CHLOROPHYCEAE 
181 
Material for mounts of frustules of living forms 
may be obtained by skimming off the brownish scum found on ponds, by 
squeezing out water weeds, by scraping sticks and stones which are covered 
at high water, or from the mud of filter beds and pumping-works, or in 
other places. The material is put in a dish of water, and after it has settled 
the water is decanted. This is repeated until the water will clear in about 
half an hour. The sediment is then treated with an equal bulk of sulphuric 
acid, after which bichromate of potash is added until all action ceases. 
After a couple of hours the acid is washed out. To separate the diatoms, 
place the sediment in a glass dish with water, and when the water becomes 
clear give the dish a slight rotary motion. This will bring the diatoms to the 
top, when they may be removed with a pipette and placed in alcohol. To 
mount, place a number in distilled water, evaporate a few drops of the 
mixture on a cover-glass, which is then mounted on a slide in balsam. 1 
It is better to use a very slight smear of Mayer’s albumen fixative 
to prevent the diatoms from floating to the edge of the cover. 
Many scouring soaps and silver polishes contain large quantities 
of fossil diatoms, and the diatomaceous earths are particularly rich. 
Diatomaceous earths from Cherryfield, Maine, and from Beddington, 
in the same region, are the richest we have seen. The deposits at 
Richmond, Virginia, have long been famous. In some of our western 
states there are deposits 300 feet thick, with 80 per cent of silica, 
the silica being the valves of diatoms. 
Break up a small lump of such material and boil it in hydrochloric 
acid. An evaporating dish or a test-tube is convenient for this 
purpose. Let the diatoms settle, pour off the acid, and then wash 
in water. As soon as the diatoms settle, the water should be poured 
off. The washing should be continued until the hydrochloric acid 
has been removed. When the washing is complete, pour on a little 
absolute alcohol, and after a few minutes pour off the alcohol and 
add equal parts of turpentine and carbolic acid. The material will 
keep indefinitely in this condition, and may be mounted in balsam 
at any time. In making a mount, put a little of the material on a 
slide and allow it to become dry, or nearly dry, and then add the 
balsam and cover. If the balsam should be added too soon, the 
diatoms are likely to move to the edge of the cover. 
We have had excellent results with the following method: After 
washing in water, keep the diatoms in 5 per cent formalin. To 
1 From a review of Dr. Wood’s paper on “Diatoms,” Journal of Applied Microscopy, 
March, 1899. 
