13 INTRODUCTORY [chap. 



skin, fish, malt dust, and meal of decayed corn, so that 

 a knowledge of the value of these materials must have 

 been widespread. 



William Kllis, a Hertfordshire farmer who wrote in 

 1732, enumerates a long list of "hand manures," the 

 use of which he regarded as characteristic of Hertford- 

 shire farming in his day. These include soot, wood 

 ashes, woollen rags, horn shavings, hoofs, hair, coney 

 clippings, oil cake, and malt dust ; and the regular part 

 they evidently played in the farming of that district 

 show that they must have been known and used for a 

 long time previous to Ellis's writings. Throughout the 

 eighteenth century we hear of the same materials, and 

 also of bones, which Kllis does not mention, though 

 their value is staled by several of the seventeenth 

 century writers. Early in the nineteenth century we 

 begin to hear of guano from Peru, though the first 

 importation did not take place until 184a 



The importation of nitrate of soda from Chile had 

 begun a year or two before ; its value as manure was 

 for a time in doubt, though as early as 1669 Sir Kenelm 

 Digby had recounted an experiment to show how much 

 barley plants were benefited by watering with a weak 

 solution of nitre, and Evelyn in 1675 ^^^ written: "I 

 firmly believe that were saltpetre to be obtained in 

 plenty, we should need but few other composts to 

 meliorate our ground." 



The employment of ammoniacal salts seems to have 

 begun entirely upon theoretical grounds ; de Saussure 

 had attributed the nitrogen of vegetation to the 

 ammonia in the atmosphere, and in this he was 

 followed by Liebig; fortunately, about the same time, 

 the manufacture of coal-gas gave to the world a cheap 

 source of ammonium salts. Lawes had already been 

 trying them before Liebig's paper of 1840, and when 



