204 
ELEMENTARY CHEMICAL MICROSCOPY 
as starches, flour, meals, spices, etc., powdered sucrose, dextrose, 
lactose or soluble dextrin are most useful as diluents. 
When the mixtures under examination are of a density only 
very slightly greater than water and are insoluble therein, and 
therefore if suspended would subside only after a long period, it 
is possible to weigh out a portion of the mixture, add it to water, 
or better, water and glycerine, in a small graduated flask, fill to 
the mark, shake well and quickly remove one cubic centimeter 
or less, for counting. This method avoids the error arising from 
non-uniform quantities, but is longer and more cumbersome than 
the methods already described. 
To further guard against the rapid subsidence of the particles 
in suspension, gums, dextrin, gelatine or mucilage may be added 
to the glycerine-water mixture; in most cases this will be found 
to be a decided improvement.^ When the removal of fats in 
no way alters the morphology nor the dimensions of the elements 
of the powdered material it will generally be found to be an 
advantage to extract the sample with ether or petroleum ether 
after drying and weighing. The particles of the powder are 
more easily and uniformly “ wetted ” and are therefore more 
readily suspended throughout the liquid and may also be more 
evenly distributed upon the slide. 
In order to obtain greater accuracy than is possible by the 
methods already described Wallis ^ mixes with a known weight 
of the powdered substance, a known weight of Lycopodium; 
suspends the mixture in gum tragacanth-glycerine mixture or 
in the case of fatty powders in oils: the number of characteristic 
elements and the number of Lycopodium spores per field on a 
microscope slide are counted. The method in brief is as follows; 
for details the reader is referred to the original article. 0.2 gram 
of a mixture of known percentage composition is thoroughly 
mixed with o.i gram of Lycopodium and suspended in 20 c.c. 
1 Schneider (Microbiology and Microanalysis of Foods) finds gum acacia most 
useful. The addition of a 3 per cent solution to the glycerine-water (i : r) medium 
is recommended, in the proportion of 15 c.c. of the gum solution to to c.c. of the 
glycerine mixture for a 5 grams sample of the powdered material. 
2 Analyst: 41, (1916), 357. 
