1 June, 1900.] QUEENSLAND AGRICULTURAL JOURNAL. 447 
_ Perhaps, before proceeding further, a short account of the chemistry of 
lime might not be out of place. 
Lime is a salt or compound of a metal calcium, the compounds of which 
occur very widely distributed. One of the principal of these is “limestone,” 
Which is a more or less pure form of calcium carbonate (a compound of calcium 
With carbonic acid). 
eee forms of calcium carbonate are shells, corals, and earths known as 
Tharls. 
Other compounds of calcium used for agricultural purposes are “ gypsum” 
(a compound of calcium and sulphuric acid) and “ gas-lime,” which’ is lime 
Which has been used in the gasworks to remove sulphurous and other impurities, 
and consists essentially of a mixture of slaked lime, calcium carbonate, and 
calcium sulphate. 
_ When limestone is heated, it parts with a gas carbonic anhydride, and quick- 
lime (calcium oxide) is formed. his process is carried out on a large scale in 
kilns, where the heat from burning wood is used to effect the reduction of the 
Imestone to quicklime. 
Quicklime has a great affinity or liking for water, and forms with it calcium 
_ hydrate or slaked lime. This action is so violent that great heat is produced. 
; Slaked lime has the power of combining, with the gas, carbonic anhydride, 
Which is always present in the air, forming calcium carbonate. 
The changes of quicklime to slaked lime and of slaked lime to carbonate 
will occur in the soil when lime is used. 
Opinion differs considerably as to the class of lands most benefited by the 
use of lime, and also as to its application ; German writers urging its application 
to heavy lands, while French writers recommend its use on open light soils. 
) In many localities the use of lime has been proportionate to the facility 
| With which it could be obtained, and as examples of the very great benefits 
derived from the use of lime might be cited the soils of the French province of 
imousin, and, what is perhaps better known, the soils of Hawaii as treated by 
Dr. Maxwell. In the application of lime to soils, one well-known authority 
- Tecommends that lime be harrowed in and not ploughed, while Professor Storer 
Says that theoretically lime had better be ploughed in than harrowed. The 
general practice is, I think, to harrow in, since the fact that lime will sink 
through the cultivatable soil into the subsoil, or go off in the drainage water, 
as been noted by many. 
As to the quantity of lime to be applied, opinion and customs differ, but 
eavy dressings, except in particular cases, are now discouraged; the idea 
being to apply a lighter dressing oftener than a heavy one at much greater 
Intervals. 
_ _ In England, the old practice was to apply 4 to 8 tons lime per acre, though 
mm Derbyshire as much as 16 tons has been applied. This application was made 
about once in sixteen years, but the general practice seems now to be an 
application of not more than 1 or 2 tons per acre every six years. 
_ Instances have been recorded where the practice of applying 6 to 8 cwt. 
lime per acre, when the land had been prepared for seed, and before sowing the 
_ $rain, has given most satisfactory results. 
From experiments made by Scott and Morton, the application of lime is — 
tecommended of from ‘05 to *50 (according to circumstances) per cent. of 
Weight of the cultivated soil. Thus on an average soil cultivated to a depth of ' 
0 inches, an application of 1 ton per acre would represent ‘05 per cent., and 
10 tons per acre a dressing of *5 per cent. 
Hilgard recommends that for lime-loying plants the percentage of lime 
Should be not less than ‘10 if soil be light sandy; 25 if soil be clay loam; 
| 50 if heavy clay, and may advantageously rise to | or even 2 per cent. Beyond 
this last-named amount, it seems in no case to act more favourably than a less’ 
‘mount, unless it be mechanically. 
West Indian authorities state that good cane soil should contain “4.to ‘9 per 
| Cent. of lime. : 
