170 
PREPARATION OF OXIDE OF ZINC. 
difficulties which had been previously experienced in the 
process. The apparatus employed by Mr. Midgley is a 
large muffle, which is heated to redness in a furnace of suit- 
able construction. The draught of air necessary for sup- 
porting the combustion is conveyed from the muffle by a 
tube passing through the top of the furnace and terminating 
in a vessel containing water, in which the portion of oxide 
which is carried off in the current of hot air is retained. 
With an apparatus of this kind he makes a hundred weight 
or two of the oxide at a time, by a continuous process, the 
zinc being introduced into the muffle from time to time as 
the combustion proceeds. Any particles of metallic zinc 
that may remain mixed with the oxide are subsequently se- 
parated by a sieve. The author states that the zinc or 
spelter of commerce is now made extremely pure, and 
yields by combustion a white oxide, which is free from cad- 
mium or other metals. He expresses an opinion that the 
oxide obtained by this process here described, is more effica- 
cious when used in the form of ointment, than that made 
by any of the processes which have been published in the 
modern Pharmacopoeias. In confirmation of this, he al- 
ludes to a statement published some years ago by Mr. Red- 
wood, from which it appeared that the so-called oxide of 
zinc of commerce, contained large quantities of water, and 
of carbonic or sulphuric acid. He also recommends the use 
of oxide of zinc made by combustion, as a subtsitute for 
white lead in the preparation of paint. Among the advan- 
tages which he conceives would result from this substitu- 
tion, are ; the superior preservative effect of the oxide of 
zinc, the fact of its not being altered in colour by sulphuretted 
hydrogen or other gases, and the avoidance of those inju- 
rious effects upon the health which are experienced by 
the workmen employed in the manufacture of white lead, 
Mr. Squire inquired if Mr.JMidgley had practically tried 
the use of oxide of zinc as a substitute for white lead in 
paint. He (Mr, S s )had tried it some years ago in his labo- 
