96 PROCESS FOR DETECTION OF ADULTERATIONS. 
the pungent taste of the resulting solution, as well as by the 
lighter colour of the mustard-husk, as compared with that of 
the rape.* The process of analysis, however, that I was at 
last induced to resort to is, undoubtedly, much more con- 
clusive, and will henceforth, I am satisfied, be invariably 
employed by agricultural chemists in investigations of this 
nature. It consists in treating the cake, previously broken 
up into small pieces, with repeated portions of boiling water, 
and squeezing the insoluble remainder in a linen cloth, so as 
to obtain the husk of the seed in a separate state, and then 
to act upon the latter with hot dilute nitric acid, and examine 
its structure under a microscope. By means of the nitric 
acid, the starch, grains, &c., are dissolved, and the husks 
themselves are rendered so transparent, as to readily admit 
of their structure, and the form of their constituent cells 
being observed. The form of these cells in the husks of the 
various oleaginous seeds is so essentially different, that a 
simple examination by this process will immediately con- 
vince us, that a better means of detecting the adulteration of 
the oil cakes could not be devised. Thus, for example, the 
cells in the mustard-husk are very small, whilst those of the 
rape and linseed-husk are considerably larger, and differ 
from them in shape. The mustard-husk has, moreover, 
so to speak, a hexagonal network of thicker tissue which 
is very characteristic, and is not observed in either of the 
others. 
A somewhat similar method of analysis will also enable the 
chemist to detect the adulteration of wheaten flour, with the 
flour of the leguminosa (beans, peas, & c.) and buck-wheat; 
and that of certain cereals, as barley, oats, rye, and Indian 
corn; as well as the adulteration of bread with mashed 
potatoes. M. Donny has shown that the cellular matter of 
leguminous flour, is very different in its microscopic cha- 
racters to that of wheaten flour, and of the cereals generally. 
The mode, therefore, in which I proceed to separate this 
cellular matter for examination, is to heat about two or three 
hundred grains of the suspected flour or bread, in a small 
^evaporating dish, with a sufficient quantity of dilute nitric 
acid, composed of about one part of ordinary nitric acid with 
six or seven parts of water, until the whole of the starchy 
and glutinous matters are dissolved ; and then to collect the 
yellow cellular particles, which float as a scum on the surface 
of the acid liquid, and submit them to examination, by a 
* See Professor Johnston’s c Instructions for the Analysis of Soils/ &c., 
p. 90. 
