IV. ESTUDIO TECNICO
1. DESCRIPCION DEL PRODUCTO
1.2 ORIGEN Y BOTANICA
V "i’’ ■- w;;;;;-..:;,.:/; .s>v»y,.y3: i ■■'•■• Z-.-A-^r.Pv/X >>*.■<
• ' ' ... ? ’ (1-87) ’ ' 1
peroxide’ was added to the sample while it is under a mechanical stirrer.
This was then placed in the oven for one hour at 40°C. Just before the
end of the time it was brought to boil to remove excesses ^0^. 800 ml. of deionized water was added to the mixture and it was left overnight to settle by gravity. Next day the clear liquid above the sediment cake is to be syphoned off and the sediment to be dried in the oven. After
drying, the sample was weighed and recorded in the sheet as the sample weight after treatment or the original sample weight.
Dispersion
Sodium hexameta,phosphate ’Calgon* was used as a dispersing agent in 10^ concentration. A standard volume of 20 ml. per 1 litre used to disperse the sediment where it had been left overnight to make sure that no flocculation occurs. Next morning, if no flocculation occurred, the mixture is ready for separation.
Sieving
The separation for the sieved size fraction and fine material is to be done by wet sieving through a 240 B.S. sieve. All fine particles washed through the sieve by deionised water are collected in a 1000 ml. graduated cylinder. The material retained on the 240 sieve was dried in the oven at 100°C. After breaking the lumps with fingers, the coarse fraction retained
on the 240 sieve was weighed and recorded as residue from wet sieving which is, in fact, original material weight for dry sieving. The difference in weight between the original sample and the residue from wet sieving is the
weight of material collected for pipette analysis. A/
(1-88)
A nest of new British standard sieves for dry sieving was built up in the following order of mesh sizes from top to bottom: 4, 8, 16, 30, 120, 240, and a lid and a receiver* The opening sizes of these sieves and their phi transformation for size diameter is shown in figures 31 - 34, and figures 41a ~ 45b.
The material retained on the 240 wet sieve was poured into the nest of sieves and shaken by the mechanical shaker for twelve minutes* The fraction retained on each sieve was brushed into a container and
then weighed to nearest 0.01 g. and recorded as material retained on that sieve*
The fine fraction which had been collected on the receiving pan was either added to the cylinder containing material from wet sieving, that was if the total weight of material passed through the 240 wet
sieve less than 2*5 g. Or it would be weighed and recorded as material passed through the 240 dry sieve, that is if the material collected in the cylinder from wet sieving was more than 2*5 g.
Pipette Analysis
A table based on Stoke* s lav; and Wadell’s formula had been
calculated to determine the particle sizes of the very fine materials in relation to the size of quartz grain specific gravity 2,6 at a
temperature of 20° C. A water bath with a thermo-stirrer was provided to/ .
(1-89)
to control the suspension temperature in the graduated cylinder. To enable an easy movement of the Andreason pipette over the water bath, the pipette was fitted to a carrier high enough to move over the six cylinders in the bath.
The first pipette withdrawal had. been taken 20 minutes immediately after stirring the suspension in the cylinder at the depth of 20 cm. from the top of the mixture. Stirring the suspension in the graduated cylinder, in the aquarium, was done by a stirring rod, a device described by Krumbien (1938 in: Krumbien & Petijohn 1938), Griffiths (1967), and Gatehouse (1971 in: Carver 1971)- The suspension stirred by inserting the rod into the cylinder and moving it up and down very rapidly for at least one minute.
As soon as the rod was withdrawn, the time was noted by stop-clock. 20 ml, of the homogeneous mixture in the graduated cylinder ready for analysissucked by a pipette at the fixed time and depth. The depth of the pipette into the suspension is controlled by a stand which will be described later. The material sucked through the pipette was, then, transferred into a 50 ml. evaporating dish and left to dry. The weight of the residue in the evaporating dish was determined by an analytical balance to nearest 0.001 g.
The procedure for weighing was as follows: each dish had been marked/
z a z'"-'5 J?;'.;*.r
(l~90)
marked, and weighed dry, then recorded as the weight of empty dish.
It was filled with the material in the pipette and weighed again when
it was dry. The weight of the empty dish was subtracted from the second weight to represent the weight of the residue in the dish.
The calculation of the particle size weight percent obtained by pipette analysis was done according to the following procedure. Since each graduated cylinder used for pipette analysis contains 2 g, of
sodium hexametaphosphate, it follows that each pipette withdrawal contains 0.004 g« of the dispersing agent. Subtracting this amount from the weight of residue in the evaporating dish will yield the total weight of the particular fraction in 20 ml. of suspension.
The 20 ml. of the mixture withdrawn by pipette is l/50 of the total volume in the graduated cylinder. The total weight of this particular withdrawal will be, therefore, found by multiplying the vzeight of the residue by 5^.
The material in the successive grades can then be found, by subtracting the weight obtained by the first pipette withdrawal from the total weight of fine material in the cylinder. The second pipette withdrawal from the first to obtain the next grade scale and the third
A
from the second and so on. These weights or the fractions of the successive grade scale could then be easily converted into percentages of the original sample weight. These percentages can then be used for cumulative percentages and curves as well as for the computation of the moment/
(1-91)
moment statistics. The results of the combined technique, sieving and pipette analysis, are finally expressed as the size distribution of the sample*
PART TWO THE ANALYSIS OP PEDIMENTS AND PAHS
PEDIMENTS
Definition
Terminology X
Pediments are the gently inclined degraded surfaces, with inclinations of not more than six degrees in most cases, and which are piedmont to mountain^
fronts. The half-planate surfaces of pediments are carved in hard rocks or in soft and loose rocks and they may be bare or veneered with thin fluvial and/or
proluvial materials. They are mostly found between mountain fronts and ,j valley or basin floors. They commonly form extensive bedrock surfaces
over which the products of erosion from the retreating mountain fronts are transported to the basins. McGee (1897) first used this term to describe a gently sloping plane carved out of hard rock below the steeper slopes of the mountain fronts.
Several American geomorphologists have contributed to the interpretation and definition of pediments after McGee. Among these are Davis (1930),
Blackwelder (1931), Johnson (1932), Rich (1935), Bryan (1936), Sharp (1940), Howard (1942), Tator (1952, 1953), Tuan (1959), Mammerickx (1964a, 1964b) and Denny (1967) • The process of pedimentation and the theories for pediment formation will be discussed later in this chapter. The point to raise here is the definition of pediments. Pour groups of pediments can be distinguished from the American literature. These are: proper pediments, dissected s pediments, buried pediments and coalescing pediments. But several authors have used the term pediment as a synonym of the German term (PussflHche) and ~
the French term (glacis).
The French geomorphologists have distinguished between the typical