Zirconia for the Oxy-hydrogen Light. 209 
its position in the optical axis of the apparatus, it is thrown 
into operation with comparative facility when cylinders con- 
taining the compressed gases are available, and it has sufficient 
intrinsic brilliancy for the majority of experiments. e diffi- 
culties in the way of its use are however serious, and it is very 
desirable that they should be lessened. They arise chiefly 
rom the volatility of the calcium oxide at the intensely high 
temperature employed. The volatilized material depositing 
on the condensing lenses prevents the passage of the luminous 
rays, and the cavity formed in the cylinder of hme at the spot 
where the flame impinges soon interferes with the brilliancy of 
the light; this necessitates a change in the position of the lime 
cylinder to present a new surface to the action of the flame, 
and this in its turn implies a distraction of the attention of the 
experimenter, which interferes seriously with the satisfactory 
management of his subject. Though the attempt is made to 
trivances, they are stil] unsatisfactory in their action. Another 
serious objection i is the necessity of placing the cylinders in a 
closed vessel when not in use to protect them from the action of 
the air. 
-magnesium light is similar to the preceding, differ- 
ing seg in the substitution of a cylinder or pencil of magne- 
sium oxide for calcium oxide, and the light emitted is of equal 
brilliancy. Following the instructions given for the prepara- 
tion of these cylinders, I have taken the greatest pains to pro- 
cure samples of magnesium oxide of the utmost purity. I have 
also tried various methods for its preparation, among which the 
combustion of the metal in oxygen may be men ntioned, but 
failure has thus far attended all efforts to make pencils or 
cylinders which could withstand the intense heat of the flame 
of the mixed oxygen and hydrogen gases without undergoing 
volatilization. The pencils obtained were fully equal in this 
respect to those of calcium oxide; but, I did iti find any 
superiority that repaid the trouble of their prepara 
he oxy-zirconium light produced by the action ore the flame 
of mixed oxygen and hydrogen gases on a cylinder of zirconium 
elds meets all the requirements of the case in question. It 
has the intrinsic brilliancy, the invariable brilliancy, the fixity 
of position in the optical axis of the apparatus, and it does not 
volatilize under the heat employed. The condensing inneee 
ain free from deposit, and after the light is once adjust 
the experimenter can carry on his demonstrations without the 
distraction of his sop that attends the use of the’ other 
lights. All that is necessary is according to the size of the 
reservoirs of compressed gas to open the cocks a little as the 
pressure diminishes. There is also no necessity to remove 
