attached to the process are generally not sufficiently appreciated. In this pale rubber minor blemishes are so plainly apparent that their i

ng too harshly the occasional lapses of an estate struggling to give of its best to the market. At the same time there can be no doubt that if precautions are taken to attend to all likely sources of cont

e trend of the argument in its favour. It will be recognised that the necessity for standardisation exists to the same degree in the correct preparation of pale cr

all fields or divisions are fairly uniform, and of high rubber content, the standard may be taken at a figure equivalent, for example, t

of the cut on the tree, general health of the tree, etc. On a rainy day the

ve even approximately correct readings in

er working on the machines, less labo

des of Cr

crepe; second quality p

t found suitable for sheet rubber should be taken-viz., 11?2 lbs. dry rubber

fected in the ordinary "Shanghai" glazed earthenware jars containing about 45 gallons. Given reasonable care, and a

hing

anks in the background, and then sc

hould be installed. Where both sheet rubber and fine crepe are being prepared, the whole system of sheet

size suitable for the machines. The knives or saws are sometimes rusty, and the colour of the coagulum is affected. The coolies ofte

m is obviated. The long strips are handled and fed into the rolls easil

e recommended that for latex standardised to a level of 11?2 lbs. per gallon, the proportion of pure acetic acid should be in the ratio of 1

f acetic acid required, should be taken on the ratio 1:1,000. Where latex exceeds a dry rubbe

tisfaction, and the quantity of acid solution must be increased slightly in order to obtain complete coagulation.

acid to 100 parts water

per gallon. 2

s of standardised latex. Of the above solution use 1

ning all cases, as so much depends upon the treatmen

e preparation. While such solutions may be effectively stirred in when the latex is dilute

of less than three hours, an excess of acid must be employed. The excess need be comparatively small, unless the interval is much reduced. For instance, it is the practice on some few estates to begin the machining of the coagulum about half an hour after coagulation commences; in which case it is usual to add from a quart

direct traffic between producer and consumer, it must be recognised that in the vast majority of cases we are forced to concern ourselves only with the standards set up in the markets. This, in spite of the knowledge th

bisulphite as the agent for the prevention of that da

s in (b) of that formula may be increased slightly, and the exact requirements found by experience. The caution must again be given that the employment of an excess of sodium bisulphite will lead to the production

d latex. Many estates will find it expedient to use less of the chemical; and if it is found that the desired result i

sulphite are both bought for our purpose in the form of a fine crystalline powder, and on analysis

of complaints or enquiries reaching the laboratories. To the layman, and certainly to the native who usually has charge of these substances, it is not a simple matter to distinguish between them without special knowledge. There are certain elementary tests, however, which can be applied on al

ere can be no question that it is to the interests of chemical manufacturers to supply the best article; and i

lphite. Sod

owerful odour of sulphur dioxide.[

litmus-paper red. 2. In solution it

um is allowed to remain open. 3. The tendency to "ca

e estate, and as a result of short exposure to the moist atmosphere of the tropics, a

r effective as an anti-oxidant and disinfectant. It is within the experience of all accustomed to the handling of this chemical, that in addition to the loss of gas, the powder cakes into a hard mass on exposure. If only

ing its treatment in storage. It should be bought only in drums (or other air-tight containers), and should be stored in a dry place.

bvious that, although the prime cost may be cheaper with the larger quantity, it would

asis of a maximum of 1 lb. per 100 gallons of latex. A 56 lb. drum, assuming no loss or waste, should be sufficient to treat at least 5,600 gallons

mical when a drum is opened. It might be of advantage to place the contents of the drum in smaller sealed tins, or to have m

upon the necessity for care in the preparation of the solution. Equa

ution of acid, with stirring. Obviously this led at least to a great los

of solution and latex should be thoroughly stirred, and if only natives are in charge a minimum period of five minutes s

e deficiency will most probably be manifested in the dry

n an effect double the quantity may be required, and the residual salts left in the rubber on evaporation

