44 Mr. Reed on the Microscope and Food Adulteration. 
supposing oatmeal to be found adulterated with barley-starch, 
and from a preliminary examination the mixture supposed to be 
40 per cent., we proceed as follows :— 
“Pure barley-meal and oatmeal are carefully dried at 100° C., 
and mixed so that the mixture is exactly 40 per cent. A few 
grains of this powder are now rubbed up with glycerine and 
alcohol into a smooth paste, which is then further diluted to a 
certain bulk, a drop taken out with a glass rod, and covered with 
a glass, which is gently pressed down. The number of grains of 
barley- and oat-starch are now counted, and their relative pro- 
portion noted; and an exactly similar process is applied to the 
oatmeal in question. If proper care is taken to repeat the ex- 
periments, the result is a near approximation to the truth.” 
In the case of many starches, however, we should probably. 
meet with the difficulty, that while you may be able readily 
enough to identify and count certain of the granules in view, 
there are many others less characteristic and of sizes varying 
from the average. 
Milk, when observed under the microscope, shows fatty glob- 
ules. The fat-globules are lighter than the liquid in which they 
float, as regards specific gravity, and, consequently, when milk 
is allowed to stand, we have a layer of cream. The larger of 
these globules reach the surface first, and some of the more minute 
never get there. There will therefore be only the smaller globules 
to be seen in skim milk, so that the size of the fat-globules may 
be to some extent an indication of the particular form of adultera- 
tion which consists in the abstraction of cream. Starch granules 
in milk would of course be readily detected by the iodine test. 
Occasionally the microscope is of use in identifying a crystal- 
line precipitate in the ordinary course of qualitative analysis, as 
in the case of the ammonio-phosphate of magnesia, or of iodide 
of lead after solution in hot water and reprecipitation by cooling, 
when beautiful iridescent yellow hexagons of very perfect form 
are seen. 
By the aid of photography it is possible to render permanent 
our microscopical observations, but the great advantage of colour 
is lost; indeed, for the purpose of training one’s powers of ob- 
servation, and of fixing in the memory the appearance of objects, 
I doubt if there is anything much better than to practice one’s 
self in making coloured sketches of them. 
Instances of the use of the microscope in food analysis might 
be multiplied; but perhaps'enough has been said to show that 
the microscope is a very valuable adjunct to chemical work, and 
that there exists a wide field for the devising of simple but charac- 
teristic tests by means of observations with the instrument. 
