fig. 1, valve
cap A). This portion will in future be referred to as valve Cap A. (ii) A
section measuring 1½ in. from the open end of the barrel is cut off and the
nozzle end of the barrel is discarded. It will be noticed that one end of this
section is already screw-threaded. The opposite end should now be threaded
in like manner. This section of barrel is referred to as the valve chamber
(Fig. 1). (iii) Two collars to fit the bore of the valve chamber are cut from
⅛ in. brass plate and a ¼ in. hole bored through their centres. They are
soldered, one in each end of the valve chamber, to fit flush with its edges.
(iv) The wall of the valve chamber is pierced in the middle of its length and
the butt of a large record-type needle is soldered into the hole so made.
(v) A cap to screw on the newly threaded end of the valve chamber and
identical in shape with the nozzle cap of the discarded piece of barrel is turned.
(The old nozzle cap of the syringe cannot as a rule be modified for this purpose,
as, having been sweated on the barrel, it is just too large to take a thread
which will screw on to the valve chamber). The inner face of the cap is
fitted with a fibre, or hard rubber washer ⅛ in. in thickness and bored in
the centre with a ¼ in. hole. This cap is referred to as valve cap B (Fig. 1).

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