42, Lester Reed on 
Starch is to be regarded as a definite chemical substance, 
having an existence and identity independently of its granular 
structure; nor is the granule necessarily composed entirely of 
one substance. It is a small structure built up chiefly of starch, 
on a plan varying with the nature of the plant from which it is 
derived. Starch is a substance allied to sugar and to cellulose, 
having, in common with these, the peculiarity that it consists of 
carbon united to hydrogen and oxygen, the two last being in the 
exact proportions in which they exist in water; so that if we 
remove the elements of water from starch, sugar, or cellulose, a 
black mass of carbon remains, and all these substances are there- 
fore charred by strong sulphuric acid (which has a great attraction 
for water) for this reason. 
Occasionally a chemist requires to ascertain whether a particular 
fibrous structure is cellulose or not, and, although a mere exami- 
nation of structure with the microscope may be sufficient to dis- 
tinguish, for example, fibres of scraped leather from those of 
cotton or paper (cellulose), it is convenient to apply, as a con- 
firmation, a colour-test in this case also. 
Iodine, however, under ordinary circumstances will not give 
any such blue colour with cellulose, as it will with starch, but in 
the presence of chloride of zinc it will do so. So that if we mix 
together fibres of cotton and leather, and treat them dry on a 
slide with the iodine and chloride of zine solution, and then 
place the cover-glass over, we see all the cotton fibres blue, 
while those of leather are colourless. 
Another colour reaction may be made use of to detect ferru- 
ginous particles in drinking-water. We allow a drop of the 
water, containing some of the particles to be examined, to dry 
on a slide, warming it, until it does so, over a small flame, then, 
having placed on a cover-glass a drop of mixed solution of ferro- 
cyanide of potassium and hydrochloric acid, we invert this on to 
the dried residue of the drop, and upon examining under the 
microscope shall probably see one or more bright blue particles; 
these are due to the formation of prussian blue, by the action of 
these reagents upon the iron-containing particles originally sus- 
pended in the water that was to be examined. 
Perhaps one of the most common uses of the microscope for 
the detection of adulteration is in the case of coffee wherein we 
have to search for chicory. In this case I have not yet been able 
to find any chemical reagent which will give satisfactorily a 
characteristic effect visible in the microscope, and it seems to be 
necessary to rely, as regards the microscopical examination, upon 
differences of structure only. The presence of chicory, if that 
substance appears to be present, must of course be confirmed by 
independent chemical tests. Chicory contains sugar and sodium, 
neither of which are present to any extent in normal coffee, and 
