Digestion tube

The whole unit is accommodated in a fume cupboard fitted with a scrubber unit to remove the acidic fumes before emission to the atmosphere. The constructional materials of the fume cupboard should be able to withstand the heat radiated from the hotplate and heating blocks. A digestion tube containing a 350°C thermometer with the bulb embedded in a 2-cm layer of sand occupies one hole in each block. The hotplate can be connected to the power source via a time-switch, which can be set to come on approximately 1 hour before commencement of work this saves valuable time lost waiting for it to warm up. 

The most tedious aspect of the procedure is, after about an hour, to run a thin (4 mm diameter) glass rod vertically around the inside of the digestion tube in a downward spiralling motion in order to reintroduce any sample... 

After diluting the Kjeldahl digest to give a 50% aqueous solution, one observes a residue of silica and a fine white mineral deposit at the bottom of the digestion tube. There may also be some cloudiness in the solution, which should be left to settle for 48-72 hours. Using a disposable pasteur pipette, transfer sufficient of the upper clear solution to almost fill the autoanalyser sample cup. 

Does this mean that a hyperbeing could turn a human inside out From a practical standpoint, we re not quite as flexible as a rubber ball. We re also not spheres. We re more like a sphere with a digestive tube... 

The digestive tract from mouth to colon is often referred to as the digestive tube, whose biological and physical parameters are summarized in Table 3.1 (adapted from Daugherty and Mrsny 1999). In mammals, this tube has a four-layered... 

Aliquots containing 1-5 ig of phosphorus are transferred to digestions tubes, the solvent is evaporated in a fume hood, and digestion and assay are conducted as described in Chapter 3. Then the total phosphorus content of the sample coupled with the total weight value can give you a percent P value. 

The gastrointestinal barrier is considered to comprise two components the intrinsic barrier, composed of epithehal cells lining the digestive tube and the tight junctions that tie them together and the extrinsic barrier, consisting of secretions and other influences that are not physically part of the epithehum but which affect the epithelial cells and maintain their barrier function (Table 4.1). 

One general way to distinguish between various forms of symbiosis is to identify the location of the attachment of the symbiont to the host. Symbionts that live on the host surface, including internal surfaces like the digestive tube, participate in ectosymbiosis (Greek eictoc = outside). If a symbiont is localized within the tissues of the host, the association is termed "endosymbiosis" (Greek evSov = within). Endosymbionts can be found either in the extracellular space or intracellularly. 

Decomposition. A hemoglobin preparation (1.00 ml) is decomposed using 1 ml nitric acid (65%) and 0.5 ml hydrogen peroxide (30%). To prevent foaming three drops of octyl alcohol are added and the solution is carefully heated. A clear, light yellow solution is obtained, which is evaporated almost to dryness. To remove excess acid, 1-2 ml water is added and evaporated in vacuo at 90-100°C this is repeated once. The contents of the digestion tube are finally transferred to a volumetric flask and made up to 50 ml with water. 

Titration. After cooling, 10 ml water and 1 ml potassium thiocyanate (20%) are added. The titration with titanous chloride is carried out in the digestion tube in a COa atmosphere. The titanous chloride solution (about 0.15%) is frequently standardized against the ferric ammonium sulfate stock solution (mentioned in Section 2.1.2). 

Fig. 4.5 Scheme of the Tecator KjelTec semi-automatic distillation unit 1 for steam distillation of ammonia. (1) Condenser (2) receiver flask (3) alkali pump (4) splash head (5) digestion tube (6) steam valve (7) expansion vessel (8) steam generator (9) electrodes. (Courtesy of Tecator). 

Fig. 4.6 Tecator KjelTec Auto 1030 automatic analyser including distillation and photometric acid-base titration of ammonia. (1) Waste flask (2) water (inlet) valve (3) water aspirator (4) expansion vessel (5) feed valve (6) steam generator (7) vacuum valve (if tube drainage) (8) steam valve (9) water pump (10) digestion tube (11) alkali pump (12) distillation head (13) condenser (14) level pin (15) motor (stirrer) (16) lamp (titration vessel) (17) titration vessel (18) drain valve (titration vessel) (19) receiver solution pump (20) motor (burette) (21) burette cylinder (22) three-port valve (23) titrant storage flask. (Courtesy of Tecator).

Figure 2.5 Sea cucumbers have the capabihty of internal organ regeneration. Anatomy of the regenerating digestive tube in noneviscerated individuals of the sea cucumber H. glaberrima at different time points of regeneration. Source [34] Reproduced with permission from Elsevier...

An aliquot (20 ml) of a sample is added in the glass digestion tube, followed by the addition of 0.5 g of mercuric sulfate, 10 ml of dichromate solution, and 5 ml of sulfuric acid. The tube is placed into the microwave and connected to a condenser. An additional volume (25 ml) of sulfuric acid is added to the top of the condenser. The mixture is digested in the microwave at 150°C for 8 min. Excess dichromate in the digestion tube is determined with the standard titrimetric or colorimetric procedure. COD determination of real water and wastewater samples indicates that the results obtained from both microwave digestion and closed reflux digestion are consistent. 

Experiments show that there is no significant adsorption of cobalt on silica UV digestion tubes at the natural seawater pH or from acidified samples (Vega and van den Berg, 1997). There is therefore no need to acidify seawater prior to UV digestion. UV digestion has to be used to ensure complete release of cobalt from natural organic complexes as a small fraction of the cobalt tends to be non-labile. 

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