_Use of Lead-Glass._--When lead-glass is to be used, the blowpipe flame should be in good adjustment and the glass should not be allowed to approach so near to the blue cone as to be blackened. Slight blackening may often be removed by heating the glass in the extreme end of the flame. Lead-glass articles tend to be rather more stable than similar articles of soda-glass. _Combustion-Glass._--This may be worked more easily if a small percentage of oxygen is introduced into the air with which the blowpipe flame is produced. If the air is replaced entirely by oxygen there is a risk of damaging the blowpipe jet, unless a special blowpipe is employed. _Internal Seal._--There are two ways of making these, one, in which the inner portion of the tube is fused on to the inside of the bulb or tube through which it is to pass, an opening is made by bursting and the outer tube is joined on. This is a quick and in some ways more satisfactory method than the other, in which there is no separate inner piece. _Rubber Blowing Tube._--In complicated work it is often convenient to use a thin rubber blowing-tube which is connected with the work either by a cork and piece of glass tubing or by fitting over a drawn-out end. The use of such a blowing-tube avoids the inconvenience of raising the work to the mouth when internal air-pressure is required. One end of the rubber tube is retained in the mouth during work. _General Notes._--A large amount of glass-blowing is spoiled through carelessness in arranging the work beforehand. The student should have every detail of his manipulation clearly in mind before he commences the work; he should not trust to evolving the method during the actual manipulation. Undue haste is another fruitful source of failure. Practically every operation in glass-blowing can be carried out in a perfectly leisurely manner, and it is better to err rather on the side of deliberation than on the side of haste. If, as will doubtless happen at times, a piece of work gives trouble and it is necessary to pause and consider the whole question, or if for any other reason it is necessary to stop during the construction of a partially finished join or other operation, great care should be taken not to allow the work to cool. A large, brush-like flame may be produced by increasing the amount of gas admitted to the blowpipe, and the work should be held just in front of the current of hot air produced by such a flame. It will then be possible to continue work on this without causing it to crack when further heat is applied. As time goes on, the student will find an increasing confidence in his ability to manipulate the soft glass, and with increasing confidence will come rapidly increasing power of manipulation. Perhaps the greatest obstacle to success in glass-blowing is undue haste in manipulation. INDEX Absorption bulbs, 21, 23. Airtube, flexible, 8, 102. Alarm thermometer, 45. Annealing, 7, 60.