LONDON AND SUBURBS. 79 



inner side of the oven there go up two or three flues, 

 korstens-pipor, in which there are dampers, spjall. 

 When the damper or valve is opened, the flame and heat 

 have freedom to ascend through it, and thus the heat 

 under the pan diminishes, and consequently the degree of 

 boiling; but when the spjall is shut, the heat is in- 

 creased. The boiling lasts about five, six, or seven days 

 before the lye becomes so thick that it is fit to make 

 vitriol of, which can be proved by means of a special 

 glass globe with holes in it, which they lay in some of the 

 lye, lut, which they have taken up. By means of this 

 hydrometer it is seen how thick the water or lye, vatnet 

 eller luten, is in this boiling-pan. At last, when it is 

 full-boiled, it is tapped off into three large oblong cisterns 

 of lead which stand a little way from the pan, where it is 

 left to stand and cool, when the Vitriol settles on the 

 bottom and sides of these cisterns. The lye which will not 

 give any more vitriol-crystals is poured back into the. 

 pan ; but the Vitriol that has shot out into crystals is 

 collected. 



In the boiling, it is necessary to be particularly careful 

 that the pan is almost constantly full, which is done by 

 pumping more lye out of the cistern into the pan than is 

 boiled in it, because the pan would otherwise melt. Very 

 much and heavy rain on the outspread Marcasite is in- 

 jurious, because the lye which then filters down is so 

 weak that it is not much stronger than mere water, and 

 consequently it requires a great deal of fire, long boiling, 

 and more labour before the Vitriol is produced from it. 

 The owner said he bought every year £100 to £150 worth 

 of this iron-pyrites or Marcasite. As the channels from 

 the Thames [T. I. p. 468] go right into the works, he 

 can lay boats and small barges close alongside, and un- 

 load pyrites and coal. He did not employ much more 

 than two or three persons in the whole factory. 



