236 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
THE USES OF LIME IN AGRICULTURE AND 
HORTICULTURE. 
By H. E. P. Hodsoll, F.C.S., M.S.E.A.C. 
[Read July 18, 1916; Mr. W. Hales, A.L.S., in the Chair.] 
At the present time, when the need of obtaining the utmost from the 
soil of our gardens as well as our fields is imperative in the national 
interest, it is particularly important that we should not forget the 
valuable assistance that lime can render us in attaining this object. 
Liming is the cheapest of all horticultural " improvements/' both from 
the point of view of cost of application and from the measure of results 
obtained. The importance of the part played by lime in the soil is 
far greater than is generally realized ; without it the land is sterile ; 
with it, it becomes fertile, because, as we shall see, all the processes of 
plant nutrition depend upon it. 
Origin and Composition.- — First let us examine the origin and com- 
position of lime. What, in its ultimate nature, is lime ? How does it 
#ccur, what is the relation of the various types of lime on the market, 
how are they produced, and what is their chemical composition ? 
These questions are perhaps most easily answered by an examination 
of the chart given below. 
Ca = Calcium — light yellow metal — very reactive — 
does not exist in nature. 
I + O = CaO. 
CaO = Calcium oxide, caustic or burnt lime — very 
reactive, very active base. 
+ H 2 0 = CaH 2 O s . 
CaH 2 0 2 = Calcium hydrate, slaked lime — reactive. 
I + C0 2 = CaCOg + H 2 0. 
CaC0 3 = Calcium carbonate, limestone or chalk. 
Nitrogen Potash Phosphoric Acid 
I i I 
CaC0 3 + H u m u s (by 
J action of bac- 
| teria) 
Ammonium carbonate 
Calcium nitrite 
Calcium nitrate (soluble, 
taken up by plant). 
CaC0 3 + complex com- 
| pounds of silica, 
J potash, and alumina 
Silicates of calcium and 
potash in solution 
Also potash added in 
manures retained. 
CaC0 3 + Phosphates of 
alumina and iron 
Phosphate of calcium, 
also phosphates added 
in manures retained 
as calcium diphos- 
phate (available). 
It will be seen that the basic metal is calcium, and that the 
various forms of lime as we know them commercially are com- 
pounds of calcium. At the head of the chart, therefore, we have 
the metal calcium, which is very reactive and does not exist as 
such in nature — there is no such thing as free calcium. It can, 
of course, be isolated in the laboratory, but immediately it comes 
