September i, 1887.] THE TROPICAL AGRICULTURIST. 
185 
EXPORTS AND ESTIMATES OE TEA. 
A leading member of the planting community 
writes : — 
"My last Loudon news re produce is : — Plantation is 
selling readily at 96s to D8s for middling to good 
middling. All kinds of tea of distinctive character, 
whether China, India or Ceylon, are in good demand 
at firm to higher prices, but the ordinary colourless 
Ceylon are slow of sale and irregular. 
" Don't you think Rutherford's estimate in Forbes 
& Walker's report of 1887-88 crop (tea) too high ? It 
will not bo much more than 12,000,000 lb. in 1886-87. 
From 12,000,000 to 22,550,000 is rather a jump, es- 
pecially as men will try to make letter tea, which 
means finer plucking." 
Our correspondent's question represents the feeling 
with which we read the estimate referred to. Mr. 
Eutherford has so carefully examined the statistics 
of tea and is generally so cautious, that we feel 
diffident in questioning his figures, but certainly 
the jump from 12 millions of pounds in 1886-87 
to very nearly double that quantity in 1887-88 
does seem somewhat to approach the " prodigious." 
The estimated increase partakes more of geo- 
metrical progression than of ordinary arithmetical 
advance. The figures may, nevertheless, be reached, 
if there is now a reaction to weather favourable 
to flushing from the very unseasonable meteoro- 
logical conditions which tea planters have had to 
contend with for months past. Notwithstanding such 
adverse influences, we have exported to date about 
10£ millions of pounds, so that by 30th September 
it seems probable the round figure ef 12 
millions will be quite made up. Then will come 
in October to January, what are reckoned 
the best flushing months, over a large number 
of the districts in which mature tea is largely 
grown, and unless we are visited by a third 
visitation of drought and cold, the tea harvest ought 
to be good. On the whole, looking at the fact that 
the reality this season will be about one million 
of pounds below the estimate, we should think 
20 millions a safer figure for the year which 
will commence on 1st Oot. than 22i millions. But 
there are too many elements of doubt in the 
question to render prophesying safe until after 
the event. A general resort to finer plucking, 
which has been pressed on the planters would 
doubtless rostrict the quantity manufactued, but 
having stated these possibly qualifying conditions 
we must leave our readers to form their own 
judgment. 
♦ 
IMPORTANT CHEMICAL DISCOVERY: 
CONCRETE AS AFFECTED BY SEA- WATER. 
Some time ago the Scotsman drew attention to an 
interesting discover}' that had been made in connection 
with the Aberdeen harbour sea-works, and the experi- 
ments that have since been carried on will have a very 
important bearing in the building of similar structures 
throughout the country, and, indeed, in every part of 
the world. Engineers and architects have hitherto 
regarded Portland cement concrete, which has been 
almost exclusively employed in the construction of 
harbour, dock, and other works, as almost infallible. 
After the lapso of a certain period, however, from the 
completion of their work, engineers are now being fre- 
quently discouraged to find that their best efforts to 
secure good material and workmanship have been 
seriously operated against by indications of failure 
where this valuable cementing material is depeufded 
upon to perform ono of the chief functions iu the 
execution of extensivo and costly undertakings of the 
kind alluded to. Although its effect was suspected 1 , the 
nature of the chemical action of sea water on cement 
has never been thoroughly investigated; and this is 
therefore the first experiment that has really resulted 
in what promises to bo a successful explanation of the 
deleterious substances that bavo up till the present 
moment baffled the skill of the analyst. The destruct 
tiou of enormous concrete blocks and concrete walls ae 
Aberdeen has usually been ascribed to the force of th" 
sea and other mechanical inHuences. The " decayed 
concrete, however, is first swept away, and ohemical 
action did not become so noticeable at the pier as it was 
in the graving dock in still water. Where the quay- 
walls have stood in still water without pressure, this 
process has been comparatively slow and insignificant. 
It is the action of the sea-water under pressure, in still 
water, that has rendered the nature of the damage in 
the present instance so conspicuous. Similar effects 
have recently been observed at the entrance to other 
graving docks — for instance, at Maryport, the Walter 
Scott Dock, Newcastle-on-Tyne, and elsewhere. The 
decay of the concrete of sea-works may now, however, 
be accounted for, in view of the light thrown upon the 
subject by Professor Brazier, of Aberdeen University, 
in conjunction with Mr. William Smith, the harbour 
engineer. 
Since its construction some fifteen years ago, one of 
the destructive influences bearing on the south break- 
water has evidently been the disintegration of the 
surface of the concrete by the chemical action of the 
salt water on the Portland cement. A similar effect, 
but on a larger scale, has also been manifesting itself 
on the graving dock, which was completed two years 
ago. The entrance walls are built of Portland cement 
concrete, composed of one measure of cement, two 
measures of sand, and three measures of stones, with 
large rubble stones incorporated iu the walls. The 
surface of the walls, from the foundation up to a level 
of three feet of low water, is plastered with Portland 
cement mortar, made up of one measure of Portland 
cement and one measure of sand. The upper part of 
the wall is faced with granite ashlar stones, surmounted 
by a massive granite cope. Portland cement plaster 
was supposed to be sufficiently watertight to a form a 
sound, hard skin on the concrete walls. It appears, how- 
ever, that the process of emptying the water from the 
graving dock, when it is occupied by ships, places a hy- 
draulic pressure, varying with the tides, of from 5 lb 
to 11 lb. on the square inch on this concrete skin. The 
sea water, forcing its way freely through the small pores 
in the skin, has saturated the quay wall. The presence 
of sea water has occasioned a swelling due to the chem- 
ical change produced by the water, which in its turn 
opened up the skin in a series of larger cracks, allow- 
ing access to a greater volume, so that the chemical 
action proceeded more quickly the longer it lasted. The 
pressure of water being relieved from the surface of 
the entrance wall, which is within the caisson gate, 
flows through the pores of the upper part and out into 
the dock through the cracks in the skin of the inner 
part, the whole of the entrance walls in the neighbour- 
hood of the caisson haviug expanded about 2| inches 
on the height of the walls. The chemical change is 
hastened the longer the exposure continues ; it is in- 
creased by the perpetual passage of the current of sea 
water through the body of the concrete. To this must 
be ascribed the rapidity of the chemical ac' ion in this 
case beyond what is generally observed in concrete 
worksundersea water. The injury to the dock-gate 
entrance walls was first observed from the opening of 
the joints of the ashlar facing at the south-east corner. 
It was found that the surface of the concrete at this 
point immediately beneath the ashlar had loosened, al- 
lowing the ashlar to drop slightly. The concrete be- 
hind the ashlar under high-water mark bad also loosened 
thus breaking the bond of the stones with the con- 
crete. The damage so far to the walls is found to he 
superficial iu extent, and it is believed that a new facing 
of granite built in Portland cement mortar will be 
effectual iu preventing the extension of the chemical ac- 
tion On the discovery of the softening of the Port- 
bind cement concrete, the engineer consulted Prof esj i 
Brazier as to the composition of the decayed concretes. 
T.st briquettes were submitted for analysis. Some ot 
tho briquettes were broken dining the course ot the 
work, and found to be lully up to the mechanical stand - 
ard The chemical analysis was made with the view ot 
diseuvering the proportion of magnesia tbeso con- 
tained, the preseuceof magnesia being supposed to 
