Article

AN IMPROVED DROPPING APPARATUS FOR PREPARING THE ANTIGEN SUSPENSIONS FOR THE SIGMA TEST

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Abstract

IN the official description of the Sigma test (Dreyer et. al., 1923) an all-glass floating syphon is shown, and a modified arrangement is given by Fildes (1931) which uses the tip of a Dreyer's pipette as part of the syphon fitted to a constant-level apparatus. In each case certain disadvantages are experienced. The all-glass syphon was difficult to balance correctly while floating, and to adjust so that it delivers drops at the correct rate. In addition it is an elaborate piece of glass-blowing and therefore expensive. With the modified arrangement referred to by Fildes a very large volume of saline solution is required, and the tip of the syphon can be used only for this one purpose. Also, the very decided oscillatory disturbance of the surface level in the bottle every time the air bubbles into the flask causes a variation in the rate of dropping. The method for adjusting this rate by slipping the rubber con-necting piece up or down the stem is not a very delicate one, and involves some risk of breaking the syphon. To surmount these objections, and give extra accuracy and reliability, I have designed an arrangement of apparatus which consists of-(1) An iron retort stand, about 24 in. high, fitted with a ring and a clamp. (2) A 500 c.c. flat-bottomed flask, fitted with an india-rubber stopper, and a bevelled outlet tube (about 3/8 in. diameter). (3) A 4 in. U-tube, about 5/8 in. diameter. (4) A Dreyer's pipette, held with a clip on the outer limb of the U-tube. (5) A connecting capillary bridge, 2 mm. diameter, with limbs about 3*5 in. long and 1 in. apart. The sketch shows the well-known arrangement of apparatus for maintaining a constant level in any vessel, such as the U-tube in this case, and the improve-ment in the design consists in the use of the complete Dreyer's pipette, which is supported by the U-tube and fed by means of a capillary bridge syphon with saline solution from the ()-tube. The clip for holding the pipette can easily be made of springy hoop iron or brass strip about 1/2 in. wide. It is fitted round the U-tube, and at about 1 in. distance the limbs are bent to embrace the pipette. The grip is obtained by using a small bolt and nut fitted between the two tubes, and tightening it to give a smooth sliding fit, especially on the pipette.

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