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starch will sink to the bottom and form a white layer beneath 
the cocoa. On warming the water, the fat will of course 
float on the top, and the sugar will be dissolved. The sugar 
crystals and fat are also shown by redrying the solution on 
a glass slide. 
Sugar is mixed with inferior kinds of the same article, 
but not (as popularly believed) with sand ; the chief impu- 
rities in raw sugar are cane fibre, accidental dirt, and the 
sugar mite or acarus. The latter exists in most raw sugars 
(out of 72 samples, 69 contained mites); but more abund- 
antly in the moderately brown kinds than in the darker. 
The insect is barely visible to the naked eye. To obtain 
specimens, the sample should be dissolved in tepid water and 
well stirred, then allowed to stand a few minutes, and the 
acari will be found as minute particles floating on the top. 
The process of refining entirely removes these and the other 
impurities named. 
Mustard is invariably adulterated with flour, which forms 
one half or three fourths of the article as usually sold. It 
may be readily detected by the microscope, mustard itself 
containing no starch whatever. Turmeric is often added to 
bring up the colour, after this wholesale admixture, and 
cayenne to give it strength. 
Pepper may now be obtained pure of respectable dealers ; 
but as regards the cheaper kinds, and in poor neighbour- 
hoods, it is largely adulterated with meal or starch, gypsum, 
and dirt of any kind, to give bulk and weight. The starchy 
substances may be detected by the microscope, the earthy 
ones will be left as ash after burning, and their character 
may be ascertained by the polariscope. The particles of 
pepper itself are easily recognized by the characteristic stel- 
late cells in the outer skin, and the hard angular ones 
of the inner part of the seed. 
