Why should a special boiling tube used for carrying out boiling tube determination be thoroughly washed and dried before another determination is carried out?
Answers
Answer:
T HE laboratory apparatus for carrying out reactions, in general, is made up
of glass. It is because glass is resistant to the action of most of the
chemicals. Generally, two types of glass are used for making apparatus
for laboratory work. These are soda-lime glass and borosilicate glass.
Soda-lime glass, which is made by heating soda, limestone and silica, softens
readily at about 300-400°C in the burner flame. Therefore, on heating glass
tubings made of soda-lime glass easily softens and can be bent. Coefficient of
expansion of soda glass is very high, therefore on sudden heating and cooling, it
may break. To avoid breaking, it should be heated and cooled gradually. Annealing
by mild reheating and uniform cooling prevents breakage. Such glass should
not be kept on cold surface while it is hot, since sudden cooling may break it.
Borosilicate glass does not soften below 700-800°C and requires oxygen-
natural gas flame for working. Natural gas mixed with oxygen is burnt to get the
oxygen-natural gas flame. Coefficient of expansion of this glass is low and
apparatus made of this glass can withstand sudden changes in temperature.
Therefore, apparatus used for heating purposes is made from borosilicate glass.
On heating, glass apparatus made up of borosilicate glass does not distort.
In the following pages you will learn about some of the techniques of handling
glass tubes and glass rods without injuring yourself. Also, you will learn the
techniques of using laboratory apparatus and equipments.
2.1 CUTTING OF GLASS TUBE AND GLASS ROD
Material Required
• Soda-glass tube : 15 cm long
• Soda-glass rod : 15 cm long
• Triangular file : One
Procedure
(i) Place the glass tube or the glass rod on the table and press it with your left