252 



guano, nitrate of soda, or bone manures. In point of fact, gas-lime 

 exercises a most decidedly beneficial effect upon some soils bat has na 

 effect upon others ; success in its application, therefore depends mainly 

 upon the proper selection of the land upon whicti it is intended to be 

 put. On this point we shall have, presently, to make some special 

 remarks. 



In the first place it will be desirable to inquire a little more closely^ 

 into the 



Chemical Constitution of Gas-lime. 



As already stated, the sulphur compounds and carbonic acid in crude 

 coal gas transform the slaked quicklime ia the purifiers more or less 

 into sulphuret of calcium, a combination of sulphur with calcium, the 

 metallic base of lime, and into carbonate of lime. At the same time 

 some tarry matter, a little ammonia, and other volatile substances pass 

 into the gas-purifiers and are partially retained by the lime in a me- 

 chanical way. Fresh gas-lime has a bad smell, arising mainly from the 

 sulphur compounds contained in it, and should not be put on the land 

 in this condition, for the ameliorating influence of a copious supply of 

 air is required to transform these injurious sulphur compounds into fer- 

 tilising materials, the presence of which, in some respects, renders gas- 

 lime exposed to air for some time superior to quicklime. The oxygen 

 of the atmosphere completely destroys the bad smell of fresh gas-lime, 

 by changing the sulphuret of calcium in it, first into sulphite, and finally 

 into sulphate of lime, or gypsum. There is thus an essential differeuce 

 between Gas-lime newly removed from the purifiers, and after it has 

 been freely exposed to the atmosphere. In a fresh state it contains sul- 

 phur compounds, which give off sulphuretted hydrogen and are injuri- 

 ous to vegetable life ; in the latter condition it contains gypsum, a well- 

 known fertilising substance. The longer this refuse material is kept 

 freely exposed to the air, the more completely these baneful changes are 

 effected, and the more efB.cacious it becomes as a manure. In addition 

 to the constituents already mentioned, Gas-lime contains a variable 

 quantity of water, more or less unaltered quicklime, and all the impuri- 

 ties originally contained in the quicklime employed in the gas-works. 

 In fresh Gas-lime the proportion of water varies usually from 30 to 40 

 per cent. ; in old samples there is much less. The following analysis 

 of a sample of Gas-lime, kept long enough to be used with safety as a 

 manure, will show at a glance its complex character : — 



Composition of Gas-lime (dried at 212° Fahr.) 



Water of combination and a little organic matter . 7.24 

 Oxides of iron and alumina, with traces of phospho- | g 49 



ric acid . . . . j * 



Sulphate of lime (gypsum) . . . 4 . 64 



Sulphite of lime , . * .15.19 



Carbonate of lime . . . . 49 . 40 



Caustic lime . . . .18.23 



Magnesia and alkalies . . .2.53 



Insoluble siliceous matter . . .0.28 



100.00 



