16 
acetate of lead by sulphuretted hydrogen, and boiled 
with the precipitate for a time to decolorise it, was ex¬ 
posed to a cold of a few degrees below 0°C., when 
long prism shaped crystals were formed. 
Any foreign substance, or a crystal of this resin 
thrown into the alcoholic solution, assists the first form¬ 
ing of crystals very materially. 
Before cutting up the wood it is best to scrape off 
as much resin as possible, for this portion dissolved 
in alcohol and ether, crystalises quite easily. 
The precipitate occasioned by the acetate of lead, 
which is not soluble in ether, was mixed with alcohol 
and decomposed by a current of sulphuretted hydrogen. 
In the filtrate of this new precipitate crystals were 
formed when exposed to a temperature below 0°C. 
These we have not yet examined. 
CRYST ALINE FORM. 
We now come to the crystaline form of this fossil 
resin. 
The crystals are oblique rhombic prisms with ortho¬ 
diagonal faces. Sometimes an oblique end face is pre¬ 
sent behind. In the prevailing form the angles of the 
side faces m : m = 97 0 and 83 0 : the end face p to the 
orthodiagonal face o = 127 0 : the second oblique end 
face behind i\o — 128°; and p : i — 105°. 
The ortho diagonal face cuts off the acute side angle 
of the prism m. 
The crystals are lengthened in the direction of the 
orthodiagonal: m in mostly very short. 
