April 1, 1904.] THE TROPICAL 
AGRICULTURIST. 
653 
of pnrity. Thus, taking washed and dried fine Para 
we find that it contains on an average — 
Rubber ... ... 910 per cent, 
Resiuous matter .. 2'5 ,, 
Albaminona matter ... 3 ,, 
Mineral matter ... 05 ,, 
A considerable number of grades of washed rubber 
will be found to contain still up to 18 par cent, of im- 
parities of this kind. 
IMPOnXANT TO THE RUBER PLANTER. 
Now it is evident that the rubber planter, in approach- 
iun the question of the preparation of his rubber, 
should make the utmost of the opportunities he 
possesses of bringing upon the market only products 
of exceptional qunlity ; in fact, he should sell rubber 
only in a condition approaching chemical purity, and 
the question therefore is how to produce such rubber. 
CHIEF IMP0BITIE9 OF KUBBEB. 
I have already stated that the chief impurities of 
rubber are, besides water, the mechanical impurities, 
such as saud, earth, and vegetable fragments of every 
description ; furthermore, resiuous and albuminous 
matter. Of these impurities all, with exception of 
the last two, are easily avoided— at least, in all those 
kinds of latex which do not coagulate spontaneously 
the moment they issue from the trees. Ihis is 
certainly not the case with the latex produced by 
either Hevea or Castilloa — the only rubber trees cul- 
tivated on a large scale at the present time. 
STRAINING THE LATEX. 
To free the rubber from mechanical impurities 
amounts, of course, simply to removing these im- 
purities from the latex. This is best done by strain- 
ing the latex through some suitable fabric. The one 
known as "butter cloth," or "cheese cloth," answers 
this purpose very well, and it is moreover very 
eheap. In the case of Uastilloa milk, it is absolutely 
essential to dilute the milk with at least four volumes 
of water before straining. In the case of Hevea milk 
there is not quite the same necessity to dilute it 
before straining, but the operation will prove much 
more expeditious after addition of about two volumes 
of water. Very important is it not to touch the 
straining surface with the hand, or to rub it with 
a brush or some other implement, in order to hasten 
the passage of the milk through the cloth, as doing 
this invariably results in the cloth becoming clogged 
with coagulating rubber. Should the diluted latex run 
too slowly through the strniner, the latter should be 
shaken by causing it to oscillate rapidly in a horizontal 
direction. If this is done right from the start the 
latex will pass through very freely. It is also per- 
haps scarcely necessary to point out that the strainer, 
when not in use, should be kept in water. A strainer 
which has been used and is then allowed to get dry 
will be found useless for further work, as it is com- 
pletely covered by a fine coating of coagulated rubber. 
TO GET KID OF THE ALBUMEN. 
In preparing the rubber from this latex freed from 
its unavoidable mechanical imparities, we shall now 
have to make up our mind whether we desire to 
produce the rubber free from albuminous matter. 
This is the course I most strongly recommend. 
India-rubber freed from this substance may not im- 
mediately commend itself in its true merit to rubber 
manufacturers, but its superiority will soon become 
manifest and be recognised by a higher price. To 
E reduce such rubber the following procedure would 
ave to be adopted : — 
To every gallon of the rubber latex from j oz. to 1 
02. of formaldehyde (formaline, •lO per cent, solution) 
is added, the latex well stirred, and allowed to stand 
for one hour. Then to each gallon of latex a solution 
of I lb. of sodium sulphate (commercial) in one pint 
of boiling water is added, while still hot, and the 
mixture stirred for some time, Coagulation may take 
place immediately, or after several hours' standing, 
(iicoording to the ocmditiou (age) of the lates. Great 
care must be taken to use a sodium Bnlphate of entirely 
neutral (not acid) reaction: 
The cake of rubber thus formed is liable to contain 
numerous cavities, including some of the mother liquor. 
It shonld therefore be washed upon a corrugated 
rubber washing machine until the sheets of rubber 
exhibit their full strength. They should then be 
thoroughly dried in a dark but well-ventilated shed 
until absolutely dry. 
Rubber prepared in this manner will be found free 
from every trace of albuminous matter. It is of a 
degree of purity greatly surpassing the finest Para 
rubber ever produced, and therefore contains a percen- 
tage of pure rubber exceeding that of every known 
rubber quality. Its only impurity consists of about 2 
per cent, of a viscous resinous matter, the removal of 
which is scarcely worth while. 
COLOURLESS RUBBER. 
This same treatment, in like manner, ia also appli- 
cable to Castilloa latex. In both cases the rubber 
obtained forms an almost colourless substancoi which 
to anyone associating with rubber a Colour ranging 
from a medium brown to black must appear startlingly 
unlike rubber. 
THE PROCESS FOB NON-COAGULATED BtJBBER. 
Strictly speaking, this method of preparing the 
rubber is not coagulation at all. If it were, it is ob- 
vious that in accordance with what I said above about 
the nature of the coagulation process, the coagulated 
albumen would be contained in the rubber, whereas 
rubber prepared in the above-described manner ia 
entirely free from albumen. 
What actually happens in this method ia this: 
The diluted rubber milk, freed from all its mechanical 
impurities by straining, is to begin with rendered non- 
coagulable by the addition of the formaldehyde, which 
combines to a readily soluble compound with the albu- 
minous matter present. On now adding to the rubber 
milk the solution of sodium sulphate the rubber 
substance rapidly rises to the top, where at first it 
forms a very thick, creamy mass, the individual 
globules of which rapidly coalesce. The coalesced (and 
as a matter of fact, not coagulated) mass, on being 
worked upon the washing rollers, undergoes a very 
curious polymerisation process, and thereby rapidly 
acquires the great strength and toughness so charac 
teristic of high-class india-rubber. 
COAGULATING AGENTS. 
Considering now the process of coagulation proper 
of the india-rubber latex, the most important point 
is obviously the selection of the coagulating agent, 
and while one would naturally be inclined to use one 
possessing as energetic as possible a coagulating 
action, it is, on the other hand, imperative not to 
employ any material capable of subsequently detri. 
mentally affecting the india-rubber. The reagents 
capable of coagulating india-rubber, as I have above 
shown at some length, are exactly the reagents 
capable of coagulating albumen. These are formic 
acid, acetic acid, and a considerable number of 
organic acids, phosphor-tungstic acid, potassium- 
bismuth iodide, potassium-mercury iodide, hydrofer- 
rocyanio acid (yellow prussiate and acetic acid,) 
tannic acid, chloral hydrate, phenol, and picric acid- 
Quite a number of these reagents are of too ex- 
pensive a nature to be used otherwise than on a 
laboratory scale. Several of them, notably the in- 
organic of the above named compounds, as also 
hydroferrocyanio acid and picric acid, would be 
highly undesirable compounds in india-rubber. There 
remain, therefore, only to be considered for practical 
purposes formic acid, acetic acid, tannic acid, ancj 
pheool, 
TANNIC ACID — THE QUICKEST AGENT, 
Of these tannic acid will be found to have the 
quickest and most energetic action. I have not so far 
had an opportunity of experimenting with it on a 
large scale, On the laboratory scaje the resulta ob- 
