8 TuLKj on Cleaning and Preparing Diatoms, 
first breathing on the latter, and then pressing the cover 
down upon it with a needle-point. 
The bottle containing the forms is now well shaken, and 
the small dipping-tube is immersed into the fluid to such a 
point that the liquid ascends into the tube about half an inch. 
The capillary opening of the tube is then made to touch the 
middle of the cover, when at once the liquid will difluse 
itself over the latter, but will not overflow its edges. It is 
then dried very slowly under a large glass shade, otherwise 
the forms will segregate together, after which it is ready for 
mounting, either dry or in balsam. I will describe how the 
latter operation should be performed. 
A drop of Canada balsam, taken out of the balsam bottle 
on the head of a common pin which has been immersed into 
it, is transferred to the centre of the slide, and the cover, 
one end of which has first been made to rest on the slide, 
gently laid over it, when, by capillary attraction, the balsam 
will diffuse itself through the forms and under the whole of 
the cover, and yet without extending beyond its limits. 
There are these advantages attending this plan : the forms 
being next to the glass cover, no considerable thickness of 
balsam has to be looked through when they are seen under 
the microscope, and by the use of the pin's head the 
quantity of balsam used may be so gauged as to necessitate 
no after- cleaning of the slide from superfluous balsam. The 
slide is then placed on its edge half an hour or an hour, 
when any air-bubbles which may have been entangled by the 
forms will have found their way out of the fluid balsam by 
the edges of the cover, after which the slide may be put aside 
to harden the balsam gradually, or it may be exposed to 
heat not greater than the finger can pleasantly bear, when 
the balsam will harden more rapidly. 
The preservation of diatoms in a dry state is performed 
in the usual manner. 
A ring of gold size is made on a slide by means of the 
whirling table, and over this a ring of asphalt when the 
former is dry. When the asphalt is dry, or nearly so, the 
slide is heated until the asphalt becomes soft, when the cover 
with the forms on it, as above described, is quickly placed 
upon it, and its edges pressed with a needle-point, so that 
they adhere to the asphalt at every part. The mounting 
may then be finished by placing another ring of asphalt 
round the edge of the cover. By this plan the asphalt will 
not run under the cover and spoil the preparation. 
