A New Form of Drop Recorder

Abstract

Gibbs 1 classifies the drop recorders reported in the literature according to the essential mechanism as follows: (a) impulse, (b) weight, (c) expansion, (d) electrolytic, and (e) displacement. The simple and effective drop recorder here described depends upon a principle quite different from any described heretofore, and resulted because of our trial and abandonment of some of the most promising types, including that described by Gibbs. 2

The essential part of our form of drop recorder consists of a short length of capillary tubing sealed to a bulb and T tube. A current of air from a pump or compressed air jet flows through the T tube and bulb and out of the capillary tube. The drops to be recorded as they fall from the drop inlet are blown through the capillary tube and momentarily hinder the passage of air sufficiently to create a slight increase of back-pressure that may be used to actuate a tambour or other recording device.

The air pressure required is very slight, equivalent to a few centimeters of water, and requires no careful adjustment or maintenance of a constant pressure. The pressure required for the blowing out of the drops is so low that it is entirely compensated for by a few centimeters head of hydrostatic pressure in the drop inlet tube and ureteral or other cannula or catheter attached to the upper end of the drop inlet. If the size of the drops to be recorded is of importance, a change of the drop inlet tube, which may be a hypodermic needle of any gauge, a drawn-out glass tube, a suitable cannula, or a small metal tube, may be made without trouble. Drops as small as 0.01 cc. or as large as 0.05 cc. have been used with entire success. The degree of viscosity (for example, 15% gum acacia solution) or the character of the fluid (electrolyte content) are also unessential for the satisfactory operation of this form of drop recorder, so long as discrete drops may be obtained.