EXPERIMENT STATION. 61 



The compounds actually existing in the Canaan lime, 796, are 

 almost certainly, both in kind and quantity, as given helow. The 

 state of combination of the ingredients of 797 cannot be so posi- 

 tively ascertained from the analysis. The statement below is 

 probably correct except that the silica is combined with the iron 

 and a small part of the lime (perhaps also with a little magnesia 

 and alumina). The quantities of lime, etc., thai thus chemically 

 unite to silica in the burning of impure limestones, such as yield 

 797, depend upon the temperature to which the rock is subjected 

 in the kiln. 



Calcium hydrate (slacked lime), 79.61 12.62 



Calcium carbonate (carbonate of lime).. 17.63 7.91 



Magnesium hydrate, - -- 98 



Magnesium oxide (magnesia), — 31.59 



Calcium oxide (lime) ' - 32.80 



Oxide of iron and alumina, - .20 3.61 



Matters insoluble in acid, - 28 5.78 



Silica (combined with lime andiron as silicates,)- 5.56 



Moisture, uudetermiued matters and loss, 1.30 .13 



100.00 100.00 



The effect of much silicates (glass- or slag-like compounds formed 

 by strongly heating together silica and lime or iron) in a lime is 

 to "bind" the lime and retard slacking. The effect of magnesia, 

 especially in large proportion, is also to retard or prevent slacking 

 and to diminish the caustic or corroding quality of the lime. 



Sample 797 is stated not to have heated when drenched with 

 water, but after standing three weeks it crumbled without killing 

 the grass on which it was heaped. 



The question of the comparative value of the two samples is an 

 important one. 797 was bought for application upon tobacco- 

 land. The value of lime applied to land is of two sorts. It may 

 be of service by its caustic or alkaline character in virtue of which 

 it, for example, provokes decomposition of the inert nitrogen- 

 compounds of the soil and thus acts indirectly as a supply of 

 nitrogen. For this use 796 is much superior to 797- The other 

 mode of action of fertilizer-lime lies in its direct supply of plant- 

 food. On a soil destitute of magnesia, 797 w^ould be better than 

 796, but magnesia is commonly abundant enough in our soils, 

 and while an occasional application of a magnesia fertilizer may 

 be advantageous we may conclude that, generally speaking, a 

 nearly pure lime is preferable to one containing a large proportion 

 of magnesia. 



