150 ON GUTTA-PERCHA AS A PERMANENT STOPPING. 



failure : I therefore, in the mean time, made trial of 

 a variety of other substances, which it would be 

 now superfluous to enumerate ; for, although I made 

 some tolerably good specimens of cement, none of 

 it came up to my idea of what it might be. At 

 last I succeeded in getting some silica prepared for 

 me from the fluoride of silicon by Messrs. Morson, 

 of Southampton-row, which, after being subjected 

 to a careful purifying process (for it was very dirty 

 as sent to me), I found to be just what I required. 

 Messrs. Morson, however, refused to supply me 

 with any more of it, on account of its being so 

 troublesome to prepare, and I was equally unsuc- 

 cessful with other parties. In the mean time, I pre- 

 pared some silica from the silicate of potash, which 

 answered pretty well, being very pure and white ; 

 but it was too compact and gritty to please me, and 

 did not whiten the gutta-percha sufficiently. Hope- 

 less of procuring it from others, I at length resolved 

 to prepare some myself, from the fluoride of silicon, 

 and I find it by no means a difficult process, although 

 requiring considerable care and attention. 



As I take especial pains to keep it free from all 

 impurities, I find that what I prepare myself is a 

 much better article than that which I obtained 

 from Messrs. Morson ; in fact, it surpasses my most 

 sanguine expectations. I need not describe the 

 process for obtaining it, as it may be found in works 

 on chemistry ; but I would recommend no one to 



