April 1, 1903.] THE TROPICAL AGRICULTURIST. 65S 
a central ahed to be coagulated, cleaning oat the 
tins, etc., so that at the rate o£ 30 cents per day, the 
cost of collection can be pat down at 15 oenta per 
pound, a figure liable to modification if improved 
methods of extraction are forthcoming. The coat 
however, increases perceptibly when trees of a younger 
age are worked and in the ca^e of five to six year old 
trees, where the yield will probably not exceed one 
ounce of dry rubber per day the cost ia just doubled 
and it appears to me to be very doubtful, whether 
it is worth while tapping a tree unless an average 
of at least one ounce of dry rubber per day can be 
relied upon. With an improved tapping instrument, 
many more trees could be gone over, but 
even then the cost of extracting the rubber from 
younger trees will be considerable, to say nothing 
of the injury inflicted upon the tree, if the tapping be 
continued until an appreciable amount has been 
obtained. 
PEEPARATION OF MARKETABLE RUBBER. 
Coagulation of the latex should be effected im- 
mediately after it has been collected, for if allowed to 
stand even until the following morning, decomposition 
of the proteid matter will often set in, and the value 
of the rubber will be decreased. This is easily 
detected by the putrid smell which is given off by the 
latex, or in thd case of prepared rubber, by the dark 
coloured blotches, both of which can be entirely 
avoided by coagulating the latex immediately it is 
brought in from the trees. The rubber will then have 
only a slight, unobjectionable, characteristic odour, 
and will be of a light amber colour, deeping slightly 
with age. 
The composition of the latex of Heveai as given by 
Seeligmaun, * is as follows :— 
, Caoutchoao .. 32 per cent "J 
Nitrogenous matter (proteid) 2'3 V in solution. 
Salts .. .. 9-7 J 
Eeainoas matter . , traces. 
Water, slightly alkaline . . 65'6 per cent. 
The quality of " Para " rubber is due to some extent 
to the very small proportion of resinous matter con- 
tained in the latex. The latex, however, differs per- 
ceptibly in the per-oentage of caoutchouc it contains 
sometimes being of a creamy consistency with a 
yellowish tinge, while that from other trees has a 
more watery appearance and resembles skimmed milk; 
but as the latex from the various trees is not coagu- 
lated separately, this difference in the quality of the 
latex does not necessarily result in rubber of different 
grades. The Brazilian method of coagulating the latex 
by smoking it, has been described many times and 
need not be r epeated here. Rubber prepared by this 
method still commands the highest price of all 
native cured rubbers in the market, but whether 
the " Para " rubber so prepared will continue to 
occupy the premier position when pitted against rubber 
coagulated on more scientific principles is very doubt- 
ful. There will probably be a certain amount of con- 
servatism to break down, as is generally the ca^e 
when a new product makes its appearance on the 
market, but we may rest assured that so long as 
rubber continues to be used for the manifold pur- 
poses it is at present, that it will always command 
a remunerative figure ; and when prepared free from 
all foreign matter, and shipped in as dry a condition 
as possible, the probabilities are that it will eventually 
oust the " Para " rubber of to-day from its present 
position, for purity and freedom from moisture are 
what the manufacturer most desires. 
The preparation of the commercial article is quite a 
simple matter, and the cost but slight The method 
I have adopted is as follows ;— Before tapping, a 
little water, about sufficient to cover the bottom of 
the tin, was placed in each tin, in order to delay 
coagulation until the tins could be collected, which 
is generally about an hour after the incision has 
been made. As soon as the flow of latex has ceased 
* Seligmann, Le Oaoatchoc et la Gutta Peroha, 
the tins are collected, and their contents poured into 
a baain and an equal amount of water added. In 
this dilute state the latex was straiiipd through a 
fine muslin cloth and practic iHy all dirt, bits of 
bark, etc., were thereby reniovod : the latex is now 
ready to be treated with soma coagulating re-agent 
such as acetic, nitric or sulpliui ic acid, corrosive subli- 
mate, alum or other salt'i. All these substances and 
many others have the effect of collecting the rubber 
particles, which are suspended in a watery fluid, into 
a solid mass, which can then be pressed and dried. 
The coagulating power of the various acids differs 
considerably, but in all cases a very smiU amount is 
required. Parkins gives the following approximate 
figures, (loc.cit.) : — 
100 c. c. of pure latex are completed coagulated by 
0*1 gram Sulphuric Acid. 
100 c. c. „ ,, O'l „ Hydrochloric Acid. 
100 c. c. „ ,. 0-3 „ Nitric Acid. 
100 0. c. ,, ,, 0 95 ,, Acetic Acid. 
He also states that " if excess ha added then coiga- 
lation ceases to be complete." Tliis I have found to 
be the case with many of the acids I have employed 
though not so with acetic acid, even when ten times, 
the requisite amount has been adJel in which case 
coagulation took place instantly, so that it was im- 
possible to pour the latex out mto flit dishfs. The 
residue, however, was quite clear shewing that 
all rubber had been extracted. The great 
thing to remember is that tlia quantity of acid 
required depends upon the voluma of pwe latex, and 
no matter to what extent it is dihUed the amount of 
acid required to bring about complete coagulation 
remains the same. 
In actual practice I have found that acetic acid is 
by far the handiest to work with, as the range being 
so considerable, the quantity required to bring about 
complete coagulation is easily determined witliout 
going to the trouble of ascertaining the volume of 
pure latex to be coagulated. 
When the latex had been strained as described above 
a small quantity — roughly about a tea-spoonful to a 
pint of latex— of acid (acetic) wa- u Ided, and the whole 
stirred for a few seconds. If there were no signs of 
coagulation a few more drops of acid were added and 
stirred again, when usually it would gradually assume 
the consistency of thick cream, when it was im- 
mediately poured out into enamelled plates. The 
stirring and pouring out of the latex should be done 
as gently as possible, so as to avoid the creation of 
bubbles, which burst when the rubber is submitted to 
pressure, giving a roughened appearance to the 
surface. Enamelled plates are recommended in pre- 
ference to tins, as the latter are liable to become 
rusty, and are also acted upon by the various acids. 
After a lapse of t/iree or four hours coagulation 
should be sufficiently complete to allow of the rubber 
now in the form of a thiu solid cake and of a pure 
white colour, being taken out of the dishes and 
submitted to pressure, so as to express as much of 
the moisture as possible. Any kind of pressure may 
be employed, but something after the style of the 
old fashioned English wringing machine will probably 
be found as effective and inexpensive aa anything 
that can be devised. 
The advantage of adulterating the latex and then 
coagulating by some re-agent may not at first sight 
seem quite apparent, but unless some such principle 
be adopted, it will only be found possible to prepare 
a small per-centage in the form of thin sheets, by far 
the greater amount coagulating in the tins before 
they are removed from the trees. Such rubber will 
be in the form of irregular lumps will be difficult 
to dry, and will contain a certain amount of impurity 
no matter how carefully the tapping be conducted 
Moreover, unless some means of assisting coagulation 
be resorted to, difficulties are often esperienoed in 
wet or cloudy weather, decomposition setting in 
resulting in a discolouration of the rubber, an •vil 
odour, and coasenuently a depreciated value, 
