Zinc, as a Covering for Buildings. 251 
_ This objection is based upon the fact that zinc melts at a low tem- 
perature ; and in case of fusion, leaves the wood work of the build- 
ing unprotected. This objection is rather specious than real. Zinc 
melts at the temperature of, about 700° Fahr. or a little below red 
heat. Whenever, therefore, the heat from adjacent buildings is any 
thing less than that of redness, zinc would afford as complete pro- 
tection as copper or iron. When the heat has reached the melting 
point of zinc, which it seldom would do except in the most compact 
parts of cities, very little confidence could be placed in the protec- 
tion. of iron or copper. The dry wood work of the roof, under a 
covering of red hot iron, with air enough for combustion circulating 
through openings and crevices, would soon be in flames; and when | 
once in flames it would be extremely difficult to extinguish it by the 
application of water. It would be applied with great disadvantage 
to the under side of the roof, and almost to no purpose at all upon 
the top. If therefore the heat, in any case, should become so in- 
tense as to melt zinc, the probability of protection from iron or cop- 
per will be but small. 
Complete protection against fire is perhaps unattainable ; at least 
we can never be sure that we have attained it. In the progress of 
the arts, great improvements no doubt will be made in the mode of 
defence against the attacks of this destroyer. Iam not aware that the 
following construction for a roof has ever been tried. For cheapness, 
tightness, durability and resistance to fire, it seems to be well desery- 
ing the attention of builders. Let the rough boards of the roof, 
(and the rougher the better,) be covered with a thick coating of 
common lime mortar,—then lay down the rids, if I may so call 
them, for the zinc plates,—then cover the whole with zinc, according 
to the most approved method of applying it. Such a roof would be 
in no danger of leakage, unless the water accumulated upon it so as 
to stand above the ribs, in which case no roof would be tight unless 
it were calked or soldered throughout. This covering, if I am 
.tightly informed, would be nearly as cheap as slate—quite as cheap 
as tin, cheaper than iron, and more than three times cheaper than 
copper ; and would at the same time resist fire much better than 
either of them. A heat that would melt down the copper and iron, 
would, of course, melt the zinc, but would leave the mortar unin- 
jured. The peculiar advantage of the mortar is, that it is infusible 
except at a very high temperature, while the closeness with which 
it adheres to the wood work is such as to exclude the air and thus 
