68 CHEMICAL PROPERTIES OF MINERALS. 



during the blowing ; the moisture, unless thus removed, is 

 often blown through the small aperture and interferes with 

 the experiment. The air chamber in figure fD2 is a cylin- 

 der, into which the tube a b c is screwed at c, and the small- 

 er piece d e f, at d. For the convenience of packing it 

 away, there is a screw at b. The part b c, after unscrewing 

 it, may be run into the part a b, through the large end, (a,) 

 and screwed up again, and thus it is half the length it has 

 when arranged for use. The mouth piece e f screws off, 

 and is made o£ platinum in order that it may be cleaned when 

 necessary by immersion in an acid. The best material for 

 the blowpipe is silver, or if a cheaper material is desired, 

 tinned iron with the piece efof brass. Brass gives a dis- 

 agreeable smell to the moist fingers. 



In using the blowpipe, it is necessary to breathe and blow 

 at the same time, that the operator may not interrupt the 

 flame in order to take breath. Though seemingly absurd, 

 the necessary tact may easily be acquired. Let the student 

 first breathe a few times through his nostrils, while his cheeks 

 are inflated and his mouth closed. After this practice, let 

 him put the blowpipe to his mouth, and he will find no diffi- 

 culty in breathing as before ; while the muscles of the in- 

 flated cheeks are throwing the air they contain through the 

 blowpipe. When the air is nearly exhausted, the mouth may 

 again be filled through the nose without interrupting the 

 process of blowing. 



A lamp with a large wick, so as to give a broad flame, 

 and fed with olive oil, is best ; but a candle is more conve- 

 niently carried about when travelling. The wick should be 

 bent in the direction the flame is to be blown. 



The flame has the form of a cone, yellow without and blue 

 within. The heat is most intense just beyond the extremity 

 of the blue flame. In some trials, it is necessary that the 

 air should not be excluded from the mineral during the ex- 

 periment, and when this is the case, the outer flame is used. 

 The outer is called the oxy dating* flame, and the inner the 

 reducing flame. 



Explain the structure and mode of use. What is said of the flame 

 of a candle before the blowpipe 1 Which is the oxydating, and which 

 the reducing flame ] 



* It is so called because when thus heated, oxygen, one of the con- 

 stituents of the atmosphere, combines in many cases with some parts 

 •f the assay (or substance under experiment.) 





