GRADUATION OF LIQUID MEASURES. 



37 



bending of tubes is a very easy operation ; about an inch is heated 

 in the spirit flame, the tube being constantly turned round on its axis 

 in order that all parts may be equally heated, and the ends gently 



FIG. 36 



FIG. 37 (real size). 



inclined towards each other when the heated part is sufficiently soft. 

 The tube should be drawn out before it is bent, for afterwards it 

 cannot be conveniently turned. The vessel is filled with water, 

 the mouth applied to the tube . and air being forced into the flask 

 the water issues in a fine jet from the narrow orifice of the tube 5. 



- For small liquid measures common test-tubes may be employed ; 

 they are thin cylindrical vessels of glass with rounded bottoms, 

 the edges of the open end being turned outwiards. A test-tube of 

 about 12 mm width and 12 cm length is divided into cubic centi- 

 metres and half cubic centimetres up to a capacity of 10 CC ; another, 

 of 20 or 25 mm width and 2O m length, may be divided into whole 

 cubic centimetres up to a capacity of 50. 



A slip of writing paper l cm wide is pasted with gum, or better 

 with isinglass which has been dissolved in boiling water, down the 

 length of such a tube. When dry, a double thread is tied round 

 the tube under the edge, in order to suspend it to one extremity 

 of the beam of a balance, from which the scale-pan has been re- 

 moved, fig. 35. Shot or sand is put into the other scale until 

 equilibrium is restored. If the scale-pan is not very light, it may, 

 without additional weights, be heavier than the test-tube ; in 

 this case a small piece of lead or a stone is suspended by 

 the side of the test-tube, and then equilibrium is produced by 

 shot or sand placed into the opposite scale-pan. Weights are now 

 placed in the scale one by one, and each time water is poured into 



