6 TuLK^ on Cleaning and Freparing Diatoms, 
to subside, and the discoloured water poured off. This wash- 
ing operation ought to be successively performed until the 
supernatant water remains colourless, for by this means a 
great deal of very minute matter is advantageously got rid of. 
If it is thought advisable, the washed mass may now be 
subjected to the action of boiling sulphuric acid and chlo- 
rate of potash, according to the method described by Mr. 
Arthur M. Edward, in ^ Jour. Mic. Soc.,^ vol. vii ; or if not, it 
may at once be transferred, if of considerable bulk, into a 
Florence flask ; but if of only small amount, into a test-tube 
six inches long and one inch diameter, allowed to settle — 
the supernatant water being poured off as close as possible — 
covered by a quantity of strong nitric acid, sp. gr. 1-5, equal 
to its own bulk, and boiled for five or ten minutes. It is 
then poured into the large six -inch bottle, which should^ be 
about one half filled with clean water, with which it is well 
shaken, allowed to settle for twelve hours, when the acid 
water is poured from off it, and a similar amount of clean 
water again added to it. Again the fluid is violently shaken 
for upwards of five minutes, for the purpose of breaking 
down and getting rid of the flocculent siliceous matter or 
mucus with which the diatomaceous frustules are generally 
connected, and from which they can be completely separated 
by no other means that I am acquainted with, and for the 
knowledge of which fact I am indebted to the kindness of 
Dr. Greville, who communicated it to me. 
The mass is again allowed to settle, until the superincum- 
bent water appears tinged only with a slight milkiness ; the 
water is then poured off. This operation of washing is suc- 
cessively repeated until the water, after standing for half an 
hour above the settlings and examined under a microscope, 
is seen to contain in suspension no very minute siliceous 
particles. Any larger particles which may be present will 
have subsided along with the forms, and will be got rid of in 
the next, the most important, operation. 
The mass is now placed in a small, thin, flat-bottomed, 
porcelain evaporating basin, say of two and three-quarter 
inches diameter and half an inch deep, with so much water as 
will half fill the basin ; the latter is put upon a table, and its 
contents allowed to subside, but not quietly, for during the 
subsidence a very gentle whirling or gyrating action is given to 
the water, similar to that by which the gold-washer separate 
the gold from the gravel in his round, iron washing-vessel. 
The diatomaceous frustules being comparatively light and of 
large superficial area, are more readily acted upon by the 
moving water than the solid, small masses of siliceous matter 
