EMPYREUMATIC OILS. 237 



The earth is then dug out a spade deep, sloping 

 from the centre to the circumference, and is thrown 

 up forming a bank round the circle. A straight 

 pine, of sufficient length to reach from the centre 

 some way beyond the bank, is split longitudinally 

 and hollowed out. The parts are then put together 

 again and one end is placed in the centre, being so 

 supported on the ground that this end is higher 

 than that which comes without the bank, where a 

 hole is dug into the ground, into which the tar flows 

 from the channel, and whence it is from time to time 

 taken out and barrelled for market without any 

 farther preparation. 



After the kiln is marked out, the wood, being split 

 up in small billets, is packed as close as possible 

 with the inward ends sloping towards the middle, 

 which is filled up with smaller pieces consisting of 

 the knots of the trees, these yielding more tar than 

 any other part of the wood. The kiln is built in such 

 a manner, that at twelve or fourteen feet high it will 

 overhang two or three feet, and appear quite com- 

 pact and solid. After the whole of the wood is 

 piled a number of small logs are placed round it, then 

 a layer of turf, and so on alternately throughout the 

 whole height ; the top is then covered over with two 

 or three layers of turf. After the whole is thus ar- 

 ranged, a turf is taken out in ten or twelve different 

 places round the top, at each of which parts fire is 

 applied, and the pile then burns downwards, till the 

 whole of the tar is distilled from it. If combustion 

 proceeds too rapidly, some of the holes must be 

 stopped up, if too slowly, others should be opened ; 

 practice enables a tar-burner to judge with tolerable 

 accuracy as to the best measures to be pursued in 

 this respect. Six or eight days are generally required 

 to complete the burning of a tar-kiln of the dimen- 

 sions here described. 



