526 Mr. W. A. Shenstone [March 8, 



above. It is hard, transparent to the ultra-violet rays, difficult to 

 melt, a good insulator, and insoluble in most solvents, but it bears 

 sudden changes of temperature very badly, and therefore it is not 

 easy to manipulate it at bigh temperatures. When it has been vitrified 

 by heat, however, it becomes much more tractable, and in the vitreous 

 state (vitrified silica) it is not very troublesome to deal with. 



It is about this " vitrified silica," how to prepare it and fashion 

 it into apparatus when plastic, and about its properties and uses, that 

 I am to address you to-night. 



The first obstacle met by those who wish to make vitrified silica 

 is caused by the tendency of quartz to splinter. It will not bear 

 contact with a flame. As you see, when a piece of quartz is thrust 

 into a flame it cracks and falls to pieces, and the fragments again 

 break up when similarly treated. Consequently it was very difficult 

 for the pioneer workers in silica to soften it in the flame. It is true 

 that if the quartz be broken small and heated to redness in a crucible 

 it becomes more easy to manage, but even then it gives much trouble, 

 and I should not like to say how much my first silica tube, which 

 had a capacity of about 5 cubic centimetres, had cost me for oxygen 

 and labour when it was finished. 



Fortunately, we have found that we can make non-splintering 

 silica by heating quartz in small fragments to about 1000° C, and 

 throwing them quickly into cold water. As you see, it then becomes 

 white and enamel-like, and after the treatment has been repeated, the 

 product, though still in masses, may be thrust suddenly into the 

 hottest part of an oxy-hydrogen flame without causing it to splinter 

 to the slightest extent. The preparation of this non-splintering silica 

 constitutes the first stage of the process I am about to show you. 



Another difficulty is connected with the oxy-gas burner. Vitrified 

 silica only becomes sufficiently plastic for our purpose when it is heated 

 above the melting point of platinum, and it cannot be heated suffici- 

 ently in all parts of an oxy-gas flame. What we want is not so much 

 a very large flame as one which presents a very hot spot (this is 

 situated just beyond the inner blue cone of the flame). After trying 

 all sorts of burners I have concluded that the "mixed gas" jets 

 give the best results, and the injector burner of Mr. Jackson of 

 Manchester is decidedly the best I have met with. 



The first step in the process of converting the white enamel-like 

 non-splintering silica into tubes and other vessels consists in heating 

 the ends of two small fragments of the material held in platinum 

 forceps, pressing them together whilst hot till they adhere, adding a 

 third lump to these, then a fourth, and so on until a rough rod has 

 been made, and then reheating sections of this rod and drawing it 

 out into finer rods about 1 mm. in diameter. In doing this care 

 must be taken to heat each fresh mass of material slowly and from 

 below upward in order that there may be as few bubbles as possible 

 in the vitrified product. 



A few of the fine rods of silica are next bound round a stout 



