Manufacture of Sulphat of Iron. 321' 



For three or four years past they have adopted a more 

 expeditious method of decomposition, which was discover- 

 ed in the first place by accident. They break the ore into 

 much smaller fragments, three inches and less in diameter, 

 and throw them into a convenient heap, taking care to leave 

 air holes at the base, so as to allow the air to pass freely 

 through the heap. On applying water the decomposition 

 commences, and so much heat is evolved, as presently to 

 raise the temperature of the heap to such a degree as to 

 charr wood, boil water, sublime sulphur, he. Great quan- 

 tities of sulphurous acid gas are evolved during the process, 

 and in the course of three or four weeks the whole becomes 

 deintegrated and ready to fall into the state of powder. It 

 then by lixiviation with water, yields all its copperas at once ; 

 the process is performed in a plank cistern. 



When I visited the mine last summer one of these artificial 

 volcanoes happened to be burning. The sulphurous acid 

 produced had run down the side of the hill below, and kill- 

 ed the grass and leaves of the trees for several rods, as com- 

 pletely as though they had been scorched by fire. It was 

 even dangerous to approach it except on the windward side. 

 I thrust a stick into it and it was charred to blackness in a 

 few minutes. I obtained needle-shaped crystals of sulphur 

 which had evidently been formed on the external surface of 

 the heap by sublimation- I was informed that the sulphur 

 usually melted and ran down into the cavities, and that it 

 frequently burned with flame in various parts of the heap. 



The manufactory in which the processes of evaporation 

 and crystalization are performed, is placed on the declivity 

 quite below the mine. This gives great facility to all the 

 operations, allowing the various reservoirs to be so arrani9::ed 

 one above another that the liquor may be transferred from 

 one process to another merely by means of a trough. 



The bottoms of the evaporating vessels are of lead, 

 and about ten feet square ; the sides are of wood about 

 three or four feet high. The bottom is supported by a 

 number of parallel brick walls, placed at a small distance 

 from each other. The avenues or arches between these 

 walls communicate at one end with the arch in which the 

 fire is placed, and at the other with the common flue. 



The ore is a sulphuret of iron with a small proportion of 

 copper 5 and the solution, first obtained, is a sulphate of iron 



