On March 12, 1998 I asked the expert Conch-L readership the question as to
the best desiccation technique for preserving microshells (up to 10 mm).  I
received many answers that addressed desiccation and preservation for
dissection or DNA analysis.  I then integrated the responses and issued the
following summary.  Here it is again to serve as a refresher or generate new
insights:

A. Definitions
1. Desiccation - to dry up; dehydrate.
2. Isopropyl alcohol (isopropanol) - C3H8O, usually used as rubbing alcohol.
3. Ethyl alcohol (ethanol) (alcohol) - C2H6O.
4. Hydrogen peroxide - H2O2, an oxidizing and bleaching agent.
5. Oxidize - to dehydrogenate; to remove hydrogen from. Good at deodorizing,
but does not desiccate.
6. Denature - to modify the molecular structure of (as in proteins or DNA)
or diminish some of the original properties.
7. Methanol - CH3OH
B. Desiccation
Isopropanol or ethanol can be used with equal success. Ethanol is most
commonly used in labs. Ethanol has a greater affinity for water, and because
of its smaller molecular size, theoretically it may penetrate and dehydrate
tissues somewhat faster. Whichever is used, the concentration of alcohol is
most important. 75% concentration will do the job, but the higher the
better. The higher the alcohol concentration the more water dehydrated from
the animal, desiccation is more thorough, and the faster the final drying
process.
Alcoholic beverages can be used. However, note that the "Proof" of the
beverage is twice the percentage of the alcohol content. Therefore, 140
proof rum has an alcohol concentration of 70% and would work the same as 70%
rubbing alcohol.
The ideal method is to use 10 times the volume of 100% alcohol as the volume
of the animal. This approach compensates for the dilution that occurs as
water is drawn out of the animal. Therefore, if you use a 75% concentration
rubbing alcohol the quantity should be increased by approximately 1/3. A
good approach to assuring as thorough dessication as possible would be to
replace the alcohol after a day or two; especially if the alcohol becomes
discolored. Because, remember that as water is drawn out of the animal the
concentration of alcohol is being diluted. Since the percentage desiccation
cannot exceed the percentage concentration of the alcohol, in order to
achieve 70% desiccation with a 70% alcohol you will have to replace the
alcohol several times until the dilution effect is eliminated (until the
alcohol no longer becomes discolored - yellowish). The remaining 30% of
water is eliminated via drying.
Denatured alcohols have denaturants added that will damage the animal and
which can also eat up the calcium carbonate in the shell. Do not use
denatured alcohol. Potable alcohols do not have denaturants added.
C. Preservation for Dissection
Preservation for dissection is best accomplished by storing in 70% ethanol.
Isopropanol will harden the animal to the point that it can't be dissected.
Ethanol in concentrations over 80% will also harden the animal.  (Note: I've
gotten differing opinions on this from different researchers doing
dissection work.  Personal preference appears to be involved.  Would like to
see more discussion about this from those actually doing dissection work.)
D. Preservation for DNA Study
Preservation for DNA study is aimed at stopping enzymes that destroy DNA.
Alcohol denatures enzymes that destroy DNA, but does not similarly denature
the DNA. The faster and better the alcohol does its job the less harm to the
DNA. Therefore, the optimal fluid to use is 90-100% ethanol (and it wouldn't
hurt to change the fluid once). However, in a pinch use the best you can get
and change the fluid a few times. Dr. Rosenberg indicates that methanol can
also be used to preserve for DNA studies.
Note: Be careful. Ethanol sold in drug stores is often denatured. Do not use
denatured alcohols.
E. Some Comments On Use of Hydrogen Peroxide
Hydrogen peroxide does have useful applications. However, it is not a
desiccant and should not be used for this purpose. It is an oxidant and can
do a good job of deodorizing by destroying odoriferous compounds. Since it
can also dissolve some of the soft tissues of mollusks, it may make it
easier to flush out microshells. Hydrogen peroxide is a bleaching agent, and
like bleach it can harm the pigments in shells. If it is used, soaking
should be restricted to no more than a few hours and the shell should be
thoroughly rinsed afterwards.
I hope this summary will be useful. Additional comments are welcome. Look
for an update of this summary in the event I receive technical corrections
and other useful information.

Marlo
Merritt Island, Florida