202 Fertiliser's [pt. hi 



Soot and flue dusts. Three types of soot and flue dusts 

 are available, only two of which, however, possess 

 manurial value. 



1. Household soot, which may contain anything 

 from 2-5 to 11 per cent, of nitrogen (equivalent to 3 to 

 13 per cent, of ammonia); the lower values are given 

 by mixed samples from dwelling houses, and the higher 

 ones from the light fluffy soot, obtainable from sitting- 

 room or kitchen chimneys ; a usual amount may be put 

 at about 4 per cent. As soot is purchased by the bushel 

 it is moie useful to know the quantity of nitrogen per 

 bushel; this is much less variable than the figures for 

 the percentage composition, because the rich soot is 

 very bulky and the poor soot is more dense. Analyses 

 at Cambridge showed that as a rule 1 bushel of soot 

 contains 1 lb. of nitrogen (mainly as sulphate of am- 

 monia) normally worth about Id. (p. 136). It contains 

 some substance disagreeable to slugs and other pests, 

 and it improves the physical conditions in the soil 

 partly by ameliorating the texture and partly by the 

 warming effect of its black colour. It is applied at the 

 rate of 20-30 bushels per acre as a spring dressing for 

 wheat, supplying both the nitrogen and the warmth 

 that is then needed ; and it is also used for hops in Kent, 

 quantities being sent for the purpose from Manchester 

 and other northern cities^. 



2. Blast furnace flue dust. This is quite a different sub- 

 stance from the foregoing, and owes its value not to nitro- 

 gen but to the potash which has been volatilised from the 

 coal, ore andflux by theintense heat of the furnace (p. 154). 



^ Knccht has extracted a number of interesting compounds from 

 Manchester soot, including a paraffin C27H5g that is also present in 

 beeswax. Proc. Manch. Lit. and Phil. Sot., 1905, p. 49. 



