40 
REPORT ON THE CAOUTCHOUC OF COMMERCE. 
Of these various methods that by the cautious application of dry 
heat is generally accounted the best, and the Para Caoutchouc of 
the best description is prepared in this manner. The action of the 
Urucuri and other nuts {Attalea excels a, Mart. &c.) I cannot 
altogether understand • I am inclined to look upon it as only a ready 
means which has suggested itself of drying the Caoutchouc without 
injuring or affecting its quality. The heat of a naked fire would if 
great care were not taken burn the Caoutchouc ; and because it is a 
convenieift and safe method, and fulfils the desired conditions, it may 
have at last come to be looked upon as essential. Certain I am that 
it has no blackening action as is so frequently stated. That this 
blackening is due to atmospheric influences can be easily verified by 
any one taking a piece of thick Para Caoutchouc, cutting it through 
so as to expose the white or yellowish white centre, and notice how 
soon the white will be changed to black by the influence of light 
and air.* The cautious application of heat especially if supplemented 
by the fumes of melted sulphur, which I believe is used in Para, 
would and does furnish the best 'prepared Caoutchouc. Of natural 
heat, or allowing the Caoutchouc to coalesce and the water to 
evaporate spontaneously, though the Caoutchouc is in as good a 
condition as the tree can yield it, yet it always lias masses of bark 
adhering to it, and necessitates a second visit being paid to the tree, 
and this alone is objectionable as the scene of operation has constantly 
to be shifted. 
Of the addition of various substances such as alum and certain 
plants the action seems to be similar to that of rennet on casein, 
but I have had no opportunity afforded me of testing the precise 
action of these substances. The chief plant used in Nicaragua 
is the common Ipomcea bona-nox , L. = Calonyction speciosum , 
Choisy. a convolvulaceous plant. This was identified with the 
“ achete ” by Dr. Seemann at my instigation. The use of alum as 
before stated is very much used in Para. The treatment with an 
acid (Acetic ?) can only be put down as a conjecture at present. 
The action too of Liquor Ammonia is generally said to retard coa- 
lescence ; whether its action be to stay this coalescence in order first 
to get rid of as much aqueous liquid by the difference of density I 
do not know. In the wet processes as distinguished from the dry 
methods of preparation, viz., by the addition of hot, cold, or salt 
water, &c., they are open to the objection of retaining moisture in 
* Caoutchouc, like other hydrocarbons, absorbs oxygen readily, and thus undergoes 
the change indicated. The resins ( albine and fhictvile) found in gutta percha appear 
but to b$ gutta percha plus oxygen. 
