656 
. Analyses of Ashes of Plants. 
we desire now more distinctly to point out the connection which 
exists between it and the value of different specimens of wheat. 
The specific gravity of wheat, we have said, is its true weight, 
Avith which no peculiarity of shape or size of the grains, no damp- 
ness or roughness of the skin, can interfere. Every farmer knows 
that the weight per bushel is most materially influenced by these 
circumstances, and, making allowances for them, is accustomed to 
consider it as a sure criterion of the value of the sample. It is 
known that the strength of flour and its fitness for making good 
bread is due to the gluten contained in it, and corresponds to a con- 
siderable extent with the weight per bushel — the greater the 
weight per bushel the better the flour. But setting aside the acci- 
dental differences of skin which are the result of threshing in damp 
weather, &c., and taking two wheats as nearly alike as possible in 
this respect, the question to decide will be — Is the wheat of most 
pounds to the bushel necessarily tlie heavier? — in other words. 
Does it contain more gluten? — Is it the best for the baker, the most 
nutritive for the consumer ? We are prepared to show that it is not. 
The subject of specific gravity is rather difficult for parties un- 
accustomed to these matters to conceive, and it is particularly so 
in the case of a body consisting of individual grains like wheat. 
It is easy to understand and express the relation in weight ex- 
isting between a cubic foot of water, of marble, and of iron. We 
should find, if we weighed this quantity of the three substances 
named, that the marble would weigh nearly three times and the 
iron seven times as much as the water. But the weight of a given 
bulk of any substance can only be compared with that of another 
(for the sake of determining the relative weights of the matter 
composing them) when there are no interstices or hollows in it. 
Wood is considered to be lighter than water because it floats upon 
it, but this is due to the air contained in its pores. Wood is really 
much heavier than water, and in consequence sawdust will be 
found very shortly to fall to the bottom of a vessel of water into 
which it is thrown. 
Now this reasoning applies equally to wheat. Were the grains 
of wheat solid bodies of large dimensions, so that they could 
readily be measured by the rule, or indeed were the grains all 
exactly of one size, the relative weight of two specimens could 
easily be made out, but this is not the case ; a bushel of wheat is 
in the same predicament as a mass of wood ; we cannot tell the 
true weight of the matter composing one or the other by weighing 
a certain measure of it, because the intei-stices between the grains 
of two specimens of wheat may differ in the same way as the pores 
or hollows of two kinds of wood. The weight, then, of any mea- 
sure of two different grains will not correspond with their relative 
weight, supposing them solid, and therefore the weight per bushel 
may differ, the real weight remaining the same, or vice versd. 
