652 
THE TROPICAL 
AGRICULTURIST. 1 April 1, 1904. 
obtaiuable. The Straits planters are a go-a-head lot, 
and will be keen rivals to Ceylon. We must see to it 
that Ceylon robber keeps ahead of our more eastern 
rivals, and that our rubber, like our tea, shall be 
second to none. 
In the interests of Ceylon rubber we give the results 
of Dr. Weber's investigations mentioned above, and 
commend them to the notice of all planters. 
STATE OF EUBBEK IN THE LATEX. 
On investigating Castilloa latex with a view to deter" 
mine the nature of the process of coagulation, it very 
soon became perfectly clear that the coagulation of the 
latex is not due to any specific property of the india- 
rubber in the latex, but is simply a matter of the 
coagulation of the albuminous matter contained in the 
latex. The India-rubber substance is not dissolved in 
the latex, but is emulsified or suspended in it. Now, if 
in a suspension of this kind we have at the same time 
albumen in a state of solution, anything which will 
coagulate — i.e., render insoluble or precipitate — the 
albumen will at the same time result iu the suspended 
matter being carried down by the precipitating or 
coagulating albumen. The capability of coagulation 
exhibited by all kinds of rubber lat^x with which 1 am 
acquainted depends, therefore, entirely upon the pre- 
sence in it of coagulable albuminous substances, and 
the so-called coagulation of india-rubber is therefore a 
process exactly on a par, in both its chemical and 
physical aspects, with the clarification of wine or beer 
by means of such albuminoids as isiuglass or gelatine. 
There is only this difference — that in the case of rubber 
latex to carry down the rubber suspension we need not 
add any albuminous matter, as it is already a regular 
constituent of the latex. 
In the above-mentioned facts lies the explanation o^ 
the further fact that the coagulation of rubber latex 
can be accomplished by any one of the numerous re- 
agents capable of coagulating albumen. The process of 
coagulation is neither assisted nor retarded by the pre- 
sence of the suspended (emulsified) india-rubber. On 
th eother hand, the readiness with which coagulation 
does take place depends very considerably upon the 
exact nature of the albuminous matter present in the 
latex, as well as npon the presence of certain inorganic 
salts. It is for this reason that two different kinds of 
latex, of difierent botanical origin, although both may 
contain the same amount of albuminous matter, cannot 
be coagulated neither equally easily nor even, per- 
haps, by the same means. 
COAGULATION BY HEATING. 
This latter point is particularly strongly marked in 
the case of the simplest process of coagulation — namely, 
coagulation by heating. Some kinds of latex can be 
boiled for a practically indefinite time without any 
coagulation taking place ; others will coagulate long 
before they reach boiling point. But this difference 
disappears the more energetic the coagulating agent 
we employ. Thus it will be found that most kinds of 
latex are coagulated by the addition of small quantities 
of either acetic or dilute mineral acids, but the time 
required for the complete coagulation of different 
kinds of latex by any of these acids varies rather 
considerably. On the other hand, all kinds of latex 
undergo immediate coagulation on the addition to them 
of a solution of tannic acid, hydrofecrocyanic acid, or 
mercuric chloride, or nitrate. 
Of course, rubber prepared by any such process of 
coagulation always necessarily contains also all the 
albumen present in the rubber milk. This amount 
varies not inconsiderably in different kinds of 
latex, and we therefore find that some brands of rubber 
contain very varying amounts of coagulated albumin- 
ous matter. There is not more than from 2 to 3 per 
cent, of it in Para rubber, whereas coagulated Castilloa 
rubber contains often as much as 11 per cent. 
PUTKESCENCE IN " HEATED " RUBBER, 
Now it is just this albuminous matter in the rubber 
which ia always at the bottom of the trouble of the 
fatal appearance of " heating " in the rubber. Albumen 
coagulated or otherwise, as everybody knows, becomes 
very early putresoid, and this putrescence is a process 
due to the action of certain specific micro-organisms 
upon the albumen. These micro-organisms it is im- 
possible to keep out of the rubber latex, and thus out of 
the coagulated rubber, and if the rubber be shipped wet 
inside we obte,in all the conditions favouring the rapid 
spread of putrescent fermentation throughout the 
rubber. This process sooner or later also effects the 
rubber, which then exhibits an appearance much as it 
it had been heated to its melting temperature ; hence 
the popular description of it as " heated." As a m itter 
of fact, if the rubber is free from albumen, it will 
never undergo thi.9 change. Tlie highest temperature 
possible in a ship's hold in tropical latitudes is entirely 
iuaufifieient to affect the rubber. 
CO-.GULATION BY THE SMOKING PEOCESS. 
I have above pointed out that this invidious action 
of albumen in the india-rubber is contingent upun the 
presence at the same time of water. Accordingly, 
we fiad that if rubber containing albuminous matter 
be shipped in a perfectly dry condition, any detri- 
mental action of the former is prevented. Of course, 
the same result may be obtained, irrespective of the 
presence of moisture and albuminous matter in the 
rubber, by incorporating it, preferably in tbe process 
of coagulation, with some antiseptic material. This 
is what is done by the smoking process in the case 
of Para rubber. It is well known that the smoking 
process can only be carried out by means of a low 
fire, smouldering rather than burning. The sm eke of 
such fires is characterised by the presence in it o,f 
acetic acid, methyl alcohol, acetone, creosot, and a 
number of empyreumatio substances. The smoking 
process'consists simply in a fractional coagulation — as 
Opposed to the usual coagulation in bulk — each of the 
skins or layers which is added to the previous ones at 
each dipping of the paddle in the rubber milk being 
coagulated by exposure to the above described 
smoke, 
ACETIC ACID, THE AGENT IN SMOKE, 
The coagulating agent in this smoke is, no doub t 
the acetic acid, but it is not improbable that mIso some 
of the other constituents of the smoke play some part 
in it, and it is quite certain that the creosot and similar 
phenolic bodies of the smoke act as powerful antisep- 
tics, and thus prevent the albuminous matter of Para 
rubber, although the latter always contains a consider- 
able percentage of moisture, causing tbe " beating " of 
the rubber during tiansit. 1 have, indeed, never heard 
o£ "heated " Para; not even as a very rare occurrence. 
On the other hand, Negrohead, although it contains 
the same intrinsic rubber substances as Para, is very 
liable to heating. 
All the above considerations are of the utmost im- 
portance in regard to the question of procedure in the 
preparation of rubber from all kinds of rubber latex ; 
they form, in fact, the basis of the whole question 
coagulation. 
SHRINKAGE IN CRUDE BUBBEE, 
One of the greatest troubles in connection with 
crude rubber has alw-i.ys been its comparative im- 
purity, stated as " loss on washing " (shrinkage) by 
the manufacturer. Considerable improvements in 
this respect have been effected in the African grades 
of rubber, whereas the American, and also the Eastern, 
brands have been going worse and wrfrae in recent 
years. Of course, the " loss on washing " entirely con- 
sists of the moisture and the mechanical impurities 
contained in the crude rubber, and until quiet recent 
years manufacturers looked upon a washed rubber 
as an essentially pure article of its kind. But, as a 
matter of fact, many grades of rubber, even after 
washing and drying, are a long way from a real state 
