Thimble volume

Flow rate 4 ml/min mass flow of liquid CO2 at the pump. Thimble volumes 10 Thimble size 1.5 ml. 

Step II. Next, the same SFE extractions were rerun using the same flow rates and thimble volumes as for step I, but at a chamber temperature of 80 °C. The same densities were used except that 0.8 g/ml was substituted for 0.95 g/ml at the new temperature. The density of 0.8 g/ml at 80 °C was used because of the upper pressure limit of the extractor. The upper pressure limit of the extractor was 400 atm., therefore at 80 °C, this corresponds to a density of 0.80 g/ml for C02. In this case, the extracts collected at 0.6 and 0.8 g/ml densities were... 

Thimble Volumes. To properly compare extractions while changing the density, the number of thimble volumes swept was kept constant for all extraction steps. In this case the extraction time was changed as a new density setpoint was chosen for each extraction step while the flow rate at the pump head was kept constant. The pump head is where the flow of liquid CO2 is controlled. Control of the liquid C02 controls the mass flow of the system. As the density and the extraction times changed, so did the mass of C02 used per step however, the net volume of solvent seen by the sample did not change. Importantly, as the solvent changed from 0.25 g/ml C02 to a solvent of 0.95 g/ml C02, more C02 was required to displace the same volume element. Since the mass flow was held constant in this set of experiments the extraction time had to be changed to normalize for equivalent volumes of solvent as seen by the sample. 

Thimble Volumes. For these experiments the thimble volumes and the extraction times were held constant. To accomplish this, the mass flow of the system had to be varied by changing the flow rate at the pump head for each density step. Controlling the mass flow rate allowed the linear/volumetric flow to be consistent throughout the experiments. This is different from the paprika experiments in which the mass flow was held constant and the extraction times were changed, to keep thimble volumes constant for each extraction step. Flow control is one of the major advantages of variable restrictor based SFE units. 

Modifiers were selected for addition to the spiked soil samples representing a range of solvent polarities. Based on the results of the density stepping experiments, the extraction times were increased to 19 minutes from 9.4 minutes, which increased the thimble volumes from 5 to 10. To be consistent throughout the experiments, 1 ml of modifier was added directly to each extraction cell. Methylene chloride was chosen as a non-polar modifier. Results show that the methylene chloride did little to aid in the extraction process for any herbicide. 

Sample Contact with As sample fills more of the thimble, remember to incorporate that In considering thimble-volumes-Exlraction Fluid swept. 

Many continuous extractions involving solid samples are carried out with a Soxhiet extractor (Figure 7.18). The extracting solvent is placed in the lower reservoir and heated to its boiling point. Solvent in the vapor phase moves upward through the tube on the left side of the apparatus to the condenser where it condenses back to the liquid state. The solvent then passes through the sample, which is held in a porous cellulose filter thimble, collecting in the upper reservoir. When the volume of solvent in the upper reservoir reaches the upper bend of the return tube, the solvent and any extracted components are siphoned back to the lower reservoir. Over time, the concentration of the extracted component in the lower reservoir increases. 

The boiler is made separately. The inner tube is chosen to fit the heater to be used, and the outer tube is of such size that the annular space has a volume of 30-40 c.c. to just above the top of the inner thimble. A boiler holding more mercury can also be used. 

The classical Soxhlet extraction technique has seen some improvements, mainly in the submersion of the whole extraction thimble into the boiling extraction solvent, degree of automation, and in reduction of solvent volume. In a recently introduced universal extraction system (Biichi) four SLE methods are contained in one device Soxhlet Standard, Soxhlet warm, hot extraction and continuous flow. It is possible to use solvents with boiling points of up to 150 °C inert gas can be supplied during the extraction process. 

The solid is transferred to a Soxhlet thimble (45 X 125 cm.) con-laining a 5-cm. layer of anhydrous sodium carbonate on the bottom (Note 6), and the solid is extracted for 2 to 3 hours with anhydrous cl her (700-800 ml.). The total volume of ether is brought to 800-900 ml. The ethereal solution is treated with charcoal and boiled for 10-15 minutes under reflux then the solution is filtered by suction (Note 7). After evaporation of solvent, 30-33 g. (35-38%) of white 2-chloro-iiirotinonitrile is obtained, m.p. 105-106° (Note 8). 

For further purification the crystallised acid is boiled for a quarter of an hour under reflux with methylated spirit (one part by volume of spirit for each part by weight of acid), left over night without filtering, then collected again at the pump, washed with alcohol, and finally the almost colourless material is recrystallised from spirit, in which it is dissolved by boiling under reflux. The pure cholic acid separates on cooling in the form of transparent tetrahedral crystals. Melting point 196°. A further quantity of pure substance can be obtained from the mother liquor by concentration. If the acid, partially purified as described, is extracted in a thimble with ethyl acetate, a very fine preparation is obtained. The yield of pure acid amounts to fully 50 g. 

Each run was continued for about 25-30 hours, and about 25 liquid samples were taken during this time. The volume of each sample was between 15 and 30 cc. Samples taken in each run were treated similarly. They were transferred into Soxhlet thimbles which had already been dried for Vz hour. The thimbles were placed in the Soxhlet extraction unit using benzene as the solvent. The extraction was continued until the liquid circulating in the unit became clear and colorless (indicating pure benzene). 

Modifier Addition Using Premixed Cylinders. The use of pre-mixed modifiers and C02 was also investigated. A 5% by weight mixture of isopropyl alcohol and C02, and a 7% by weight mixture of methylene chloride and C02, were used under the same extraction conditions. These mixtures represent approximately a 4 mole % mix of each modifier with C02. Under these extraction conditions this corresponds to 3.6 - 4.4 ml of liquid modifier being used per extraction instead of the 1.0 ml volume added directly to the extraction thimble. The recoveries... 

The residence time is calculated based on the fluidizing gas velocity, assuming that the "free volume" (i.e. the volume of the expanded bed minus the volume of the sand) is fully utilized. At the temperature, total reactor gas flow rates, and sand bed volumes used, the residence time was about 0.5-1.0 sec. A typical operation began by washing the sand in 10% HNO3 and distilled water to remove impurities, such as iron, which may act as catalysts, and then calcined at 850° C for at least 12 hours to remove any sulfides and carbonates. The coal feed is then begun and pyrolysis products then exit the pyrolyser to a set of two cold traps fitted with cellulosic thimble filters maintained at 0° C. The outlet gas temperature after the first trap is 30-34° C. Much of the light char formed is entrained in the exit gas and carried into these traps, with most of it in the first trap. 

When we talk about black holes, I ll tell you more about the density of stars. For now, realize that the Sun is actually only slightly more dense than water. Because red giants have about the same mass as the Sun in a huge volume, their average densities are very low—about the same as that of vacuums produced on Earth. On the other hand, consider the white dwarfs. These are faint stars that are the evolutionary endpoints of intermediate- and low-mass stars. A majority of stars, like our Sun, end their lives as white dwarfs. If I were to give you a thimble full of white dwarf mass, you could never lift it. A teaspoon of white dwarf material weighs several tons on Earth. The time needed for a white dwarf to cool down is billions of years. ... 

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