Monthly Microscopical | 
Journal, Dec. 1, 1870. _ 
On Selecting and Mounting Diatoms. 311 
finishing coat of asphalte or other varnish may be added, and thus 
all danger of damp or of crystals is avoided. 
Captain Haig gave me two other most useful hints, which he 
has most kindly allowed me to mention. Of course all diatoms 
should be mounted on the cover. ‘To secure the correct centering 
of them, he forms on a glass slip, by means of the turn-table, a ring 
of gold-size 2ths of an inch in diameter, the size of his covering 
glass, and within this a very minute one exactly in the centre. 
This is hardened by heat, as his cells are. On the outer ring, at 
equal distances, are placed three little bits of beeswax. The cover- 
ing glass, on which it is intended to arrange the diatoms, is placed 
on this general mounting slip, and slightly pressed on the wax. 
Instead of distilled water, he places on the cover a very slight 
smear of glycerine, into which previously, as in the case of the 
water, a drop of gum may have been added. Into this the diatoms 
are dropped, and may then be pushed within the inner ring, and 
their perfect arrangement and centering are secured. The advan- 
tage of the glycerine over the water is that it is a greater solvent 
for freeing the diatoms from any extraneous dirt, and that it will 
remain moist for any length of time. When the arrangement is 
completed, the covering glass is gently pushed off the three pieces 
of wax, and transferred from the slide to the hot plate, when in a 
few minutes the glycerine is evaporated. Put on another slide 
under the microscope, a drop of benzole is placed on the diatoms, 
and whilst they are being permeated by it, and all air displaced, a 
little balsam is dropped into the prepared cell, when the cover is 
seized by the forceps, reversed, and placed carefully on it, and the 
mounting is completed in less time than it has taken to tell the 
process. 
I must state, however, that Mr. Tatem, whose slides of diatoms 
are almost absolutely perfect as to cleanliness and neatness of ar- 
rangement, prefers simple distilled water, with of course the neces- 
sary addition of gum, to the glycerine, which he considers messy. 
He uses a finely-pointed sable brush, instead of the badger’s hair, 
both for selecting and arranging; for though, owing to the rapid 
evaporation of the water, the diatoms may become dry and fixed 
before they are exactly in position, a touch of the brush again 
moistens them, when they may be shifted as required. He also 
places his cover with the diatoms on the cell, which has been simply 
filled with chloroform, and then, placmg the balsam at the edge, 
allows it to run in and replace the more volatile medium as it 
evaporates, thereby avoiding all chance of an entangled air-bubble. 
This process, however, must entail a good deal more trouble in 
cleaning off the superfluous balsam; and after mounting many dozens 
of slides after my plan I may fairly assert that I have never once 
been troubled by a persistent air-bubble; whilst a very little ex- 
perience teaches the manipulator the exact quantity of balsam 
