Writing materials

Write material balances for the remaining two elements in the reaction equation... 

Leaves.—The leaves of some kinds of plants, after undergoing a process of drying and rubbing, make a tolerable kind of writing material. Mr. Herring says that the natives of India use them in preference to paper for ordinary correspondence, and even in important matters. This may arise from a strong attachment to old customs, and not from any alleged superiority in the material. So lately as fifty years ago a Persian manuscript was in existence, supposed to have boon written on some kind of leaves. 

Students will use paper and writing materials to draw colored lines that express particular emotions. 

Sampling schedule (Chapter 7), maps, and writing material. 

An atom is the smallest particle of an element that still retains the identity and properties of the element. For example, the smallest particle of the writing material in your pencil is a carbon atom. (Pencil lead is actually a substance called graphite. Graphite is a form of the element carbon.)... 

List the available data, establish a basis for the calculations, and assign letters for the unknown quantities. In many situations, such as in this example, some streams entering or leaving a process may have incomplete data to express their compositions or flow rates. The usual procedure is to write material balances as in the preceding examples but to assign letters to represent the unknown quantities. There must be one independent material balance written for each unknown in order to have a unique solution. 

Write material-balance and mole-fraction equations. A material-balance equation can be written for each element, based on the values found in steps 1 and 2. 

The most common microtraces examined in criminalistic laboratories are so-called contact traces (i.e. small fragments of paint coating, glass, single fibres, soil, writing materials). Moreover, traces of flammable liquids originating from fire debris or traces pointing to the use of firearms are revealed and identified. 

As a rule, chemical methods used in the examination of writing materials require initial preparation of a sample for study. Paper chromatography, thin-layer chromatography and capillary electrophoresis are experimental techniques often applied. These methods lead primarily to separation of the dyes contained in the ink under examination and to the discrimination of ink samples. The techniques are simple to use, require a small amount of sample for examination, are selective and give reproducible results. Their basic disadvantage, however, is the necessity to isolate the ink from the substrate (e.g. paper) on which the examined document has been prepared. Solvent extraction of the ink often leads to partial damage of the document. 

Part Two of this book, which begins with this chapter, outlines procedures for writing material balances on individual process units and multiple-unit processes. In this chapter we present methods for organizing known information about process variables, setting up material balance equations, and solving these equations for unknown variables. In Chapters 5 and 6 we introduce various physical properties and laws that govern the behavior of process materials and indicate how these properties and laws are taken into account (as they must be) in formulating material balances. 

Chemical processes may be classified as batch, coatinuous, or semibatch and as either steady-state or transient. Before writing material balances for a process system, you must know into which of these categories the process falls. 

The product gas that leaves a combustion furnace is referred to as the stack gas or flue gas. When the flow rate of a gas in a stack is measured, it is the total flow rate of the gas including water on the other hand, common techniques for analyzing stack gases provide compositions on a dry basis. You must therefore be able to convert a composition on a dry basis to its corresponding composition on a wet basis before writing material balances on the combustion reactor. Hie procedure to convert a composition from one basis to another is similar to the one used to convert mass fractions to mole fractions and vice versa given in Chapter 3 assume an amount of the stack gas (e.g., 100 mol of wet gas if composition on a wet basis is known or 100 mol of dry gas if a dry basis composition is known), calculate how much of each component is present, and use this information to calculate mole fractions on the desired basis. 

Given an adiabatic process or any other nonreactive process for which the value of Q (closed system) or Q (open system) is specified, write material and energy balance equations and solve them simultaneously for requested quantities. 

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