Parchment membranes

By itself a subject of study, metallic yam used in the past comes in a number of varieties that reflect the level of technology and trade of the time. A majority of metallic threads has been made into yarn by cutting prepared metallic material into strips that were then wound around a core thread of silk or linen. The metallic materials used were either gold or silver leaf adhered to membrane, parchment, leather, or paper or plain soft metal. Membrane is adversely affected by water and... 

In contrast to mechanics, where the term membrane (Lat. membrana = parchment) designates an elastic, two-dimensional plate, this term is used in chemistry, biophysics and biology to designate a solid or liquid phase (usually, but not always, with a thickness substantially smaller than its other dimensions) separating two, usually liquid, phases. The transport (permeation) of the various components of both phases through the membrane occurs at different rates relative to those in the homogeneous phases with which the membrane is in contact. The membrane is consequently called semipermeable. 

In physics, an elastic two-dimensional plate is tenned a membrane (Latin membram = parchment) but in chemistry the tenn denotes a body, usually thin, which serves as a phase separating two other bulk phases. If this body is penneable to the same degree for all components of the adjacent phases and does not affect their mobility, then its only function is to prevent rapid mixing of the two phases. This is then tenned a diaphragm. A real membrane must exhibit a certain selectivity, based on different penneability for the components of the two phases, and is then tenned a semipenneable membrane. Membranes separating two electrolytes that are not penneable to the same degree for all ions are called electrochemical membranes. It is with these that we are concerned here. 

CA 24, 3726(1930) to apply to analysis of an alloy in which the metal to be determined is deposited on a Pt electrode without the application of any outside electrical current. Instead, an anode of the baser metal in the aiioy is placed in contact with the solution containing its ions in a compartment separated by a parchment membrane from the solution to be examined... 

Thomas Graham s investigations of diffusion 11861) led hun to characterize as crystalloids substances, such as inorganic salts which in water solutions would diffuse through a parchment membrane and as colloids... 

When a solution of ferric chloride is poured into a relatively large volume of boiling water, colloidal ferric hydruxide is furmed The ferric hydroxide sol does nol react with hydrogen sulfide nor with potassium hcxacyanoferralc(ll), and like all colloidal substances does nol pass readily through animal membranes or parchment. 

An apparatus lor carrying out a dialysis usually consists of two chambers separated by a semipermeable membrane of parchment paper latex, animal lissue. or oilier colloid. In one chamber the solution is placed, and in Ihc other, the pure solvent. Crystalline substances diffuse from the solution through the membrane and into the solvent much more rapidly than amorphous substances, colloids or large molecules. 

Dialysis The purification of colloidal solution by this method is based on the inability of the sol particles to pass through an animal membrane or a parchment paper which allows only the molecules or the ions to pass through. The vessel in which dialysis is carried out is known as dialyser [Fig. (2)]. A dialyser consists of a special type of vessel open at both the ends. To the lower end a membrane is stretched. This membrane allows only the solvent and other molecules to pass through it, but it is impermeable to the colloidal particles. The dialyser is then suspended in a larger vessel... 

The tamarind fruit (pod) has mainly pulp and seeds. The seeds are covered by a thin parchment, membrane-like structure. The pulp constitutes 30-50% of ripe fruit (Purseglove, 1987 Shankaracharya, 1998). The shell and fibre account for 11-30% and the seed constitutes around 25 10% (Chapman, 1984). The fruit pulp (both ripe and dried) contains mainly tartaric acid, reducing sugars, pectin, tannin, fibre and cellulose. The general composition of tamarind fruits is given in Table 20.1. 

Another procedure for determining the net amount of water transported during electrolysis is to separate the anode and cathode compartments by means of a parchment membrane and to measure the change... 

Physico-Chemical Properties of Salvarsan Solutions.— These solutions show the characteristic properties of colloids, dialysis through a parchment membrane showing but slight diffusion, w hiist in methyl alcohol solution diffusion takes place more readily. The disodium salt diffuses about four times as quickly as the free hydrochloride. Hie idscosity of aqueous solutions of Salvarsan increases from the moment of preparation until an approximately constant value is reached. This value is much higher than the initial value. As the concentration of the solution increases, the initial velocity of increase of scosity and the final value are affected, and the presence of acid or alkali also has a marked effect. With rise of temperature the viscosity more quickly attains its maximum value, but this value is diminished The viscosity of dilute solutions diminishes on keeping. The ps value of Salvarsan is 7-60 of the dihydrochloride, 2-41 of the monohydrochloride, 3-00 of the monosodium salt, 10-88 and of tlie disodium salt, 11 43. The presence of an isoelectric point at ps value about 3 4 is indicated. ... 

The fruit (Figure 1) contains about 55% pulp, 34% seeds, and 11% shell (pod) and fibers (Rao and Srivastava, 1974, cited in (77)). Pods contain 1-10 seeds, which are irregularly shaped, flattened or rhomboid. Seeds are very hard, shiny, reddish, or purplish brown. They are embedded in the pulp, lined with a tough parchment resembling a membrane, and joined to each other with tough fibers (Purseglove, 1987, cited in (77)). There are great differences and variations in fruit size and flavour (77). 

The colorimetric method fails in solutions which are very darkly colored or extremely turbid. Frequently this difficulty may be overcome by the dialysis method, especially when the colored substance is colloidal. The investigated solution is placed in a thimble of pure parchment or in a collodion membrane set in a little pure water. After it has been ascertained that the pH of the external water no longer varies, its acidity is measured colori-metrically. The time required is usually twelve hours or less, and must be determined for each case. The author has obtained good results by this method when used to measure the pH of soil extracts, milk, emulsions, etc. 

The fruit is, when ripe, a red drupe containing white seeds, the seed coat of which has a thin parchment-hke membrane, which is called silver membrane. The seed consists mainly of endosperm. The coffee-bean consists of the peeled seed, which is roasted at a temperature of 200-250°C, when the caffeine is partly sublimated, and the aromatic substances are formed. 

The C-substance is non-toxic in mice, in amounts up to 1 mg., and appears to be a smaller molecule than the type-specific polysaccharide, since it passes through collodion and parchment membranes. ... 

Membranes suitable for dialysis include vegetable parchment, animal parchment, gold beater s skin (peritoneal membrane of cattle), fish bladders, collodion and cellophane. 

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