FUEL BY-PRODUCTS 59 



is one of moderate temperature. With high temperatures 

 and strong draughts the ammonia compounds are carried 

 up the chimney, whilst with lower temperatures they are 

 deposited near the source. It is obvious, therefore, that the 

 point where the major part of the ammonia condenses will 

 vary from hour to hour in the same grate. 



Soot, when used as a fertilizer, is a substance of consider- 

 able importance, its value being often quite as much due 

 to physical and poisonous properties as to its fertilizing 

 elements. The dark colour of the soot makes it a very 

 effective absorbent of the sun's rays, so that for garden 

 work it is very valuable, as it raises the temperature of the 

 soil 2 or 3 above that of land which has not been darkened 

 in colour ; there is no corresponding loss of heat at night 

 by radiation from these darkened soils, since a local mist is 

 produced over the surface at night which prevents further 

 loss. Soot makes a very valuable top dressing for wheat, 

 the accruing benefits being very probably due to its nitrogen 

 content. Soot is also specially distasteful to slugs and 

 small snails, and is largely used by gardeners for that reason. 

 As nearly the whole of the nitrogen in the soot is present as 

 ammonium salts, this fertilizer is a quick-acting one. Soot 

 is very commonly sold by the bushel. The best varieties 

 of soot, as produced in the domestic grate, are much lighter 

 than the poorer varieties from the factory chimney. There 

 is, in fact, a fairly close relationship between the percentage 

 of nitrogen and the weight in pounds per bushel. On the 

 average, a soot containing about i % of nitrogen weighs 

 40 Ibs. to the bushel, with 2 % of nitrogen about 33 Ibs. per 

 bushel, with 4 % of nitrogen 24 Ibs. per bushel, and with 7 % 

 of nitrogen 15 Ibs. per bushel. 



REFERENCES TO SECTION II. 



Cottrell, " Problems in Smoke, Fuel and Dust Abatement," An. Rep, 

 Smithsonian Inst., 1913, 653. 



Evans, " Aspects of the Low Temperature Carbonization of Coal," 

 Journ. Soc. Chem. Ind., 1918, p. 212 T. 



Short, " The Carbonization of Durham Coking Coal and the Distribu- 

 tion of Nitrogen and Sulphur," Journ. Soc. Chem. Ind., 1907, p. 581. 



