ge 
fi 
Zinc, as a Covering for Buildings. 249 
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It is alledged that a potsonous suboxide of zinc is dissolved in the 
water, which renders it unfit for cooking, and impairs its properties 
for washing. On this point I have consulted the ablest modern 
writers on sfeowitisy, Brande, Turner, Thomson, Berzelius, and 
others. ‘The oxides of zinc seem not to have been’ much studied. 
The principal one known, and perhaps the only one certainly known, 
is the white oxide, (sometimes called the flowers of zine,) which is 
quite zxsoluble in water, and hence could not vitiate its properties. 
Berzelius thinks there are two others, the suboxide and the super- 
oxide. 
The suboxide is the gray coating formed on the surface of zine 
by exposure to the weather, and this i is the substance which, it is 
said, is dissolved and mixed with the water, which falls from a zinc 
nial thereby impregnating it with deleterious properties. This opin- 
ion, so far as I can learn, is unsupported by any writer on chemistry. 
Turner says, ‘zinc undergoes little change by the action of air and 
moisture.”” Aikin’s Chemical Dictionary, a work of merit and au- 
thority, says, “ the action of the air upon zinc, at the common tem- 
perature, is very slight; it acquires a very thin superficial coating of 
gray oxide, which adheres to the metal and prevents any further 
change.” The statement of Thomson is, that zinc, when exposed 
to the air, soon loses its lustre, but ‘‘scarcely undergoes any other 
change.” The account given by Berzelius, the ablest chemist of 
the age, is very explicit and much to the point. He says, ‘“ this 
oxide is formed on the surface of zinc which remains a long time 
exposed to the contact of the air. It has a dark gray color when 
moistened, but by drying becomes of alight gray. Ordinarily it 
forms a thin crust on the surface, which neither increases nor expe- 
riences any change in the air; but acquires great hardness, and re- 
sists, better than the metal itself, the mechanical and chemical action 
of other bodies. A piece of zinc sufficiently suboxidized at the sur- 
face, dissolves with extreme slowness in the acids, and only at the 
boiling temperature.” 
Such are the opinions of chemists, and particularly of Berzelius, 
whose unrivalled skill and accuracy in chemical analysis, have been 
the admiration of all cotemporary chemists. 
The opinion of Dr. G. is considerably at variance with those now 
adduced. 1 think he has not stated very fully, and certainly not very 
satifactorily, the reasons on which it is founded. He mentions, how- 
ever, as a proof that this suboxide is dissolved in water from zine 
Vout. XXXI.—No. 2 32 
