Basic Laboratory Techniques
In This Post Let’s Talk About Some Of The Basic Laboratory Techniques, Which We Use In Our Labs. So, Let’s Start These Topics: Basic Laboratory Techniques, Basic Laboratory Techniques PDF, Basic Laboratory Techniques PPT, Basic Laboratory Techniques Book, Basic Laboratory Techniques Hindi.
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Regarding a chemical laboratory, Michael Faraday’s words come true
“We come here to be philosophers, and I hope you will always remember that whenever a
result happens, especially if it is new, you would say, what is the cause? Why does it occur? And you will in course of time find out the reason.”
The chemistry laboratory is a center of learning where the students develop their power of
observation by performing the experiments of various types using the apparatus of different kinds. The heating device in the chemistry laboratory is the Bunsen burner. It has a simple construction with the following parts.
(a) The base (b) The gas tube (c) The nipple (d) The metallic tube or barrel (e) Air regulator.
Points to remember for the Bunsen burner
1. Before lighting the burner always make sure that the air regulator works freely and all connections are airtight.
2. Never blow to put out the flame of the burner. Always turn it off from the gas tap.
3. Never throw solid material into the flame. This will spoil the working of the burner.
4. For heating purposes always use the tip of the burner flame and not the middle portion.
Sometimes the flame of a burner is found to strike back inside the barrel, it indicates that the air hole is too big to give a non-smoky flame or the pressure of the gas coming in the burner is low. The flame strikes back in order to get more fuel. In this case, the air hole is adjusted properly to get a non-smoky flame. Since the barrel has become hot, it is not advisable to touch it.
Handling and manipulation of glass tubing
Cutting a glass tube or rod.
Place the glass tube or rod flat on the benchtop. Hold it firmly with the help of your left hand and make one sharp scratch with the help of a sharp triangular file at the point where the tube to be cut as desired. Push the file away from you to make this scratch. It should not be moved back and forth, only one firm stroke is required for the purpose.
Now hold the rod or tube firmly placing one hand on each side of the scratch mark with the
two thumbs, touching each other as shown in figure – 2.
Your thumb should be on the opposite side of the scratch. Now pull the tube or rod back gently by pressing thumbs forward (against the glass). It will give a clear and sharp break. In case if the break is not clear, keep the sharp freshly cut edge rotating in the flame for a while so that it is rounded off as shown in figure – 3.
Bending a glass tube
It needs a horizontal flame. Use a flame spreader to obtain a horizontal flame from the Bunsen burner. Hold the glass tube to be bent with the help of both the hands, one on each end as shown in figure – 4. (Be sure that the ends are fire-polished and cool).
Hold the tube lengthwise in the horizontal flame at the point where the bend is required. Now rotate the tube evenly and carefully to make the glass soft and the heated portion begins to sag. Bring away the tube from the flame and bend it gently to the required shape-holding it in this position until the glass becomes hard. The bend should be in one place. Good and poor bend is shown in figure – 5.
Note: It should be noted that the bend should never be at 90° as shown in figure 5 (III). In this case, the inner ends of the arms are nearly blocked and will not allow the fluid to pass. Figure– 5 (I) shows a proper bend.
Drawing out a glass Jet
Light a Bunsen burner. Hold the required glass tube, with both the hands, one on each end. Hold the tube lengthwise and rotate it gently and evenly until the glass becomes soft and heated portion begins to sag. Now remove the tube away from the flame and allow it to cool slightly. Now rotate it while pulling the ends apart till the capillary of required size is obtained as shown in figure – 6.
The middle portion can be cut and removed using a sharp triangular file as shown in figure – 7 and you get two droppers in hand.
The jets so obtained are used for different purposes such as making wash bottles,
medicine droppers, melting point tubes, washing precipitates, etc.
Boring a cork
Many times in the laboratory we need to pass a glass tube through a cork stopper such as the preparation of gases, making wash bottles for different purposes. For this, it is required to the borehole, one, two, or more through cork stoppers.
(i) Selection of cork of the correct size
The cork should be of the size which fits well in the neck of the vessel in use and should
be strong enough to bear the pressure when the hole of proper size is bored in it.
(ii) Pressing of Cork
Press the cork with the help of a cork presser as shown in figure – 9. Press the cork. between the wheel of the presser and the grooved plate. Now press the handle lever at times.
(iii) Selection of Cork Borer
Cork borers are available in various sizes. Since the glass tube is to be fixed tightly in the
cork a borer is selected which is slightly smaller in diameter than the glass tube.
What are cork borers?
They are metallic tubes having a sharp edge at one end and handle at the other. When a borer is used for a long time it loses in sharpness and becomes dull. A special sharpener is used to sharpen it to make it useful.
(iv) Actual boring
Wet the cork borer with little glycerol in order to give it smoothness. Now hold the borer in the right hand and the cork in the left pointing the narrow end upwards. Place the sharp end of the borer at the center of the cork as shown in figure – 10.
Align the borer parallel to the axis of the cork. Twist and press till the borer is halfway through the cork. Check the alignment after each twist. Now place the cork on a wooden borer and twist the borer vigorously until it cuts through the cork. Remove the stem of the cork from the borer with the help of a cleaning rod.
(v) How to insert glass tubing in stoppers?
Make the tube and stopper wet with soap solution or glycerol or simply with water. Before
using the tube be sure that the ends of the tube are fire polished. Now grasp the tube near the point of insertion and rotate the tube back and forth while pushing it gently into the stopper.
Please Note: (i) Do not apply too much force to push the tubing through the stopper.
(ii) Wrap your hands in a towel for protection.
(vi) How to remove glass tubing from stopper?
Apply soap solution or glycerol to lubricate the tubing which is to be pulled through the stopper. Wrap the tubing with a towel. Pull the tubing from the stopper with a gentle twisting motion. If the tube gets stuck to the stopper, insert the end of the stout wire between the tubing and the stopper and rotate it gently. If this procedure fails, take the smallest size cork borer available which fits over the tubing through the stopper and work it out.
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