An Automatic Drop Recorder.

Abstract

This drop recorder was designed to meet the requirements of perfusion and excretion experiments where a continuous record of outflow is desired. It differs in principle from the mechanical type of drop recorder in that the conductivity of the solution itself is employed to close the electrical circuit, thus avoiding completely the uncertain response produced by impact of the falling drops with a weighted or spring lever. It operates with solutions containing electrolytes even in low concentrations, f. i., with Cleveland tap water, but it is not suitable for use with distilled water.

Fig. 1 illustrates the electrical circuit. The drops, as they pass the tips of 2 contact points, close a primary circuit which works a 100 ohm “pony” relay (f. i., Cat. No. 573, J. H. Bunnel and Co., New York). A signal magnet is activated through the relay by 2 dry cells.

The relay is best operated by a direct current of 110 volts; but alternating current may be used if the height from which the drops fall is so adjusted that the latter make contact at the points for a time which is less than a half-cycle of the current (usually 1/120th second). A fall of 3 to 4 cm. will be found satisfactory if the points are properly adjusted. The 10 watt lamp is placed in the primary circuit to protect the relay in case the points should accidentally become short-circuited. If the solution used contains electrolytes equivalent to 0.9% NaCl or over, a 221/2-volt current (from a radio “B” battery) may be used instead of the 110-volt current (in which case the lamp may be omitted) but the use of 110 volts as standard affords an apparatus of wide adaptability.