MANIPULATION. 39 



To ttend Glass Tubing. For smooth gradual bends, use the ordinary 

 fish-tail luminous (or the Bunsen wing-top) flame; revolve the tube 

 lengthwise in the flame for a very gradual bend, and obliquely for less 

 gradual bends. For making special shapes, bend or mould the hot glass 

 with a cold iron. 



To Make Capillary Tubes and Rods. Hold the smallest available 

 glass tubing in either flame, revolving it until soft, and then pull apart 

 the two ends. The fineness of the tubing can be controlled by the degree 

 of heating and rapidity of the drawing-out. The same method applies 

 to solid capillary filaments, though for most purposes the lighter tubes 

 are preferable. To keep the capillaries straight, pull up and down, not 

 to right and left. 



To Smooth Rough Glass Ends and Edges. Hold the rough parts in 

 the Bunsen flame until they fuse smooth. Small tubing may be thrust 

 at once into the flame, but large tubing and glass plates, etc., must be 

 brought into it very cautiously. The rough ends of fine capillary tubes 

 (which may be cut across with scissors) maybe smoothed by careful rub- 

 bing on an oil-stone, or on a piece of ground glass, or by cautious fusing. 



To Seal the End of a Glass Tube. If held in a hot Bunsen flame (the tip 

 of the inner cone is the hottest part) and revolved, it will fuse itself to- 

 gether, closing perfectly. Or the tube may be drawn out to a capillary 

 point, and after it is adjusted in some desired position, the capillary point 

 may be sealed in a moment by a gas- or spirit-lamp flame. 



To Prevent Evaporation from a Free Water or Other Surface. If a 

 water-surface, place on it a film of oil, such asparaffine oil (or some other 

 which will not become gummy or rancid on exposure to air), which is a 

 very perfect preventive. If a flower-pot or similar object, cover it with 

 dentist's rubber sheeting, which is a very good though not perfect pre- 

 ventive of evaporation. It is said also that cleaning, drying, and paint- 

 ing the surface of the pot with melted paraffine (which may easily be 

 peeled off after the experiment) efficiently prevents evaporation. 



To Graduate a Tube Temporarily. If only a relative graduation is 

 needed, proceed thus. Stretch a fine thread by a wire spring, much as a 

 bent bow is strung, and on it place a drop of liquid India ink, which will 

 spread by capillarity ; place the tube beside a mm. measure, and, touch- 

 ing the thread to the glass, even marks of any desired fineness may be 

 made at any desired intervals, or a pasteboard mm. scale, or a paper mm. 

 scale on a wooden strip, may be wired to the tube. If a tube graduated in 

 definite units is needed, it is better to use a ready-graduated burette or 

 pipette, in the absence of which a measured quantity of water is to be 

 drawn into the tube by sucking on a rubber tube forced over its upper 

 end ; the top and bottom positions of the liquid are to be marked, and 

 intermediate capacities obtained and marked by the mm. scale and thread 

 as above. Tubes of disabled thermometers (or, better, the scales of milk- 



