small amount of nitric acid is added (about | ml of acid per 250 
ml of water) to hasten hydrolysis of the organic silicate within 
the wood. Since prolonged or repeated breathing of ethyl sili- 
cate vapor can be harmful, contact with this reagent should be 
minimized as much as possible. 
Removal of all organic matter from the silica-impregnated 
specimen of plant material to form a lithomorph, i.e., a pet- 
rifaction free of organic matter, is accomplished ina fume hood 
by oxidation with Schulze’s solution — a mixture of concen- 
trated nitric acid and crystals of potassium chlorate (Jane, 
1970). The specimen is placed in the acid in a beaker and then 
the beaker is heated gently. While warm, crystals of potas- 
sium chlorate are carefully added. Oxidation is continued until 
all organic matter is removed. Time of treatment varies from 
only afew hours to several days or more, depending on the size 
and permeability of the specimen. Completeness of removal 
can be tested for by heating the specimen in concentrated 
sulfuric acid. Should a trace of organic material be present in 
the lithomorph, it will become discolored and develop a yellow 
tinge. Larger amounts of organic material will turn the synthe- 
tic petrifaction black. After oxidation, the lithomorph is care- 
fully washed and then stored in water. Upon drying out, there 
is a tendency for silica to develop minute fractures and to 
partially granulate. Slides for microscopic study in white light 
are prepared by gently macerating the lithomorph and mount- 
ing the macerate upon the slide with glycerine jelly. 
Discussion of the Technique 
This technique differs from that of Drum (1968a, 1968b) in 
that the silicification is accomplished in molecular silicic acid in 
solution at pH conditions near neutral and the degree of impre- 
gnation is greater to the extent that the siliceous replica does 
not readily disaggregate upon loss of its organic template. 
Further improvement of the laboratory technique will prob- 
ably depend largely upon the successful modification of two 
factors. First, it will be necessary to achieve a more thorough 
penetration of mineral matter into the specimen, particularly 
within and across cell walls. This may require some chemical 
alteration or modification of the wood constituents to make the 
wood more permeable to fluid infiltration and more susceptible 
to silica uptake. Second, it would be desirable to render more 
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