2. Lead in. Work with the text.

1. Match the words with the definitions

1. analysis	a. the measurement of weight, gravitational field, or den­sity
2. synthesis	b. an instrument or devicc for determining and specify­ing colors
3. precipita­tion	c. the production of a substance by a combination of chemical elements, groups, or simpler compounds
4. blowpipe	d. the process of forming a substance separated from a solution or suspension by chemical or physical change usually as an insoluble amorphous or crystalline solid
5. spectro­scopy	c. the producing of chemical changes by passage of an electric current through an electrolyte
6, electrolysis	f. the identification or separation of ingredients of a sub­stance
7. specific gravity	g. the process or technique of using an instrument for forming and examining spectra especially in the visible region of the electromagnetic spectrum
8. titration	h. the ratio of the density of a substance to the density of some substance (e.g. pure water) taken as a standard when both densities arc obtained by weighing in air
9. combustion	i. a small tubular instrument for directing a stream of air or other gas into a flame so as to concentrate and in­crease the heat
10. gravimetry	j. an act or an instance of burning
11. conduc- tometry	k. a method or a process of determining the concentra­tion of a dissolved substance in terms of the smallest amount of a reagent of known concentration required to bring about a given effect in a reaction with a known volume of the lest solution
12. colori­meter	1. an instrument used for observing the internal structure of an opaque objcct (as a living body) by means of X-rays
13. fluoro- scope	m. titration based on determination of chungcs in the elcctrical conductivity of the solution

3. Read and translate the text.

Chemical Analysis

As you know, chemistry is the study of different kinds of matter, called substances, and the changes involved when one substance is transformed into another. Matter exists in three different states: solid, liquid and gaseous.

The most important characteristic of a substance is its uniformity of composition and the fact that all samples of a specific substance show the same properties. There are two kinds of properties: physical (color, taste, odor, touch, density, hardness, solubility and ability to conduct electricity and heat) and chemical. Chemical properties are the changes in composition undergone by a substance when it is sub­jected to various conditions. The various changes can be physical and chemical. The physical properties tend to be temporary. In a chemical change the composition of the substance is changed and new products arc formed; these changes are permanent.

All pure substances can be divided according to their composition into two main classes: elements (metals and non-metals) and compounds.

Laboratory investigations of compounds follow two general tech­niques — analysis and synthesis. Analysis is breaking down (decompo­sing) the compound into its constituent elements. They in turn are then identified by qualitative analysis, and their relative weight or vol­ume is determined by quantitative analysis. The direct opposite of analysis is synthesis. Synthesis means building a compound from sim­pler substances or elements. For example, water is analyzed when an electric current is passed through it, decomposing it into hydrogen and oxygen; it is synthesized when hydrogen gas is burned in the presence of oxygen, forming water.

Nowadays the word assay can be applied to analysis in general, but in particular it means the analysis of pharmaceutical and official drugs. Assaying by dry methods is dry-assay and by wet methods — wet-assay. An assay balance is also called an analytical balance.

There are such kinds of the qualitative analysis (detection of the kind of substances present): chemical by means of precipitation or wet method, thermal by means of flame tests and blowpipe analysis, opti­cal by means of spectroscopic and crystal structure, electrical by means of electrolysis and high frequency spectra, mechanical by means of microscope analysis and specific gravity, and biochemical by means of microorganisms - yeasts. JJlie quantitative analysis (determination of the amount of substances present) can be mechanical by means of gravimetric methods (weighing the amount), volumetric methods (ti­trating the amount); thermal by means of combustion and combustion gases absorption; electrical by means of conductometry, mass spectra; and optical by means of colorimetry and fluoroscopy.