20 
OF THE FREE DIATOMACEjE. 
wind are mixed with the captured Diatomacese, the former 
must be got rid of by the process of washing alluded to 
just now. 
There are different arrangements for effecting this ; in 
the simplest, a few wine glasses are all the apparatus needed. 
Empty the contents of a bottle into one of these, and 
shake them well together. Let the glass remain at rest 
for a short time, until the heavier particles have sunk to 
the bottom ; then pour the water slowly and carefully into 
another glass, and the Diatomacese and other light bodies 
will be carried with it. As some of the material might be 
lost by clinging to the outside of the glass, in consequence 
of the slow passage of the water, it is a good plan to smear 
the edge with a little tallow or suet : this will cause the 
water to flow in a steady compact stream. Now let the 
vessel be quite still as before, so as to allow of the heavier 
ingredients once more subsiding, and again decant the 
contents, leaving the residue in the glass. This process 
may be repeated again and again, until the Diatomacea? are 
entirely purified from all admixture of mud or sand. 
Indeed, by the same mode of proceeding, the larger species 
may be effectually separated from the lesser ; because, 
owing to their weight and form, certain kinds are sure to 
reach the bottom more quickly than their lighter com- 
panions. The clearer the water appears to the eye, so 
much the longer must the glass remain at rest, because, in 
consequence of their smaller specific gravity, the lesser 
species take a longer time to sink. Lastly, the separate 
deposits are to be examined under the microscope, and 
their contents filtered and dried. 
The plan recommended by Okeden is rather more 
complicated than this, but is perhaps more effectual in the 
end. The gathering of mud and DiatomacesB is emptied 
into a tall narrow vessel — a champagne glass for instance — 
into which water has been poured to the depth of two 
inches, and is then to be stirred with a glass rod. The 
vessel is left quiet until the more solid particles have 
