Page 11 - Chemistry - XI

Basic Laboratory Techniques
1 Basic Laboratory Techniques

EXPERIMENT - 1

Objective
To cut a glass tube or a glass rod for diff erent uses.

Materials Required

Glass tube or glass rod, triangular fi le, asbestos sheet, and burner

Procedure
1. Marking a Scratch: Take a glass tube/rod free of cracks. Place it on the bench and hold fi rmly with
your thumb and draw a fi ne scratch with little pressure inwards using a triangular fi le.

2. Breaking the Tube/Rod: Now, hold the tube with both the hands ensuring that the thumbs are on
either side of the scratch and put pressure outwards.
3. Fire Polishing: If the ends of the tube/rod are not smooth, then to make the edges round and smooth,
fi rst trim the sharp edges by rubbing with a wire gauze. Heat the edge of the tube gently in the fl ame.
This method is known as fi re polishing.

In this method, the cut end is warmed over burner and rotated until the edge is rounded. If it is heated
too much, the rounded edge may distort.

File
Pull Scratch

Making a Scratch and Breaking

Fire Polishing the Tube

After continuously warming the cut end in a bunsen fl ame,
rotate back and forth until the edges are rounded.

Fig. 1.1
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