ARTIFICIAL FERTILISERS 217 



insoluble in water in its fresh state, hence it must be applied 

 to the soil in the early winter; 2-4 ozs. per square yard 

 can be safely dug in. Sulphate of lime or gypsum is more 

 useful as a cleanser than as a fertiliser. 1 1 can be dug in 

 during the winter or spring at the rate of 6-8 ozs. per 

 square yard. Its use on manure heaps has been described 

 in the last chapter. Calcium superphosphate, usually 

 known by gardeners by the name of " superphosphate," 

 is a powerful phosphatic manure, 20-35 % of which is 

 soluble in cold water. It is not really a chemical compound 

 at all, but a mixture of chemicals. Analysis has shown 

 that it contains several phosphates of lime such as mono- 

 calcium phosphate, di-calcium phosphate, and tri-calcium 

 phosphate, and in addition to these phosphates it contains 

 sulphate of lime and sometimes slaked lime. The mono- 

 calcium phosphate is the soluble ingredient, the others are 

 insoluble, or very sparingly soluble. Superphosphate 

 is best applied in the spring or autumn at the rate of 

 2-3 ozs. per square yard, and dug in. It may be used 

 occasionally in the growing season at the rate of I oz. 

 per square yard and forked in. In solution the best method 

 is to put i oz. into every gallon of water, stir well, allow 

 to settle, and use the clear liquid. One application of this 

 each week during the growing season is usually enough, 

 but when the plants are very strong it may be used oftener. 

 It gives the best results on a light soil, but there must be 

 plenty of ordinary lime in the soil. Used on a sour or humic 

 soil it is very bad, increasing the acidity. No compounds 

 of lime except superphosphate should be applied to chalky 

 or limy soils, little benefit would result. 



Compounds of Iron : The only one I need mention is 

 sulphate of iron, known as " green vitriol." It is a powerful 

 compound, useful for intensifying the colour of flowers 

 in the borders. A watering with a solution containing 

 J oz. per gallon of water is enough. This may be given 

 once a week or once a fortnight during the growing season. 

 Applied to Hydrangeas in pots or in the open ground it 

 will turn the flowers blue 



