HIGH FARMING. 77 



The best form of burner we have ever seen is that introduced 

 by Mr. Spence, of England, the fire-brick hearth of which is about 

 40 feet long by 6 inches wide. It is fired from below, and receives 

 the necessary air through an opening in the front, regulated by a 

 damper. This oven will successfully burn pyrites in fine powder, 

 perfect combustion being ensured by introducing them at the op- 

 posite end to the fire and gradually pushing them to the hottest 

 parts. When once they have become fully ignited, no further fuel 

 of any kind is required, as they will continue to bum until all the 

 sulphur is exhausted. 



At the mouth of the flue or chimney of these ovens, are placed 

 cast-iron "nitre pots" containing a mixture of nitrate of soda and 

 sulphuric acid, and evolving dense nitric acid vapors. Under the 

 combined influence of the intense heat and the current of air passing 

 through the furnace, the pyrites undergo total decomposition ; the 

 sulphur being driven off in the form of vaporous sulphurous acid, 

 and the iron being transformed into oxide. When the sulphurous 

 vapors arrive at the flue, they meet with those emanating from the 

 nitre pots, and the two, immediately combining, pass off through 

 large conductors built of lead and lined with brick, known as 

 " Glover's towers," into large leaden chambers, where they are 

 brought into contact with a considerable body of steam. 



These chambers are constructed entirely of lead, weighing from 

 six to seven pounds per square foot, and are generally put up in sets 

 of three, connected by syphon and cistern arrangements for drawing 

 off and storing the acid, as it is made. They are built upon a frame- 

 work of timber, supported by iron columns, and all round their 

 sides are placed small glass windows, through which the various 

 colors assumed by the vapors, as the manufacturing process devel- 

 opes itself, may be plainly seen. At regular intervals between these 

 windows, are found leaden syphons, which dip into small leaden 

 tanks within the chamber, and permit of samples of the acid being 

 drawn as required. 



Endless discussion has taken, and continues to take place concern- 

 ing the best size to be adopted for a chamber. 



