654 
ON THE COPAL OF ZANZIBAR. 
and nitrate of potash; the musket and gun powders contain carbon in addition to the 
above-named ingredients. To prepare these powders, the ingredients are beaten from 
three to six hours with a proportion of water varying from 6 to 14 per cent,, according 
to the nature of the mixture ; the powder is condensed by means of the hydraulic press, 
with a pressure of from 30,000 to 100,000 kilos., graining of the powder, and pressing 
and drying it according to the methods employed for the black powder. In order to in¬ 
crease the balistic power, the relative proportion of picrate of potash in the mixture must 
be increased. For musket powder it has been proved that not more than 20 per cent, of 
picrate of potash is required, while for gunpowders its proportion varies from 8 to 15 per 
cent. This component (picrate of potash) is of a beautiful golden-yellow colour, and 
crystallizes into prismatic needles possessing a brilliant reflection ; it is insoluble in 
alcohol, but soluble in about 260 parts of water at 15° or 14 parts of boiling water. 
Heated with care, it becomes orange-red at a temperature of 300°, but, on cooling, it 
assumes its original colour. Heated to 310°, it detonates with violence. The researches 
of M. John Casthellaz on the action of nitric acid on phenic acid improved the method 
of manufacturing picric acid, and produced chemically pure picrate of potash at such a 
reasonable price that the new powders are not more expensive than ordinary black 
powder. 
MM. Desiguolle and Casthellaz give the following proportions for preparing defla¬ 
grating mixtures with coloured flames •— 
Picrate of ammonia . 50 
Picrate of iron k . 50 
Picrate of ammonia . 48 
Nitrate of barytes . 52 
Picrate of ammonia . 54 
Nitrate of strontian . 46 
— Chemical News ; abstracted from the Bulletin de la Socie'te d’Encouragement. 
Golden fire 
Green fire 
Red fire . 
ON THE COPAL OF ZANZIBAR. 
Extract from a Letter from John Kirk, M.D., F.L.S., dated Zanzibar , March 20, 1868. 
The vegetation along the creek of Dan Salam * consists of many curious, and, to me, 
unknown bushes, with heavy timber scattered here and there; among them was the 
Trachylobium M ossambicense, Kl., distinguished by its rounded head of glossy leaves, 
w ith white groups of flowers projecting from the points of the branches. This is the 
“ M’ti Sandarusi ” (Tree of Copal) of the natives; and from it one variety of Copal is 
obtained. On examining the tree more closely, the trunk and main limbs were seen to 
be covered with the clear resinous exudation, now brittle and hard; from the upper 
branches it dropped down on the ground below, but not in a fluid state. To judge by 
the appearance it presented, I should say that the resin soon dries and hardens after 
being exuded, but must be easily broken off by violence; pieces of various tint and form 
were collected, some with insects imbedded; but all presented a smooth polished ex¬ 
terior, quite free from any pitting or “gooseskin” found on all kinds dug up from the 
ground. This sort is known in trade as “ Sandarusi ya m’ti,” or Copal from the tree; it is 
exported in considerable quantity to India, but not to Europe. Having thus established 
the source of one sort of Copal to be the Trachylobium, and transmitted the resin with 
full herbarium specimens of flower and fruit (which, if I mistake not, are to this day 
desiderata in all our collections), let me briefly state my reasons for thinking that in this 
tree we have the source of the older Zanzibar Copal, the semifossil or bituminized resin 
known in the English market as “ Aniine,” and which is the most valuable of all resins 
for the manufacture of varnish, exceeding anything produced on the west coast for 
hardness, elasticity, and polish. 
* [Dan Salam is stated in the letter to be a spacious creek opposite the southern end of 
Zanzibar Island.—E d.] 
