DIFFERENCES IN THE ASH OF PLANTS. 23 



by burning a common locofoco match : the white 

 smoke which goes off at first before the sulphur ig- 

 nites, is phosphoric acid. Phosphorus is used in the 

 making of these matches, because it is a substance that 

 inflames easily by a little friction. All who have rub- 

 bed them on a wall or board in the dark, have observed 

 that they leave a quite bright, luminous trace, distinctly 

 visible. If the match fails to ignite, the end of it will 

 also appear bright, and the peculiar smell of phos- 

 phorus may be perceived. 



Phosphoric acid does not seem to exist in so large 

 quantity as sulphuric acid, as it does not constitute a 

 principal portion of any of our rocks. It forms a very 

 important part of the bones of animals. 



SECTION II. DIFFERENCES IN THE ASH OF CULTIVATED 

 PLANTS. 



We have now noticed each of the substances that 

 were named as occurring in the inorganic part of 

 plants, and have given such of their more remarkable 

 properties and more common forms of appearance as 

 seemed necessary to their recognition by the practical 

 man. 



It has been already stated, that with one or two 

 occasional exceptions, they are all found in the ash of 

 cultivated plants. Sometimes one and sometimes an- 

 other is absent, but generally we find small quantities 

 of nearly all. It does not follow from this, however, 

 that every plant contains the same quantity of ash. 

 The trunk of a tree, for instance, if deprived of its 

 bark, does not yield more than from one to two pounds 

 of ash in one hundred of wood, while the stalk of grass 

 or straw of grain frequently contains from 6 to 14 lbs. 

 in 100. There are some plants which scarcely con- 

 tain any ash whatever, and others in which it forms a 

 large proportion. This difference exists not only be- 



