688 
TtlE: TKOPICAti AGRICULTURIST. [April 1, l908. 
of perfection, anrl yet the limits of its furtlier ex- 
tension have probahly been readied by the insuper- 
nble barrifr of a climate so insabibrions that the 
Caucasian's life is one endless confiiefc with disease 
and when not engaged in active comViat with some 
form of malarial poisoning his energies are concen- 
trated npon battlowith the var'ous insect or animal 
pests that malre life a bnrden in such regions. 
Finally we have estiniafps given, which will he 
closely RCinitinised by Oevlnn planters, who 
can readily compare the fig'nres with their 
eTperiencp by reniemberine: that the American 
dollar is equal to abont three of orir rupees 
in value— the hectare heinsf 2i acres, the 
" cacao farm " estimated for, is one of 40 
acres. The ontlav. therefore, to the end of 
the 4th year is R262 per acre, but the cost 
of land is not counted and other expenses 
are expected to he defrayed by " catch 
crops." We make no further comments, 
save that so early as the fifth year, an 
" income," or rather gross return from the 
cacao crop of over E5,000 (or R125 per acre) 
is expected, which rises by the 9th year to 
R2l,000 or over R.500 per acre, resultine in 
a net profit of R3.37 per acre. Very rich 
must be the soil and flourishing the cacao 
trees that can give such results. 
4> 
INDIA-RUBBER. 
The Chemistry of India-Rubber.— By Carl 
Otto Weber, Ph.D. Pp. x + 314. (London : Ohas. 
Griffin and Co., Ltd.), Price 16s net. In the 
volume before us, the author has applied himself 
specifically to the chemistry of India-rubber, and 
incidentally to that of its various substitutes. It 
may be said at once that the result is an emi- 
nently useful contribution to the literature of 
India-rubber and its congeners. The book contains 
nine chapters ana an appendix. In the first chapter, 
which forms more than a third of the work and 
p;ives its title to the whole. Dr. Weber deals with 
the constituents of India-rubber, discusses their 
physical and chemical properties, and propounds 
in outline a theory of vulcanisation. The car- 
bohydrates present in crude " unwashed " rubber 
are first referred to, and then follows a useful 
little table showing the proportions of resinous 
extract obtained from the various commercial 
brands of technically- pure rubber by treatment 
with acetone. It may be explained that the im- 
portance of these "resins" lies in the fact that 
they allow the chemist to discriminate between 
a h'gh-quality rubber, such as Pard, and an 
inferior product like some of the African kinds. 
Passing on to indii-rubber proper, the author 
summarises the evidence which goes to prove that 
the pure rubber substance is a hydrocarbon of the 
terpene type. Oxygen, it is true, is alway.=! present 
in commercial specimens, but it is partly accounted 
for by atmo3i)heric oxidation and partly by the 
presence of an " insoluble " compound having the 
empirical formula of a hydrated terpene. This 
last, the author suggesits. may be an interme- 
diate product between india-rubber itself and the 
carbohydrates from which, perhaps, the various 
terpenes are manufactured in the cells of the rubber 
plant. Organic chemists have apparently found the 
chemistry of india-rubber somewhat unattractive. 
No doubt this is largely due to the -intractable 
nature of the compound ; for india-rubber, from 
this point of view, certainly possesses the 
defects of its qualities. It has few points of attack ; 
there are none of the carbonyl-, carboxyl-, aniido-, 
imido-, hydroxy- or methoxy-groups in which the 
organic manipulator delights ; it cannot be rpadily 
dissolved; and n fortiori, being a colloid, it 
cannot be crystallised. Nevertheless, it has one 
vulnerable spot, and t! e Achilles' heel in this 
case is found in the exi^itence of the ' ethvlene 
bonds ' pointed out by Gladstone and Hibbert. 
Much stress is laid upon the colloidal pro- 
perties of rubber as being the clue to" a proper 
understanding of its behaviour during manufacture 
—a disquisition on the colloidal state, lea.(ling up, 
however, to an interesting study of the'phenomena 
of vulcanisation. In the author's view the 
vulcanisation of india rubber by means of sulphur 
consists essentially in the direct addition of 
sulphur to the india-rubber hydrocarbon (poly- 
prene), with the formation of various polyprene 
sulphides. Combating the theory that the action 
of the sulphur is one of substitution instead of 
addition, the author rightly points out that if 
the former were the ease the vulcanisation of a 
ton of rubier would mean the production of about 
18,000 litres of hydrogen sulphide— a daily amount 
which would make the vulcanising rooms fairly 
reek with the gas. In reality, only insignificant 
traces are found there. The cold process of 
vulcanising by means of sulphur chloride is also 
discussed in detail. In the succeeding chapter 
the technical examination and valuation of india- 
rubber and gutta-percha are dealt with. But in 
this industry, as in so many others, our manu- 
facturers cling hard to rule-of-thumb methods ; 
stocks are bought on the strength of a cursory 
empirical examination ; and we read that, in 
consequence, different lots, supposed to be of 
identical quality, " often show the most absurd 
variations " when properly appraised by analysis. 
The following quotation speaks for itself : — 
" Pig iron, caustic soda, wood pulp, and scores of 
similar articles, costing comparatively speaking, a few 
shillings per ton, are bronght and sold on the basis of 
strict analytical standards ; but india-rubber, costing 
from £150 to £500 per ton, changes hands without 
either buyer or seller having more than a vague 
knowledge of its intrinsic value." 
A full description is given of the various india- 
rubber substitutes now so frequently used, and 
which consist either of recovered rubber from cast-ofF 
articles or of the products obtained by the action 
of oxygen, sulphur or sulphur chloride upon such 
substances as linseed or colza oils. Inorganic 
compounding materials, vulcanising agents, 
solvents, colouring matters and textile fabrics 
each claim a chanter. Analysts and technical 
chemists who are called upon to examine 
india-rubber will be grateful for the 
chanter on the analysis of rubber articles, 
with which the volume proper closes. 
Chemists should note that nitro-naphthalene is 
recommended as a "solvent" for india-rubber in 
preference to the nitro benzene hitherto generally 
employed. The author is to be congratulated 
npon a very useful contribution to a somewhat 
obscure and difficult branch of technical science. 
C. SWMONDS. 
—Nature, Feb. 5, 
