THE PAKABOLOIDAL OVHE-QROCND KILST. 211 



over those portions of the kila where carbonization was completed. 

 Hence, the first thing that would be done after closing the flue of 

 the chimney would be to pierce small vent holes, 1 to 2 inches in 

 diameter and about 2 feet apart, all round the kUn a foot or so 

 below the apex. The object of these holes, which could be easily 

 made with a bamboo or sapling pointed with iron, would be to 

 admit the necessary amount of air for carbonizing the wood at the 

 top of the kiln and allow the vapours and other gases of distilla- 

 tion to pass out freely. When the carbonization at this level was 

 complete, which fact would be recognized by the pale blue colour 

 and transparency of the smoke, the holes would be closed and a 

 new line of them opened 1 to 2 feet lower down. In this way the 

 charcoal-burner would gradually effect the carbonization of the 

 entire kiln, the natural spread of the fire-cone being aided and 

 regulated by means of the holes. He would then cover up the 

 kiln as thickly as possible in. order to stop all combustion, and in a 

 few days the kiln would have cooled down enough for the covering 

 to be taken off and the charcoal removed. 



Under actual conditions such extreme uniformity is unattainable, 

 owing to several causes of irregularity, the principal of which are 

 the following : — 



(i). Inevitable defects in the packing of the wood, in conse- 

 quence of which unequal draughts are produced, lead- 

 ing to more rapid carbonization and, therefore, more 

 sinking at some points than at others, 

 (ii). Differences in the amount of moisture contained in dif- 

 ferent pieces of wood, 

 (iii). Difference of density, even when only a single species is 



used. 

 (iv). Movements of the atmosphere, from which the kiln can 



never be effectually screened, 

 (v). Unequal nature of the site. 



(vi). Unavoidable errors of judgment, to which the most skil- 

 ful are liable. 

 To overcome these various causes of irregularity requires no lit- 

 tle skill and experience and unremitting care and watchfulness on 

 the part of the charcoal-burner. To gain his end he must have 

 recourse to one or more of the four following measures, which 

 constitute the whole of his duties at the present stage of his 

 work : — 



I. — Erection of a sceeen onthbwindwaed side of the kiln.— 

 The cheapest form of screen is one of thatch supported against 

 upright posts firmly fixed in the ground. But the first precaution 



