Sir Daniel Hall 119 



was bones. Bones make useful manure because of the 

 phosphorus they contain, but bones lie in the soil a very 

 long time before they rot down and form plant food. An 

 important discovery of the nineteenth century was that 

 of the chemist Liebig, who found that bones when 

 treated with sulphuric acid made a splendid plant food ; 

 an almost greater discovery was that of Henslow, who 

 found that coprolite, a mineral found first in Cambridge- 

 shire, could be used like bones for making superphosphates. 

 Of this one manure the world now makes and uses more 

 than six million tons a year. 



The three foods which plants need most are nitrogen, 

 potash, and phosphorus. Without these foods our gar- 

 dens and fields would be deserts, and we should starve. 

 Formerly the farmers got enough of these substances 

 from the old-fashioned manures, but during the past one 

 hundred and fifty years the population of the world has 

 nearly trebled. In the year 1780 the people of this planet 

 numbered only a little over six hundred million ; to-day 

 it is reckoned that there are more than seventeen hundred 

 million, and if Science had not stepped in to help the 

 farmer these multitudes would not have enough food 

 to eat. 



There are many ways in which the scientist has helped 

 us, but none is more important than his provision of 

 artificial food (fertilizers) for our crops. It was in 

 England that agricultural science had its birth, and 

 Englishmen have done a great deal to increase the 

 world's food-supply. 



Most people have heard or read of the Rothamsted 

 Experimental Farm, the most famous place of its kind in 

 the world. Rothamsted, which is near Harpenden, in 

 Hertfordshire, belonged to John Bennet Lawes, who was 

 born in 1814. He was educated at Eton and Oxford. 

 Experiments in chemistry were his favourite amusements 

 as a boy. In 1834, when only twenty, he took up the 



