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 pro- 

 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. Bailey, Act- 

 ing Prof. Chem. he. 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 flame of 

 a lamp or candle. 



Fie. 1. 



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. 



' These notes were drawn up to form part of the com-se of chemistry at West Point, and being 

 solely intended as an introduction to the use of the blowpipe, were purposely made as elemen- 

 tary as possible— but it is supposed the directions may be useful to other students ^Ed. 



