MODERN CHEMISTRY. 437 



exemplified ; and to the consummate skill with which such 

 small quantities have been estimated, we owe some of the 

 most striking discoveries in physiology, agriculture, and the 

 arts of life. 



We have cause indeed to presume, that whenever a par- 

 ticular element is generally present in a compound, and in 

 definite proportion to the other ingredients, such element is 

 essential to its nature, however small the proportion may be. 

 This principle has been constantly confirmed as chemical 

 knowledge advanced ; and it becomes now the expression of 

 phenomena, which may well astonish those not familiar with 

 the subject. It is exemplified by the carbonic acid present 

 in the atmosphere, in a proportion not exceeding J-g-^th part 

 of its weight ; and presumably also by the iodine, bromine, 

 and lithium, in the waters of the sea, though here, as we have 

 seen, the proportion is yet infinitely smaller. The iron exist- 

 ing in a portion of the blood the phosphorus found in the 

 medullary substance of the brain and nerves the fluoric acid 

 in bones the sulphur in albumen, fibrin, and certain other 

 animal matters and the silica, sulphur, phosphorus, and 

 various metallic oxides or alkalies, found in different vegetable 

 substances are a few among the many examples which 

 organic chemistry furnishes of the influence of minute quan- 

 tities in composition. They are relations of deep interest to 

 us, as wonderful and exquisite provisions of Providence for the 

 purposes of life, and for the mutual dependence of the several 

 parts of creation. What they present in natural combina- 

 tions has its counterpart in the artificial chemical union of 

 different substances, where we still find under various forms 

 this marvellous influence of small quantities,* pervading and 

 changing the sensible properties of large masses or volumes 

 of matter. We can destroy the ductility of gold by exposing 

 it, when melted, to the mere fumes of antimony. We can 

 variously change the physical properties of other metals by 



