88 CONSTRUCTION AND MANAGEMENT or SMALL GASWORKS, 



on the market. Some oxides are apt to heat up and fire if 

 allowed to remain in a heap or thick layer, and large lumps, 

 if present, facilitate the action, by rendering the heap open 

 and more pervious to the contact of air. If the oxide fires 

 to any extent, it suffers a serious and permanent injury, so 

 far as gas purifying properties are concerned, and it should 

 specially be observed that a temperature high enough to 

 fuse the sulphur is objectionable. Some varieties of 

 sulphur fuse at a very low temperature. So long as there is 

 no fusing or priming, a moderate heating is an advantage, 

 and if the oxide contains a large proportion of clay or sand, 

 it may be an advantage to let it stand in the heap, and heat 

 up slightly. There is a similarity between the slaking of 

 lime and the revivifying of oxide, as in both cases the 

 material gets warm. The freer the exposure to air 

 the better, but there should not be a cutting draught on any 

 one part of the heap, as that is a common cause of firing. 

 The spent comes round quicker in the open than in a shed, 

 and a gentle shower of rain does not hurt it. But in most 

 climates a roof is necessary, as a protection against heavy 

 rain. The sides of the revivifying shed should be as open 

 as possible, and a few screens, perhaps 10 feet by 6 feet, of 

 light boarding are a convenience as a protection against 

 driving rain or wind. The roof should not be a close one, 

 but provided with ventilation openings. The remarks 

 previously made as to the ventilation of retort houses also 

 apply to the revivifying shed. 



