152 Preparation of Charcoal. 



607. By the Dromart Process a kiln is constructed of cast-iron 

 plates that form the floor and sides, and may be set up and taken 

 down from time to time as it becomes desirable to change the site. 

 Beneath the iron floor there are flues leading to equi-distant points 

 in the bottom, and a fire is kindled externally for supplying in part 

 the heat required by the process. There are air-holes around the 

 side and a chimney at the top, all of which may be opened or closed 

 at will. The wood is set up endwise, and fills the entire space. In 

 this, as in all other kilns, the volatile products may be saved. 



608. The Moreau Process proposes to secure carbonization in sheet- 

 iron receivers of cylindrical or prismatic form, and capable of hold- 

 ing a cord or two each. They are filled at the top through an open- 

 ing that may be closely sealed, and the air is admitted through 

 perforated tubes from below. These receivers are so arranged that 

 several may be attended by the same men simultaneously, some 

 being filled or emptied while the others are at work. They have 

 no bottom, and are speedily emptied by being turned over on their 

 side. It is claimed that they afford 41 to 43 per cent in volume, 

 and 30 in weight. 



609. Charcoal is an ingredient in gunpowder, and the best is 

 made from the alder buckthorn {Rhamnvs frangvla) , although the 

 common alder, willow, soft maple, hornbeam, basswood, and poplar 

 are used. It is best prepared in iron retorts, in which the heat is 

 applied externally, and the wood should be peeled, to avoid acci- 

 dents from the ignition by sparks from sand in the bark in manu- 

 feeture. 



610. The percentage of ash in woods, as a rule, decreases as well 

 in the bark as the wood, from below upwards, being more in the 

 branches than in the trunk, and most in the twigs and leaves. In 

 coniferous trees, the alkalies, magnesia, phosphoric acid, and sul- 

 phuric acid in various combinations, occur most in the needles, and 

 lime, iron, and manganese in the bark, and small branches. 



611. By far the most ashes are contained in the cambium and 

 bark bundles, and more in the sap-wood generally than in the heart- 

 wood. As the cellular system ceases to be active, it appears to give 

 up its alkali and phosphoric acid to the use of the younger forma- 

 tions, and thus in the life-process the same atoms may be used over 

 and again in the same tree. 



612. It follows, from this, that the tree when young requires rela- 

 tively more food than when old, and that nurseries exhaust the soil 



