CHEMICAL APPARATUS. 



Dropping Tube, or Pipette. (Fig. 500.) The Fi s- 

 dropping tube, or separating funnel, is a tube of 

 glass, drawn to a point at one end, and furnished 

 with a bulb in some part of its length, both ends 

 being open. To use it, immerse the finer end in 

 the liquid to be taken up, and thrust it down ; the 

 liquid will rise until it finds its level withinside ; 

 then closing the upper end with the finger, it may 

 be conveyed away. The partial or total removal 

 of the finger occasions the fluid to drop from the 

 lower end. Closing it again with the finger stops 

 the flowing ; and thus, if there are two liquids in 

 the tube, such as oil and water, the one may be separated 

 from the other. Price, $0.38. 



Fig. 501. 



Tube of Safety. (Fig. 501.) A tube open 

 at both ends, inserted into a receiver, the 

 upper end communicating with the external 

 air ; the lower being immersed in water. Its 

 intention is to prevent injury from too sudden 

 condensation or rarefaction taking place during 

 an operation. For if a vacuum be produced 

 within the vessel, the external air will enter 

 through the tube, and if the air be generated, 

 the water will yield to the pressure from the 

 confined gas or gases. It is now more fre- 

 quently used of a curved form, like that repre- 

 sented in the cut, with or without a bulb in the 

 upright stem ; the lower end of this, instead 

 of being immersed under the liquid in the 

 receiver as the straight tube, is merely inserted 

 into the tube. The requisite tightness and 

 pressure is obtained by pouring a little mer 

 cury, or in some cases oil, into the tube ; this 

 resting in the legs of the lower bend, keeps 

 the vessel perfectly air-tight. 



Price, 75cts. 



Test Tubes and Stand. (Figs. 502 and 503, page 68.) 

 Test tubes are made of glass, and for convenience are used 

 with a stand, but sometimes test glasses are used when the 

 stand is not required. These tubes are for testing small 

 quantities of the liquid or mixture under analysis. For in- 



