APPENDIX A XX XIX 
Carolina, mineral phosphates are found in large quantities, and, in 
Florida, this substance is still more abundant. In Tennessee, also 
extensive deposits exist. 
Another abundant source of phosphoric acid, is a by-product in the 
manufacture of steel. Much of the iron used for this purpose in 
England and Germany contains small quantities of phosphorus, which 
makes the metal brittle and unfit for many purposes. In the process of 
transforming the iron into steel, the metal is heated to a very high tem- 
perature when the phosphorus is volatilised and the vapour passed 
through lime, with which it combines, forming phosphate of lime. For 
many years the slag from the iron furnaces was thought to be of no 
value, but chemical analyses showed that it contained large quantities of 
phosphoric acid in available form. This slag is now ground to a fine 
powder and sold as a fertiliser under the name of “basic slag.” The 
German iron works make about 400,000 tons of this phosphatic fertiliser 
every year, and large quantities are also made in England, Belgium and 
other countries. 
From the-facts submitted it seems evident that, as far as the three 
essential elements of plant food are concerned, it is highly probable that 
there will always be a sufficiency for the needs of mankind, and that the 
waste arising from the cropping of the land may be so far restored as 
to assure permanent fertility. The idea sometimes advanced, that the 
rapid increase in population will after a time out-grow the possibilities 
of the earth’s production, seems to point to a very remote contingency. 
The facility with which large areas of the earth’s surface could be stimu- 
lated to increased productiveness, added to the enormous areas of fertile 
land still in its virgin condition, should be sufficient to quiet any fears 
‘ on that score for a very long time. We know that in some parts of 
Great Britain lands have been cultivated more or less continuously for 
upwards of a thousand years and yet are now probably producing as large 
crops as they ever did. This has been mainly accomplished by the feed- 
ing of stock with the crops grown on the land and applying the manure 
obtained to the soil. In this way, if the return is complete, about 90 
per cent of the important elements of plant food taken by crops from 
the soil can be restored to the land. By supplementing the farm manure 
with occasional applications of artificial fertilisers, good crops may be 
indefinitely maintained. 
The value of animal excreta as a fertilizer has been appreciated by 
the husbandman as far back as records go, but it was not until 1804 
that much light was thrown on the value of the mineral constituents of 
plants, when De Saussure announced his discovery of the significance 
