20 OF THE FREE DIATOMACEJE. 



sand are mixed with the captured Diatomaceae, 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 Diatomaceaa 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 Diatomaceas 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 



