DIATOMS: HOW TO FIND AND HOW TO PREPARE THEM. 57 
In recent gatherings, when the diatoms are clean, put them into 
a bottle containing equal parts of alcohol and water, where they 
may be kept as long as desired. When ready to transfer them to 
slides, all that is required with most varieties is to dip a few from 
the bottle with a pipette and put them on the thin cover glass, and 
after placing the glass on a strip of mica or of tintype, keep the 
whole at a red heat until the organic matter is destroyed and only 
the shells remain in white powder. ‘The favourite method of Dr. 
Lionel Beale, is to place all diatoms, whether recent or fossil, in a 
platinum cup, and then keep them at a red heat for several hours, 
or until the carbonaceous matter disappears, leaving a pure white 
ash. Dilute nitric acid is then used to dispose of the carbonates, 
and the remainder is washed. 
The following simple method of cleaning diatoms I learned of 
Prof. H. L. Smith, of Hobart College. Boil for 30 to 60 minutes 
in strong soap suds, wash thoroughly in soft water to get rid of 
foreign material, such as sand, flocculent matter, etc. How to accom- 
plish this will soon be explained. On examination of the material, 
if organic matter be still present, put the mass into a test tube or 
other suitable vessel, and, after settling, completely turn off all 
supernatant water and add four or five times its bulk of nitric acid, 
and while boiling throw in small fragments of bichromate of potash 
to bleach. Some prefer chlorate, but the bichromate is sufficient, 
and danger of explosion is avoided. When the organic matter has 
been destroyed, a higher temperature will be required to boil the 
acid, indicating that no more is needed. Probably five or ten 
minutes will be sufficient. Wash in rain water or that from melted 
ice until a drop evaporated on a slide shows no residue around the 
edge, leaving a clean slide of diatoms. Never use hard water, for 
the lime in it will cause all flocculent matter to cohere in masses. 
The methods given are all that is required for a large proportion 
of diatomacezeous material so far as disposing of organic matter is 
concerned. The sand and other indestructible matter must be 
eliminated by gravity. 
Guano, Monterey stone, material containing lime, &c., requires 
harsher treatment and much more time. 
Guano should be boiled at least two hours in soft water, or as 
long as any colouring matter can be turned off; then proceed as in 
fossil earths, 
Stonelike masses must be broken down by boiling in a strong 
solution of soda crystals. After disintegration wash and boil for 
20 to 30 minutes in strong nitric acid, and while yet boiling add 
about an equal quantity of muriatic acid, and continue the boiling 
from 20 to 30 minutes longer. After washing out the acids boil in 
pure sulphuric acid until the mass becomes inky black, then throw 
in fragments of bichromate of potash, and continue the boiling until 
