io6 



Laboratory Arts 



by heating the end in a large blowpipe flame, and, when it is 

 softened, introducing a carbon cone, and gently pressing while 



rotating it against the softened edge. 

 This gives a smooth edge to the 

 end of the tube. 



The instrument is supported by 

 a retort stand (see Fig. 94), a ring 

 being placed round the upper portion 

 of the upright tube, and a small 

 piece of brass, having a V-shaped 

 depression drilled in its centre, 

 forming the base support. 



As an alternative method the 

 four side arms may be sealed into 

 the wide upright tube, but much 

 more risk of breakage is entailed 

 by this method, owing to the diffi- 

 culty of keeping every junction 

 equally hot until the whole is com- 

 pleted a difficulty not existent in 

 the device described above, as the 

 whole junction is more or less 

 under the flame until completed. Provided the jets are small 

 no disadvantage accrues from the narrow supply tube, as its 

 sectional area is greater than the sum of the areas of the jets. 



EXERCISE n. Seal into a 6-^-mm. tube a piece of i-mm. 

 bore tubing, (a) at right angles, (b) obliquely. 



Little instruction will be needed for this exercise beyond the 

 statement that, in each case, the thermometer tubing should be 

 blown out, by successive heatings and blowings to the shape indi- 

 cated in Fig. 95, being finally blown out from AB. This enables 

 the tube to be treated exactly like one of ordinary bore. 



FIG. 94.-Barker's mill. 



EXERCISE 12. To make an " internal seal." 



This exercise is designed for the illustration of a process 

 necessary in the construction of a filter pump. Take a piece of 

 i5-mm. bore tubing, blow a bulb on the end, or close hemispheri- 

 cally, blowing out from this again a 5-7 mm. diameter spherical 

 bulb, which is to be cut off, leaving only the flanges projecting. 

 Close the wider end with a cork. 