entioned that previous to the introduction of sodium bisulphite pale crepes were made in

ve quantities of s

tex in conjunction with ex

conjunction with steam

ction with excess of acid and subsequen

of a mineral acid su

ry dilute latex, coagula

y machinery for crepe-making is relegated to Section III. of

y is necessary, and ample engine-power must be av

nt speeds, as to have a macerating effect upon the coagulum

ined from the macerators into a form suitable for passing to the rolls described in (c). They are sometimes called "c

peeds and, as their name denotes, devoid of any groo

crepe." In the common acceptation of this term crepe of No. 1 quality generally connotes fin

ates, but the "finish" will be that typical of the particular grooving of the intermediate rol

from the coagulum is now very uncommon. Thick crepes are generally made by reworking dry rubber, either in the form of thin crepes or from air-dried s

ecessitates this thin crepe being of even texture and fairly free from small holes ("looseness"). What difference the small holes are to make in th

t be passed consecutively through the three types of r

this is possible on all estates. Clearly the number of times the rubber passes through the rolls will depend upon the total efficiency of the machines. This in turn involves such factors as (a) the size of the rolls, (b) the number of machines of

on of the rubber; and this has been confirmed by others.[10] Apart from this point, it should be recognised that over-workin

M.S., April, 1918, "Preparation and Vulcanisation

tate to discover the minimum number of times which rubber should pass through the machines, consistent with the factors indicated above. In any case it may be assumed that if any factory cannot p

It has since been recognised in some measure that no reason exists for such a wide difference in price, and more recently the margin between even the first-grade rubber and the lowest grade of scrap rubber has been a gradually diminishing one. Providing sufficient care is exercised in the preparation of the lower grades, one would expect to see but very

colour, due to the fact that the lumps oxidise very quickly. When they are allowed to remain overnight before being machined, it can be imagined that

t-grade crepes should be very slight. Too often, however, not sufficient supervision is given to the coagulated-lump rubber, and it is common to see it come into the factory cont

solution is sufficiently powerful. It is not to be thought for a moment that by the use of sodium bisulphite any previous oxidation will be counteracted; all that is claimed for the treatment is that any further surface oxidation will be checked, and the rubber may be allowed to remain until the next day, for working, if it is so desired. It will probably be found that quite a quantity of latex has been expressed from the lumps by contraction, and acid may be added to obtai

find it possible to prepare from naturally coagulated

es as a second quality of smoked sheet; but generally they are amalgamated with the rinsi

e, represent a very dilute latex, the rubber

f water poured into the first bucket, and this dilute latex used progressively in all the buckets of that gang of tappers. The result is a fair latex which can be added to the bulk of No. 1 latex, provided it is free from dir

will be understood that if trees are not regularly "scrapped," there is a danger that the crepes may be found to contain tacky streaks due to the inclusion of old scrap which has been sun-baked

is paid for per pound collected, it is usually the rule to insist that scrap shall be washed free from dirt and picked free of bark. This course is to be commended, but might proba

of uniform colour is to be obtained these dark scraps must be rejected, otherwise dark streaks wil

ection that the method of obtaining and collecting b

unt of rubber to be extracted from the dry shavings is very small-so small, in fact, that whe

rubber derived from the mixture may be 30 to 40 per cent. upon the gross weight-depending chiefly upon the quality of the tapping (i.e., in

ss the factory is equipped with a special "scrap-washer" it is advised that this material should be sent for working to a

owed to stand about for a day or days. Is it any wonder then that tackiness was found to develop when the rubber was dry? It is here definitely laid dow

ably these old pieces have been exposed to the sun for days, and have become quite resinous. It would be practically impossible to go through all earth-scrap in order to find these odd pieces, but unless this were

of cloth or cotton-waste are concealed. Coolies may have used them for cleaning cups, or the store coolies ma

atment of lower grade rubbers. In these the raw rubber is well mastic

"U.E." scrap-washer, made by the United Engineering Company (Singapore), gives very good service. The "C.C.C." washer, made by the Colombo Commercial Company, is suitable for the purposes of an average estate. There are others, less well known.

