TuLKj on Cleaning and Preparing Diatoms. 7 
are, which,, in proportion to their weight, are of small super- 
ficial area; the consequence is, if the whirling motion is 
gradually reduced in force until it is altogether discontinued, 
it will be found that the mass has arranged itself about the 
centre of the basin, the siliceous particles being below, and 
the diatoms lying as a stratum upon them. The latter may 
now easily be separated. 
Again the slight whirling motion is given to the vessel, when 
immediately a cloud of diatoms is seen to rise up from the 
mass into the centre of the water. Into this cloud the capil- 
lary end of a small dipping-tube, three and a half inches long 
and a quarter inch diameter inside, is inserted, at an inclined 
angle, when at once a portion of the pure diatoms will enter 
it, and from this they may be blown into a small bottle. By 
successively performing this operation a very large proportion 
of the diatoms may be obtained in a pure state, and fit for 
mounting. However, there are certain heavy, compact forms, 
which will not readily rise in the whirling process, such, for 
example, as Amphitetras antediluviana, Triceratium Favus, 
Biddulphia turgida, &c., &c., which will be found at the 
bottom of the vessel along with the silica. These may be 
advantageously picked out with a fine needle under a simple 
microscope. 
By a little practice and dexterity in the whirling process, 
so as to produce a less or greater amount of motion of the 
water, the lighter forms may be collected separate from those 
more dense, for the former will rise on a very gentle action 
being given, whilst the latter will require rather more motion 
to stir them. 
The forms thus collected may then be washed in the small 
bottle two or three times with distilled water, when they 
will be in a satisfactory state for mounting. 
It is requisite so to apportion the water in the bottle to 
the quantity of forms, as that when the latter are laid on the 
cover they appear to be neitlier too abundant nor too scant. 
The slide and the cover about to be used should be made 
scrupulously clean, and this is best done by placing on them 
a small quantity of a solution of Ward^s washing powder 
(a packet of which can be procured at any grocer's shop for 
one penny, and which will be found most useful for removing 
balsam or grease from slides), well rubbing them with the 
finger, and drying them with a clean cloth. Any filaments 
from the cloth should be picked off with a needle under the 
microscope. 
The cover should then be made to adhere to a slide, by 
