. Discovery. Science. 122 DISCOVERY organic matter, not to the ash constituents as Liebig had suggested, but to the ash constituents + nitrogen compounds. The First Artificial Manures With characteristic energy Lawes and Gilbert de- veloped this discover}-. There was then (as nearly always) a shortage of farmyard manure on farms, and agriculturists had for generations sought for substi- tutes, but with little success. Lawes and Gilbert saw that the mixture of ash constituents and nitrogen compounds would form an effective and more con- centrated substitute, obtainable in very large quanti- tie
. Discovery. Science. 122 DISCOVERY organic matter, not to the ash constituents as Liebig had suggested, but to the ash constituents + nitrogen compounds. The First Artificial Manures With characteristic energy Lawes and Gilbert de- veloped this discover}-. There was then (as nearly always) a shortage of farmyard manure on farms, and agriculturists had for generations sought for substi- tutes, but with little success. Lawes and Gilbert saw that the mixture of ash constituents and nitrogen compounds would form an effective and more con- centrated substitute, obtainable in very large quanti- ties, and of course independently of farmyard manure. Vast deposits of calcium phosphate were kno«-n, and. Fig. I.—effect of FERTILISERS OX THE GROWTH OF WHE.\T. The left-hand sheaf is the produce of the uamanured plot, the others show the elfects of successive increases in the fertiliser given. large quantities of ammonium sulphate were made in the manufacture of coal gas,while potassium compounds could be obtained without difficulty from wood ashes. Lawes and Gilbert therefore proceeded to extend their experiments with these substances, whUe Lawes set up the first factory for producing superphosphate. Farmers gradually came to recognise the value of these artificial manures, and before long they were using many thousands of tons a year. When the Lawes and Gilbert experiments began the ordinary yield of wheat was about 20 bushels per acre : before twenty years had elapsed it had become 30 bushels per acre, and other crops had advanced in like manner. It cannot, of course, be claimed that the whole cause of the improvement lay in the artificial fertilisers, but this was one of the most important factors. The story of the nitrogen compounds in their role of fertUisers reads almost like a romance. Lawes and Gilbert used ammonium salts obtained as a by-product in the manufacture of coal gas. Large quantities are now made every year ; just before the war the world's production from
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