IN THE WOOD OF THE WELWITSCHIA. 107 
I found, as I believe you had already, that when the spicula 
were immersed in dilute hydrochloric acid, even though they re- 
mained in the liquid several hours, there was no action on the 
crystals. 
Also that when the spicula were placed in a platinum spoon 
with hydrofluoric acid and heated, and when the same was done 
with a solution of caustic soda, there was no apparent action on 
the crystals. 
On the other hand, when the spicula were boiled in nitric acid, 
the crystals disappeared. 
I then found that when a few spicula were carefully burned by 
heating them on platinum foil over a small spirit-flame, a white 
ash remained of the form of the spicula; and when this ash, 
moistened with water, was examined by the microscope, it was 
found to be made up of a congeries of the crystals unaltered in 
form, and acting on polarized light. 
When a drop of dilute hydrochloric acid was added, the crystals 
disappeared, and, I thought, with effervescence. I then made the 
following experiment. 
A quantity of the spicula was collected which weighed 0'105 
gr.; this was carefully burned as before; the ash weighed 0:010 
gr., or just 10 per cent. : water added to the ash, the liquid slightly 
restored the blue of reddened litmus; a drop of hydrochloric acid 
added, the ash dissolved with brisk effervescence ; and when this, 
neutralized by ammonia, was tested by oxalate of ammonia, a con- 
siderable precipitate formed. 
The supernatant liquid was removed, and tested by phosphate of 
soda; but a very minute, if any, precipitate was thus formed. 
This experiment shows that the substance examined is essen- 
tially carbonate of lime, possibly with a little carbonate of mag- 
nesia, 
The form of the crystals also supports this view, though their 
minuteness renders the examination difficult. By far the greater 
Sketches of the crystals. 
b 
number of the crystals presented a rhombic outline, the largest 
measuring in their longer diagonal ygyoth of an inch. h obtained 
1 