e to state the ordinary speed of the back-shaft, length of drive, etc. It does not follow that the larger the rate of output, the greater is the eff

was not uncommon to find superintendents innocent of the fact that a certain type of washer possessed movable parts upon which the efficiency of the cleansing largely de

s of iron, spouts, etc., which are sometimes present in the loose scraps of rubber or shavings, owing to the carelessness of coolies. Under the best regulated-system,

y it often contains a quantity of internal or adhering earth. Before entering the washer a good proportion of the external soil could be removed if the scraps w

the cold water supply) for an interval during the working of each charge. Where possible, such instructions should be followed, as by this means the individual

of lower grade rubbers appears to be changing. In the past, from any one estate th

d) obtained from coagulation of

tained by coagulation of the skimming

ed from naturally-coagulated clots fo

from scrap which had coagulated

ade by maceration of bark-shavings t

f the trees. As it is often a matter of weeks between any two regular collections, it is easy

bewildering. There appeared to be a regrettable lack of uniformity, even in the appearance of, say, a bark scrap rubber from any two estates. When, in addition to these variation

hould be pointed out that within certain limits the trouble continu

rrect to state that what a manufacturer requires is a big "parcel" uniform in appearance and treatment, even though the colour may not be so light as that of many

hade of colour of this compound crepe will depend largely upon the types of rubber employed, but as a rule it is somewhat darker than the highest of the types employed in the mixture. To the writers this seems immaterial as long as the manufacturer is offered a larger and more uni

y coagulated

ree-s

-shaving

or (b) and (c). Now, as a general rule, the actual percentage of crop made into (b) is appreciably less than that made into (c) and still less than (b) and (c) together. Apparently, therefore, there would be a margin of profit on the

attempt to make a compound crepe containing that type of rubber, as one would run the risk of spoiling the whole. It seems certain that in course of time a scrap-washer will be considered as necessary a piece of machinery as an ordinary crepeing machine in the facto

n advocated, and it is gratifying to find that in many cases the amending grades sugg

latex coagulat

. 2. C

3. Earth

any compound crepe, as the risk of possible "tackiness" in the whole would be serious. In the case of the bark-shavings rubber to be incorporated, it is first cleaned alone in

nly three grades, there are

latex coagulat

washings, etc., skimmings, a

from tree-scrap and

4. Ear

, and they all conduce to simplification of working, and a

great mistake. With the exception of the lowest grade (earth-rubber), it would not be unfair to state that the quality of the rubbers on testing should be very little inferior to the No. 1 product. Often, as in the case of naturally coagulated rubbers, they are superior in some respects to ordinary fine pale crepe. Doubtless manufacturers are a

, and "blanket" crepes. More often than otherwise, the medium and thicker crepes are prepared direct in those forms. It follows that they are liable to attacks of "spot" disease, which,

to remain on racks overnight before blocking. In other instances, the sticky rubber from the vacuum drier is passed once or twice through wet, smooth rolls and hung to dry for some days. The dry crepe is then folded into the pressing box or cut to suit the size of the box. Pressure is applied for some time, and finally the rubber is taken ou

ecessary to point out that essentially block rubber is merely pressed crepe rubber. It is inconceivable th

packing, and a saving in freight; but there is the disadvantage, from the consumer's poin

robably all which is put into the market is really comprised of (1) clippings obtained from the ends of shee

These show signs of contained moisture when the bulk of the sheet is perfectly dry, and as undue delay would ot

om the smoke-house, may be made into crepe, rather than it should

ence upon the quality of the rubber on vulcanisation

o the best smoked sheet for manufacturing purposes, but owing to the prevailing system of e

nd shipped as "sheet clippings" or "sheet trimmings"-a procedure which would appear to be justified by a steady demand. In