OF CENTRAL CANADA PART I. 31 



part of the glass. A small spirit-lamp may be made by passing a piece 

 of glass tubing of about an inch in length, to serve as a wick-holder, 

 through an orifice in the cork of a short, flat bottle. When the lamp 

 is not is use the wick should be covered with a glass or other cap to 

 prevent the evaporation of the spirit. A mineral may also be exam- 

 ined for water, though less conveniently, by igniting it before the 



blowpipe-flame in a piece 

 of open tubing, as shown 

 in FIG. 35. To prevent 

 the tube softening or 

 melting, a strip of plati- 

 num foil may be folded 

 FlG - 35 - round it where the test- 



fragment rests. The latter is pushed into its place by a thin iron 

 wire. The moisture condenses on each side of the test-matter. 



(3) Treatment with Nitrate of Cobalt : This operation serves, in 

 certain cases, for the detection of alumina, magnesia, oxide of zinc, and 

 some few other substances; but it is not applicable to deeply coloured 

 or easily fusible bodies, nor to such as possess a metallic lusfere or 

 coloured streak. A fragment of the substance, under treatment, is 

 reduced by the hammer and anvil, and afterwards by the use of the 

 agate mortar, to a fine powder. This is moistened with a drop of the 

 cobalt solution (nitrate of cobalt dissolved in water), and the result- 

 ing paste is strongly ignited on charcoal by being held about an inch 

 before the point of the flame, fusion being carefully avoided. Thus 

 treated, alumina assumes on cooling a fine blue colour; magnesia (and 

 the comparatively rare tantalic acid), a flesh-red tint; baryta, a dull 

 brownish-red colour ; oxide of zinc, bin-oxide of tin, antimony oxides, 

 a green colour. With other substances, a grey, blueish-grey, 

 brownish-black, or other indefinite coloration is produced, unless 

 fusion take place, in which case a glass may be obtained, coloured 

 blue by the dissolved oxide of cobalt. 



(4) Roasting : Tne principal object of this operation is the elimi- 

 nation of sulphur, arsenic, and certain other volatile bodies, from the 

 mineral under examination, as these prevent the reduction of many 

 substances to the metallic state, and also mask, to some extent, their 

 other characteristic reactions. By roasting, the substance is not only 

 deprived of sulphur, &c., but is also converted into an oxidized con- 



