1 6 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



the process of calcination or burning of iron ore, and the more 

 important chemical actions involved. Blackband ironstone 

 contains a considerable quantity of carbonaceous matter, the 

 amount varying from lo to 50 per cent., and before the ore is 

 smelted in the blast furnace for the production of cast iron, it 

 is subjected to a preliminary process of burning or calcining, 

 with the object of getting rid of this carbonaceous matter, water, 

 and other volatile substances. In open roasting, the process 

 employed by the Shotts Iron Company, the ore is simply spread 

 in heaps or " bings," set fire to, and allowed to burn itself out. 

 The ore is broken and heaped up to a height of about 8 feet 

 over an area of about 2 acres ; one edge of the heap is first mixed 

 with coal, and the heap or " bing " set fire to along that edge ; 

 it then burns gradually throughout the entire extent, the burning 

 taking from two to three months to complete. 



In addition to this carbonaceous or coaly matter, however, 

 the ore contains about i per cent, of sulphur, and during 

 burning the greater part of this is set free in the smoke as 

 "sulphurous acid," the chemical substance to which the familiar 

 sharp pungent smell of burning sulphur is due. This sulphurous 

 acid gradually combines with oxygen gas from the air, especially 

 if the air is moist, to form sulphuric acid- — the substance known 

 in the concentrated state as "oil of vitriol." Both these sub- 

 stances, but especially the sulphuric acid, are exceedingly 

 hurtful to vegetation if present in any quantity in the air. 

 Although the quantity of sulphur burnt off from the ore — less 

 than I per cent. — may not seem large, yet when we remember 

 the enormous quantities of ore roasted, it is seen that a very 

 large quantity of sulphurous vapours is being poured into 

 the air during the time the operation is in progress. It was 

 not enough, however, to prove that large quantities of sulphurous 

 vapours were given off at the burning bings ; it had to be 

 shown that by the time the smoke reached the plantations it 

 still contained, even although much diluted by mixing with the 

 air, sufficient sulphurous fumes to cause the damage complained 

 of, and further, that the damage was due to the fumes and to 

 nothing else. The amount of smoke which reached the 

 plantations depended obviously on a considerable variety of 

 circumstances — the distance of the woods from the burning 

 bings, the direction of the prevailing winds, whether the 

 plantations stood at a higher or lower elevation than the 



