62 PREPARATION AND MOUNTING 
place), they may be placed in a small phial with a little 
distilled water. 
There are many cases in which the above method will not 
effect a perfect cleansing, as certain substances with which 
diatoms are frequently mixed are not soluble in nitric acid. 
For this reason the following method is resorted to :—Take 
a quantity of the matter containing the Diatomaceze and 
wash first with pure water, to get rid of all the impurities 
possible. Allow this to settle perfectly and decant the 
water. Add hydrochloric acid gradually, and when all 
effervescence has subsided, boil for some minutes by aid of 
the lamp. When cool and the particles have subsided, 
decant the hydrochloric and add nitric acid. The boiling 
must then be repeated until a drop of the liquid when 
placed under the microscope shows the valves or “ frustules ” 
clean. After allowing the diatoms to settle, the acid must 
be decanted, and pure water substituted. The washing 
must be repeated as in the former process until all the 
remains of crystals or acid are removed, when the specimens 
may be preserved in small phials. 
Such are the usual modes of treating the Diatomacee, 
but there are certain cases in which particular methods are 
required to give anything like perfect results. Persons of 
great experience combine a variety of treatments, and thus 
obtain better and more uniform specimens. Perhaps it will 
be advantageous to give the young student the process 
adopted by one of the most successful preparers of these 
objects; but I will first state the different methods of 
mounting the cleaned diatoms dry: how to employ Canada 
balsam and fluid in their preservation will be elsewhere 
described. 
It was before stated that diatoms when cleansed might 
be preserved in small phials of distilled water. When re- 
quired for mounting, shake the phial, and with a thin glass 
tube or rod take up a drop of the fluid and spread it upon 
the surface of the slide in the desired position. This must 
then be allowed to dry gradually, or by the aid of the lamp 
