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ELECTRICAL MEASURING INSTRUMENTS For the detection or measurement of electric current, potential difference, and resistance certain instruments have been devised viz. The galvanometer for the detection of small currents measurements of small currents of the order of micro amperes or mili amperes the voltmeter or potentiometer for the measurement of potential difference (and voltage) between two points of a circuit are the EMF of a source the ammeter for the measurement of large currents the wheatstone bridge the meter Bridge the post office box and the ohmmeter for the measurement of resistance. THE MOVING COIL GALVANOMETER The moving coil galvanometer is a basic electrical instrument it is used for the detection (and Measurement) of small currents. Its underlying principle is the fact that when a current flows in a rectangular coil placed in a magnetic field it experiences a magnetic torque. If it is free to rotate under a controlling torque, it rotates through an angle proportional t...
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INDUSTRIAL PREPARATION OF HYDROGEN 

In industry, Hydrogen is manufactured from water,natural gas and ammonia..Methods are arranged in the order of their importance :

(i)Electrolysis of Water :

When electricity is passed through water containing a small amount of an electrolyte (an acid ,a base or salt) water decompose into hydrogen and oxygen.Hydrogen collects at cathode and oxygen gas, a by-product,is collected at anode.

2H2O ----------> 2H2 + O2

The gases produced are in the purest form.This process is expensive and is used to produce hydrogen where electricity is available at cheaper rates.

(ii)Steam and Hydrocarbon Process :

A mixture of steam and natural gas when over nickel catalyst at 900 C produces a mixture of hydrogen and carbon monoxide commonly known as Water gas, Natural gas contains about 94.60 % methane

CH4 +H2O ---------- > 3H2 + CO

(iii)By the action of steam on coal :

When steam is passed over red hot coke at about 1000 C, a mixture of hydrogen and carbon monoxide ( water gas ) is formed.

C + H2O --------- > H2 + CO

Hydrogen is obtained in free state by removing carbon monoxide from water gas . It is done by heating the mixture of two gases with more steam at 500 C  the presence of catalyst (Iron oxide or cobalt oxide). As a result carbon monoxide is changes to carbon dioxide which can easily be separated by dissolving in water under high pressure leaving behind free hydrogen gas.

CO + H2 +H20 -------- > CO + 2H2

CO can also be removed by cooling water gas at-200 C,with the help of liquid air.Carbon monoxide becomes liquid and free hydrogen gas is separated.Traces of carbon monoxide are further removed by passing the contaminated hydrogen through sodium hydroxide solution which absorbs carbon monoxide to form sodium formate.

CO + NaOH ------------ > HCOONa

(iv)Steam Methanol Process :

A mixture of steam and Vapour of methanol when heated at 250 C produces a mixture of hydrogen and carbon dioxide

CH3OH + H2O ----------> CO2 + 3H2

Carbon dioxide is separated by passing the mixture through water under high pressure where by CO2 will dissolve in water and free hydrogen gas is obtained.

(v)Thermal Decomposition of Hydrocarbon :

Methane (a major constituent of natural gas) when heated in the absence of oxygen,is decomposed into its elements.

CH4 ------------> C + 2H2

Carbon thus obtained is known as "Carbon Black" which is a by - product and is used in rubber industry specially as fillers for tyres.It is also used as a pigment of ink,plastics,paints,type writer carbon papers etc.

(vi)Thermal Decomposition of Ammonia:

This process consist of vaporizing the liquid ammonia from cylinders,heating it at 1000 C and passing it over an active catalyst.

2NH3 ------------> N2 + 3H2

The mixture of nitrogen and hydrogen is cooled to - 196 C when nitrogen becomes liquid and free hydrogen gas is obtained.





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