On the Common Blowpipe. 319 
roofs are furnished in this great metropolis? It may be said, that 
they have used a bad article. But, I repeat, does not Crocker & 
Brother’s zinc, does not the best foreign article, come to the New 
York market? Where have purchasers a better opportunity of se- 
lecting good zinc, where have builders a better opportunity of ex- 
perimenting and ascertaining the best material for roofing? Is it 
probable that men who have gone deeply into the business of roof- 
ing with zinc, would readily abandon it, if they could sustain it ? 
Would proprietors sustain the expense of tearing off the zinc and 
substituting some other material, if there were any other better 
method of managing? Would they not first resort to the expedient 
of mending? This last question I can answer from personal know- 
ledge, that mending of zinc roofs has in some cases been nearly 
equal in expense to half the first cost. I am quite satisfied, that if 
my friend, Prof. Caswell, will review the whole matter of zinc roofs, 
he will come to the conclusion that notwithstanding the superior 
ducts of Messrs. Crocker, Brother & Co. there are still difficulties in 
the use of zinc as a roofing material that are not entirely imaginary. 
Art. XIII.—On the Common Blowpipe ;* by J. W. Batter, Act- 
ing Prof. Chem. &c. U.S. Mil. Acad., West Point. 
On account of its portability, the facility of its use, and its nu- 
merous applications, the blowpipe ranks as one of the most valua- 
ble instruments of chemical research. It consists essentially of a 
tube, generally bent and having a small orifice, by means of which 
a current of air, from the lungs, may be forced through the a of 
a lamp or candle. 
Fig. 1. 
satis teh 
Fig. 1, shows the simplest form of the blowpipe, and such ones are 
easily made from glass tube in case of necessity, but they are incon- 
venient when made of this material ¢ on account of their easy fusibility. 
vest Point, and being 
solely intended as an introduction ad the use of the sowie, were e pu ae ely made as elemen- 
ossi! Pr seful to other students.— 
2 
