1901.] 



on Vitrified Quartz. 



527 



platinum wire, or twisted into a spiral whilst soft (Boys' and Dufour's 

 method), and heated in the flame till the sides of the rods adhere. 

 The uncouth tube thus produced is reheated, drawn out, and closed 

 at one end ; a bulb is blown on the closed end in the usual manner, 

 and this, when again drawn out, gives a fine and fairly regular tube 

 which can be lengthened by adding silica to one end of it, blowing a 

 new bulb from this and drawing it out as before. 



The enlargement of the small bulbs was, at first, rather difficult. 

 My earliest attempt consisted in adding a small lump of silica to 

 one end of a bulb, softening this in the flame and expanding it by 

 blowing. It is not impossible to succeed in this way, though the 

 vessels so produced are apt to be uncouth in appearance. 

 But the process is unsatisfactory, owing to the fact that 

 often the thinner parts of the bulb which immediately sur- 

 round the mass to be expanded become hotter and softer than 

 the latter. When this happens the bulb bursts, and as it can 

 only be repaired by the addition of fresh lumps of silica, 

 the process is apt to be very tedious and expensive. After 

 many failures, it occurred to me that I might develop the 

 bulbs by applying thin rings of silica as thown in Fig. 1, 

 heating them until they begin to spread, and then expand- 

 ing them by blowing. This method gives satisfactory 

 results. By it we can produce long tubes and other appa- 

 ratus like those exhibited to-night, if not at a very quick 

 rate or very low cost, yet with certainty and very much 

 more quickly than before. 



When once a tube of silica has been made, it can be 

 worked in the flame as easily, though not as inexpensively, 

 as glass. Such a tube can readily be thickened by adding 

 fresh rings of silica, and it can be drawn out to various 

 degrees of fineness and sealed hermetically, whilst all 

 kinds of joints can be made easily. In one respect silica 

 is easier to work than glass ; it never breaks when thrust 

 into the flame and finished apparatus needs no annealing. Fig 1. 



One precaution must be taken. The eyes must be 

 protected by black spectacles, and the glass of which these are made 

 must be very dark ; so dark that white hot silica does not look very 

 bright when viewed through it. 



I have spoken of silica as being easy to work, but I do not mean 

 you to understand that it is easy to do what you see Mr. Lacell 

 doing to-night. It is not easy to perform any operation of this sort 

 with his wonderful precision, and especially it is not easy to work 

 under the conditions enforced upon him now, for he can see nothing of 

 the effects he produces and must adapt his manipulation to my remarks, 

 although he can hear the latter only very imperfectly. 



