A DISPENSING BURET FOR STRONG ALKALI
For the measurement of 50% NaOH for Kjeldahl nitrogen determinations, and in other cases where strongly alkaline solutions are to be measured with a limited degree of accuracy, the apparatus pictured in the accompanyingfigure will be found useful. It can be made from materials to be found around almost any laboratory, and requires only alimited amount of glassworking. The main features of the device are readily seen from the sketch. A is a lipless test tube ll/a''X 8",and it is closed by the three-hole stopper B. One opening of this stopper carries the inlet tube C, coming from the supply bottle which must be at a level above the upper end of the tuhe A. The flow of the liquid from the supply bottle is controlled by a pinch-cock G, placed a t any convenient point in the supply line. The second opening in B carries the delivery tube D, made up of a glass section, a . ,! section of ,rubher tubing, and a glass nozzle, the outflew k i n g controlled by a second pinch-cock I. The third opening carries the safety tube E, leading from a point above the highest desired level in tube A$o above the level of liquid in the supply bottle. In case of leakage through G, or of leaving G open accidentally, the liquid then simply fills the tuhe A, overilows into the safety tube E, rises to the level in the supply bottle and stops. In this way accidental loss of the stock supply is prevented. Determination of the volume delivered may be accomplished by the "cut and try" method, delivering portions into a graduated cylinder until the proper level for the desired volume is found. If more accuracy is desired, thehlet tube may be filled with water and closed by pinch-cock G, any water in the tube A then being drained out. A pipet of the desired capacity is filled to the mark, its tip inserted in the inlet tubing and allowed to drain after opening pinch-cock G. The height to which the liquid rises may then he marked by gummed labels, etc., as a t F. Copper wire binding of the rubber glass junctions a t Wand W' is essential to prevent the creeping out of the alkali a t these points. To use the device after it is assembled it is supported at any convenient height by a condenser clamp and ringstand, and connected to the supply bottle by a sufficient length of rubber tubing attached to the inlet tube C.
Only the lower portions of the supply lime and safety tube are shown in the sketch. For the 50% NaOH and similar viscous solutions care should be taken not to use less than tubing, or the rate of flow will be slow.
