On the Food of Plants. 
545 
arises from the mere increase in the quantity of grain when the 
salt is used as a top-dressing- for wheat. 
It is well known that the proportion of gluten in flour varies 
very much in different samples of the same grain, according to 
the circumstances under which it has been grown, and especially 
the kind of manure used. The experiments of Herbstocd and 
Boussingault sufficiently prove this ; so that by the use of a richly- 
azotized manure, such as urine or putrid blood, the proportion of 
gluten, the most valuable part of the flour, may be prodigiously 
increased. Now the same thing is, according to Mr. Hyett, 
effected by the use of nitrate of soda. In the case by him described 
the gluten was raised from 19 to 23 '25 per cent. — a most im- 
portant difference. 
I am indebted to the kindness of friends for the means of re- 
peating this experiment. Among the analyses of the ashes of 
wheat before given will be found those of an experimental crop 
raised in Berkshire,* in the same field, and as nearly as possible 
under similar circumstances, except that one-half was treated with 
nitrate of soda, and the other not. The experiment was de- 
cidedly a successful one, the produce being considerably in- 
creased. 
It will be seen from the analysis referred to that no important 
alteration of the inorganic constituents of the crop occuri'ed under 
the influence of the nitrate ; a little more soda than common 
seemed to have been introduced into the straw, but nothing more. 
The value of the manure is thus due to the nitric acid. 
In the Appendix will be found a description of a mode of 
determining the proportion of gluten in meal of different kinds, 
which promises to give results infinitely more to be relied on 
than those got by the old process of mechanical separation. This 
consists in ascertaining the per-centage of nitrogen present by the 
aid of the ultimate analysis, and then referring the nitrogen to 
gluten, on the supposition that that substance contains very nearly 
15*5 per cent, of azote — a supposition which the analyses of Dr. 
Bence Jones and others in Liebig's laboratory have shown to be 
not far from the mark. In this manner the following results 
were obtained : — 
1. Wheat grown in Battersea Fields last year, well dried in 
the air : a portion was carefully ground in a mortar, and the 
bran separated by sifting through fine muslin. It contained in 
500 grains : — 
* By T. H. Smith, Esq., Kintbury, Berks, to whom I take this opportu- 
nity ot returning thanlcs ; and also to Charles Alderman, Esq., of Kintbury, 
I'or his many acts of polite attention. 
2 N 2 
