OF CENTRAL CANADA PART I. 37 



surface after subjection to an oxidating flame. Copper becomes covered 

 with a black film, and tin with a white crust. Lead and bismuth 

 volatilize more or less readily, and deposit on the charcoal a yellow 

 coating of oxide. Antimony is rapidly volatilized with deposition of 

 a dense white incrustation on the charcoal. It is not, of course always 

 necessary to subject the test-substance to a previous roasting (Opera- 

 tion 4, above) but it is always safer to do so. Sulphur in most, and 

 arsenic in all cases, must be driven off by this preliminary treatment 

 before the actual process of reduction is attempted. 



When the metal to be reduced belongs to the second group, or if 

 the amount of fusible metal in the test-substance do not exceed 4 or 

 5 per cent., the operation is performed as follows. A small portion 

 of the substance in powder subjected previously to the roasting pro- 

 cess, if it contain sulphur or arsenic is mixed with 3 or 4 volumes 

 of carbonate of soda (or neutral oxalate of potash, or a mixture of 

 about equal parts of carb-soda and cyanide of potassium the latter, 

 it must be remembered, a highly poisonous substance), and the mix- 

 ture is exposed on charcoal to a good reducing flame, until all the 

 alkaline salt has become absorbed. Some more of the flux is then 

 added and the operation is repeated until the whole or the greater 

 part of the test-matter is also absorbed. The charcoal at this spot is 

 finally separated by a sharp knife-point and carefully ground to powder 

 in a small agate mortar or porcelain capsule, whilst a fine stream of 

 water is protected upon it from time to time, until all the carbonaceous 

 and other non-metallic particles are gradually washed away. For this 

 purpose, the mortar or capsule may be placed in the centre of an 

 ordinary plate ; and if the operator be not provided with a chemical 

 washing-bottle, he may use a small syringe, or, still more economically, 

 a simple piece of glass tubing, five or six inches in length and about 

 the fourth of an inch in diameter, drawn out at one end to a point. 

 This is filled by suction, and the water expelled, with the necessary 

 force, by blowing down the tube. The metallic grains or spangles 

 obtained by this process must be examined by the magnet. Those 

 of iron, nickel and cobalt are magnetic. Sometimes, however, when 

 but a trace or very small percentage of reducible metal is contained 

 in the test-substance, its presence is only indicated by a few metallic 

 streaks on the sides and bottom of the mortar. Metallic markings 

 of this kind can be removed by a piece of pumice. 



