PROCEEDINGS OF SOCIETIES. 235 
Also 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. 
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, apparently with effervescence. 
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 avery 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 magnesia. 
The form of the crystals also supports this view, though their 
minuteness renders the examination difficult. By far the greater 
Sketches of the crystals. 
number of the crystals presented a rhombic outline, the largest 
measuring in their longer diagonal 5755th of an inch. Some 
approximation to the measure of the angles was obtained by 
means of a doubly refracting prism fitting on to the eye-piece of the 
microscope ; the mean of several measures gave 106° nearly as the 
value of the obtuse angle (that of cale-spar being 105°5’). With 
regard to the prismatic-looking crystals occasionally seen, several, 
examined by favorable light, presented the figure a, 0. 
This form of rhomboid resembles that which was called by 
Haiiy the “inverse,” a peculiarity of which is, that its plane 
angles measure the same as the dihedral angles of the primary 
rhomboid. - 
The crystals of the so-called crystallized sandstone of Fontaine- 
bleau (which are carbonate of lime containing sand) are instances 
of this form. 
