THE LIME-LIGHT 69 



repeated by subsequent writers. Were it only true, all diffi- 

 culties would be solved ; but I am sorry to have to dispel 

 such expectations, after frequent and exhaustive experiments, 

 as regards any zirconia hitherto commercially obtainable. 

 My own hopes were high after reading the opinion of the late 

 Dr. Draper of New York, 1 that zirconia equalled lime in 

 ' intrinsic brilliancy ; ' but I can only come to the conclusion 

 that neither he nor Continental physicists who have so praised 

 it, ever really knew what a good light is, as I understand it. 

 I have tested three different zirconia samples of English 

 manufacture, and three of Continental (including one from 

 Schuckardt of Gorlitz, stated to be prepared especially for the 

 lantern). The result was the same in all the light was 

 distinctly reddish in colour, and far inferior to that of a 

 lime cylinder with the same jet. Mr. H. G. Madan was kind 

 enough to test the matter photometrically, with the result 

 that the best of these zirconias only gave a light of 1 : 2*88 

 compared with lime. I have since ascertained that Du 

 Motay's own pencils really gave about the same results. 



Zirconia does decidedly better when used in very thin 

 discs, instead of the jet playing on the end of a cylinder; 

 for it is most extraordinary for its non-conducting power, 

 and the most powerful jet will only illuminate a small surface 

 and for a small depth in the pure material. The best 

 substitutes for limes I have been able to obtain by pur- 

 chase are a mixture of zirconia with a small quantity of 

 some other substance probably alumina prepared under 

 the superintendence of Dr. Linnemann by Smith and Hamsch, 

 of 4, Stallschreiber-Strasse, Berlin, in discs about | in. in 

 diameter and -^ in. thick, held in platinum capsules mounted 

 at the end of a brass rod. The light is not equal to that of 

 lime, but is very fair, and nearly white. The discs will stand 

 a great deal of work, and are very convenient for many pur- 



1 Dr. Draper's own process for purifying zirconia, and his observations on 

 its use, will be found in the American Journal of Science, xiv. 208. 



