OF MICROSCOPIC OBJECTS. 65 
sifting through coarse muslin, which will retain the Algw, 
&e. The process of cleaning will vary according to circum- 
stances. Some gatherings require to be boiled only a few 
minutes in nitric acid; but the more general plan, where 
they are mixed with organic or other foreign matter, is to 
boil them in pure sulphuric acid until they cease to grow 
darker in’colour (usually from a half to one minute), and then 
to add, drop by drop to avoid explosions, a cold saturated 
solution of chlorate of potash until the colour is discharged, 
or, in case the colour does not disappear, the quantity of 
the solution used is at least equal to that of the acid. 
‘This operation is best performed in a wide-mouthed ordinary 
beaker glass,* a test-tube being too narrow. The mixture 
whilst boiling should be poured into thirty times its bulk of 
cold water, and the whole allowed to subside. The fluid 
must then be carefully decanted and the vessel re-supplied 
once or twice with pure water, so as to get rid of all the 
acid. The gathering may then be transferred to a small 
boiling-glass or test-tube, and—the water being carefully 
decanted—boiled in the smallest available quantity of 
nitric acid, and washed as before. This last process has 
been found necessary from the frequent appearance of 
minute crystals, which cannot otherwise be readily dis- 
posed of without the loss of a considerable proportion of 
diatoms. 
I may here mention that the washing-glasses used by 
Mr. Rylands are stoppered conical bottles varying in 
eapacity from two ounces to one quart; the conical form 
being employed to prevent the adherence of anything to the 
side: they are stoppered, to render them available in the 
shaking process about to be described. 
The gathering, freed from acid, is now put into two inches 
depth of water, shaken vigorously for a minute or two, and 
allowed to subside for half an hour, after which the turbid 
* These glasses are round, about six inches high, and usually contain 
about eight ounces. They are rather wider at the bottom, tapering 
gradually to the top, and may be generally procured at the chemists, &c. 
F 
