82 FORMATION OF POTASH. 



The nitre beds in France are composed of 

 nitrous earth taken from farm-yards, stables, 

 privies, &c,, of street sweepings, mild calca- 

 reous earth (chalky soil) or old mortar, plaster, 

 or even of the sweepings of roads paved with 

 limestone, of animal matter, such as night 

 soil, blood, refuse from the skinner's or tan- 

 ner's yards, offal, &c., and of vegetable matter, 

 such as straw, stable litter, saw-dust, spent 

 tanner's bark, leaves, &c., these are all mixed 

 together in somewhat casual proportions, care 

 being taken that a sufficient quantity of calca'- 

 reous matter is present, the heap is then made 

 up into a long bed, protected from the weather 

 by a suitable roof, and is then duly moistened 

 with putrid water or urine. In this way a 

 large'quantity of nitrate is every year produced 

 by lixiviation, but great part of it is now in 

 the state of nitrate of lime, and it requires the 

 addition of a quantity of wood ashes to supply 

 the necessary potash, and convert the result 

 into a pure nitrate of potash, or the wood ashes 

 might be added at the time of forming the 

 bed, using only a small proportion of the cal- 

 careous earth, and this would at once combine 

 and produce in the soil the desired nitrate of 

 potash. 



^ . The proportion of nitre afforded by these 

 beds is about 12 ozs. for every 100 lbs. of 

 material employed, but the proportion varies 

 both above and below this quantity, accord- 

 ing to the value of the materials employed to 

 form it, and the care subsequently taken in 

 managing it. 



