OF CENTRAL CANADA PART I. 41 



moved backward from the flame, and the oxidizing process again 

 established. 



Reactions : Certain reactions of the more commonly occurring 

 constituents of mineral bodies have already been mentioned in illus- 

 tration of the various operations given above. In the present place 

 a few additional reactions are described, and the whole are arranged 

 in systematic form.* 



A. DETERMINATION OF THE CHEMICAL GROUP TO WHICH A MINEARL 



MAY BELONG. 



In the examination of a mineral by the blowpipe, it is advisable to 

 look first to its general chemical nature or, in other words, to deter- 

 mine the chemical group to whicn it belongs and afterwards, to seek 

 for the base or bases which it may contain. The more important 

 chemical groups of natural occurrence, comprise : Sulphides, Arsenides, 

 Chlorides, Fluorides, Oxides, Sulphates. Silicates, Carbonates, Borates, 

 Nitrates, Phosphates, and Arseniates. The group of simple Oxides 

 can only be determined by negative characters, but the other groups 

 are easly recognized by a few simple experiments. 



Experiment 1. Fuse the substance, in powder, with 2 or 3 vols. of 

 carb. soda and a little borax, in a good reducing flame, on charcoal. 



This experiment serves directly for the detection of Sulphides, Sul- 

 phates, Arsenides, and Arseniates. 



a. A strong odour of garlic is emitted : Arsenides and Arseniates. 

 The former possess a metallic aspect, and emit the garlic odour when 

 ignited per se. The latter never exhibit a metallic aspect. As occur- 

 ing in nature, arseniates are mostly of a green, blue, or red colour, 

 depending on the nature of the base. 



b. A reddish or dark mass is produced. This, when moistened 

 and placed on a bright silver coin or on a glazed visiting card, forms 

 a dark stain. The moistened mass smells also of sulphuretted hydro- 

 gen : Sulphides and Sulphates. The former possess a metallic aspect, 

 or, if the lustre be non-metallic, the streak is always distinctly col- 

 oured, f With few exceptions, they omit an odour of burning brim- 

 stone (sulphurous acid) when ignited per se ; and in the open tube, 



* A more complete method for the rapid determination of the chemical nature and composi- 

 tion of mineral bodies will be found in the author's BLOWPIPE PRACTICE, pages 60-65. 



t Certain specimens of Zinc Blende are the only exceptions to this, so far at least as regards 

 naturally occurring minerals, to which alone the statements of the text apply. 



