Suspensions, coarse

Coal (hard) and coke are used in water filtration, primarily for the removal of coarse suspensions, care being taken to prevent them from scouring or washing away, because of their relative lighmess and fine division. Coal is principally composed of carbon, and is inert to acids and alkalies. Its irregular shapes are advantageous at times over silica sand. 

Suspensions are conveniently divided into two broad classes—fine suspensions in which the particles are reasonably uniformly distributed in the liquid and coarse suspensions in which particles tend to travel predominantly in the bottom part of a... 

A colloid is a suspension of particles with diameters between 1 nm and 100 nm. The particles are charged and can be subjected to cataphoresis (electrophoresis). They are subject to Brownian movement and have a large amount of surface activity. Their properties lie between those of true solutions and coarse suspensions. 

A state of subdivision of matter with a particle size between 10"7 and 10 5 cm (1 nm to 100 nm). The properties of colloids lie between those of true solutions and coarse suspensions. 

A true solution consists of molecules or ions of a solid substance uniformly distributed throughout a liquid. A rubber solution is colloidal, i.e., intermediate between a true solution and a coarse suspension. Rubber solutions are used as adhesives and in the manufacture of rubber products by the dipping process. 

It is important to note that suspensions of fine particles tend to behave rather differently from coarse suspensions in that a high degree of flocculation may occur as a result of the very high specific surface of the particles. For this reason, fine and coarse suspensions are considered separately, and the factors giving rise to flocculation are discussed in Section 5.2.2. 

A solution of about 0.5 mol of allenylmagnesium bromide in -400 ml of Et20, prepared as described on p. 35, is cooled to - -40 C. The aldehyde (0.50 mol, freshly distilled, note 1) is then added dropwise over 20 min with vigorous stirring. After the addition, the temperature is allowed to rise from -40 to +10 C. In most cases a coarse suspension is formed. The reaction... 

A colloidal solution is regarded as an intermediate between a true solution and coarse suspension. 

Liquid ammonia (700-800 ml) is placed in the 2-1 flask. Stimng is started and 400 mg (note 1) of iron(m)nitrate (hydrate) is added, followed after an interval of 10 s by 2 to 4 g of sodium. As soon as the blue colour has disappeared, the remainder of the 1.0 mol of sodium is cut in to the grey to black solution (colloidal zerovalent Fe). The conversion into NaNH2 (compare ref.l) takes, as a rule, 25 to 30 min. The volume of the greyish, coarse suspension which has formed, is about 500 ml. Triphenylmethane (0.5 g) is added whereupon a reddish colour is developed. Acetylene (1 to 1.5 1/min) is introduced with efficient stimng. The suspension gradually disappears (note 2). The introduction of acetylene is stopped (removal of the inlet tube) when the red colour has disappeared. Sometimes the colour may reappear, in that case the introduction of acetylene is recontinued far a short time. 

Flocculation comes from the Latin word flocculate meaning loose and woolly. Flocculated systems result in rapid rate of settling because each individual unit is composed of many particles and is therefore larger. However, due to the loose packing of floes they are easily dispersible on shaking. Deflocculated systems on the other hand are made up of smaller particles whose settling rate is slower, but the settled particles tend to form an irreversible compact and are difficult to redisperse. This phenomenon is called caking. For coarse suspensions, a deflocculated suspension will have better uniformity of dose but poorer stability... 

Pharmaceutical suspensions are dispersions of solid particles in a suspending medium or vehicle (usually aqueous in nature). When the suspended solids are less than 1 pm, the system is referred to as a colloidal suspension. When the particle sizes are greater than about 1 pm, the system is called a coarse suspension. The practical upper limit for particles in a coarse suspension is approximately 50-75 pm. Depending on the affinity or interaction between the dispersed phase and the dispersion medium, a colloidal dispersion can be classified as lyophilic (hydrophilic) or lyophobic (hydrophobic). ... 

Lower layer contains brown coarse suspension of bran and aleurone cell walls... 

Here, is termed the fine relative viscosity and represents the contribution of the colloidal size particles. It is defined by the ratio of the apparent viscosity of the mixture of suspending liquid plus fine particles, to the viscosity of the suspending liquid, ju,. The quantity, is termed the coarse relative viscosity and is the contribution of the coarse particles to the net relative viscosity. It is defined by the ratio of the apparent viscosity of the coarse suspension, 17, to the apparent viscosity of the fine fraction, 17. ... 

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