432 The Neglect of Chemistry hy Practical Farmers, 



always show the whole sulphur contained in the specimen ; in 

 some instances the quantity lost during combustion being very 

 considerable. 



Carbonic Acid, — The principal properties of this acid are de- 

 scribed under the head of " Carbon." It is a product of the com- 

 bustion of organic matter, indicating the amount of organic acids 

 that previously existed in the plant, in union with various bases. 

 Some chemists omit this acid altogether in stating the result of 

 their analyses, on account of its being an organic compound, and 

 therefore the reader must not always infer that there is none pre- 

 sent in the ash when a blank occurs under this head. The surest 

 method of discovering whether it is really absent, or merely an 

 omission of the chemist, is, by examining the analyses of those 

 chemists who always give the amount when present. This omis- 

 sion in analyses for practical purposes is greatly to be deplored, 

 as it prevents any correct estimation of the quantity of the various 

 ingredients from being obtained from the amount of ash, the result 

 being above the true quantity. In proportion to the quantity of 

 carbonic acid contained in the ash all the calculations in these 

 tables, where this is the case, are necessarily erroneous to that 

 extent. 



Having now glanced at the composition and peculiar properties 

 of the various substances referred to in these tables, there remain 

 but the two small columns, next to the classification of the plants, 

 to be noticed. The reader will perceive that their heading is not 

 always the same, but the only two that require any remarks are 

 those headed " Proportion per Cent. " and " Specific Gravity." 



Proportion per Cerit. — The numbers given under this head 

 express the relative proportions by weight of the several parts of 

 the plant, as, for instance, the grain, straw, and chaff of wheat. 

 Supposing the whole plant to equal 100, they are the actual mean 

 proportions of the specimens analysed, as found by the chemist. 

 The reader will perceive that in Part 4 of these tables I have not 

 adhered to these proportions in my calculations. My reason for 

 so doing was, not that I doubted the superior accuracy of the 

 chemist's scales when compared with the farmer's, but that I 

 thought it probable that the specimens sent for analysis might not 

 include any light ears, &c., and therefore not be a fair average of 

 the field. 



Specific Gravity. — By this term we mean the ratio of weight to 

 bulk ; the specific gravity of bodies gives the relative weights of 

 equal bulks of those bodies, water being the standard. It is 

 determined by weighing a substance first in air and then in water ; 

 and then dividing its original weight by that of the weight which 

 it lost in water. 



