A Simple Gas Generator
A simple gas generator can easily be set up as described below. It works on the same principle as the Kipps apparatus. It can be adapted to produce several different gases. Two designs are shown below: use whatever apparatus you have available.
(a) Using an inverted tap-funnel (b) Using a gas-drying tube
(Mount the whole assembly, well clamped, on a stand.)
Put a charge of solid chemical in the The tube should be fitted with a
When the tap or pinch valve are opened the acid can move up the apparatus, reacting with the solid and generating gas. The gas will be evolved in a steady stream until the acid or solid is used up. Try and ensure enough acid to cover the solid and thus get maximum gas generation.
This generator can be used for other gases where the reaction involves the reaction of an insoluble solid with water or an aqueous solution, and heating is not required e.g. ethyne (acetylene) from calcium carbide and water.
The photo below shows a bomb calorimeter in use at Irish Cement Ltd. (Limerick Works), where it is used to measure the fuel value of the coal used for firing the cement kilns. The oxygen supply can be seen at the right and the actual bomb is dismounted on top of the main calorimeter body.
Mercury thermometers are expensive and are dangerous because they are easily broken, releasing mercury into the laboratory. Do we have to use mercury-in-glass? Looking through a catalogue of science equipment reveals that one can buy alcohol-in-glass thermometers (up to 110ºC x1ºC) for less money than the equivalent mercury-in-glass thermometers. Alcohol thermometers are much safer, as well as being cheaper, and this temperature range covers most laboratory needs. Mercury thermometers would be needed above 110ºC e.g. 0-360º thermometers for m.pt. determination.
Other alternatives are the use of electronic thermometers (using thermocouples or thermistors as sensing elements). These are too expensive at present for widespread use, but the digital models are ideal for demonstrations. The expanded scale demonstration meters with temperature probes and scales are also useful.
Stop the rolling thermometer!
Most breakages of thermometers are due to them rolling off benches or when they are being inserted (or removed) from stoppers (see p.8). Some brands of thermometers now come with anti-roll caps that fit on the end of the thermometer and simply stop them rolling. You can do this yourself by putting a small cork or rubber stopper on the end of the thermometer, with one flat face cut on the stopper. This will stop the thermometer rolling.
Thermometers should, anyway, be placed down perpendicular to the edge of the bench (not parallel) and returned to a safe storage place after use. A tray with spaces, similar to that used for pipettes (see issue 2, p.24), made from expanded polystyrene makes a safe store. It also gives a see-at-a-glance check if any are missing, presumed broken.
A cheap, convenient test-tube holder can be made using wooden spring clothes-pegs. 3 dozen of the smaller type cost about 50p. The plastic variety are NOT suitable. The small clothes-pegs can be used directly to hold small test-tubes. They give a firm grip, unlike some metal tongs, and are poor conductors. Fingers may be too close to the flame, and screwing on a longer strip of thin wood to one side makes them safer. (You can buy a version similar to this – but its cheaper and more fun to make your own.) A larger version of the wooden spring peg is available in some shops and enables larger test-tubes to be held securely.
“The penetration of microwaves and their loss of energy is different for different substances and even for a given substance depends on its physical state. As I have said before, water is a good absorber of microwaves, and this is because under the influence of the microwave electric field the water molecules rotate or oscillate and then through friction their kinetic energy is converted into heat. In ice, on the other hand, the water molecules are rigidly anchored in the crystal lattice and are hardly affected by the microwaves, which therefore pass through ice almost unhindered. The following simple demonstration can illustrate this. A cup of water is placed in a hollowed-out block of ice, and after about 30 seconds in the microwave oven the water boils while the surrounding ice remains frozen.”
With issue 2 I sent out a safety poster. I said then, and I repeat, you can’t display that poster until you make safety spectacles or goggles available. If you, the teacher, don’t wear them routinely for preparing classes and doing demonstrations, then you’ll never get the message over to your pupils. In fact, you are more likely to have an accident than them!
I heard of a case recently of a technician making up sodium hydroxide solution from pellets, WITHOUT eye protection. The unforeseen accident happened – they are usually unforeseen. A pellet jumped out into his eye and began to eat it away. Solid sodium hydroxide is extremely caustic with a strong, exothermic affinity for water. He lost his eye. Even dilute alkali splashes in the eye have been known to produce fogging of the cornea. It does not pay to take chances.
Can I make a stronger case for you and your pupils to wear safety glasses/goggles at all times in the laboratory when practical work is being done? Eye protection is cheap – about £1·50 - £2·00 per pupil, and well worth it to prevent even one accident in ten years. You and/or the school are likely to be sued if an accident does happen and you haven’t taken ‘reasonable precautions’. Most laboratory suppliers will supply safety glasses or goggles, at a price. You are better to try a supplier of industrial safety equipment, even a local hardware shop stocks them, for a better price since you will need at least 30 pairs for an inter-cert class.
“The contributions of the chemist to culinary art and to many other activities designed to increase out sensual pleasures are well-known. The chemists analyse and explain fragrances and flavours and often invent new ones; a vast chemical industry is concerned with producing dyes to please our eyes. Physicists, on the other hand, either alone or in the company of engineers, are, in the public mind, usually associated with all the nasty and unpleasant things: supersonic bangs, hydrogen bombs, our transport problems caused by internal combustion engines…”
USE PIPETTE FILLERS ROUTINELY