杏吧原创

Bee lines 1

Question: Children at my school are always asking me how bees make honey. Can
anyone help me explain?

Answer: Honeybees collect both nectar and pollen from flowers, but only the
nectar is used to make honey. The pollen is transported back to the hive in
baskets on the bees鈥� hind legs, while the nectar is carried in the honey
stomach. When full, the honey stomach can make up more than a third of a forager
bee鈥檚 unladen weight, making its abdomen visibly longer.

Nectar is essentially a solution of sugar in water, usually between 25 and 50
per cent sugar. Back in the hive, the nectar is placed in honeycomb cells and
the excess water evaporates over a few days until the honey is approximately 83
per cent sugar. Each cell is then covered with a layer of wax. When large
amounts of nectar are drying, the bees help the process by using their wings to
blow air through the hive.

Preventing the nectar from spoiling is crucial, because it may not be eaten
for months. The evaporation of the excess water breaks down the sucrose in the
nectar into two smaller sugars, glucose and fructose. This creates a solution of
sugars too concentrated for yeast and other micro-organisms to grow in.

As well as sugar, nectar contains small amounts of other chemicals that give
different honeys their distinctive colours and flavours. The bees from any one
colony will collect nectar from hundreds of different plant species during the
summer, but at certain times they gather large amounts of nectar from just one
or a few locally abundant species. The nectar from these collections accounts
for most of the honey the bees produce, and beekeepers often harvest honey after
such a nectar flow, thereby obtaining honey with a flavour and colour
characteristic of a particular plant.

Francis Ratnieks

Laboratory of Apiculture & Social Insects

Sheffield University

Answer: Bees make honey by drying out the nectar they collect from flowers.
The older bees forage for nectar, which they return and deposit in open wax
honeycomb cells in the hive. There can be in excess of 60,000 bees in a healthy
hive and it鈥檚 not unusual for them to collect 20 kilograms of nectar per
day.

Younger bees have the task of forcing air through the hive to speed the
evaporation of water from the nectar. If you watch a beehive you will see one
group of bees gripping the hive at one side of the entrance and blowing air into
the hive by fanning their wings. Another group of bees on the other side of the
entrance will be facing the other way, drawing air out of the hive.
Strategically placed fanning bees inside the hive direct the airflow.

Drying the nectar to make honey means it will keep for a very long time.
Unspoilt honey has been found in the burial chambers of the pharaohs in the
pyramids of Egypt.

Richard Hyde

Mountain View, California

Water weight

Question: I have seen a catalogue from a fire extinguisher manufacturer that
advertised extinguishers filled with 鈥渓ight water鈥�. What on Earth is light water
and, more importantly, why would you put it in a fire extinguisher?

Answer: Light Water is a trademark owned by 3M for a firefighting foam
designed to tackle fires fuelled by 鈥渃lass A鈥� materials鈥攐nes which leave a
residue of ash when they burn. Class A fires were traditionally fought with
water, but now firefighters often use foam.

Although water has a high specific heat capacity, its strong surface tension
causes it to bead up and roll away from the fire before it can draw much heat
from the flames. But adding chemicals to form a foam reduces the surface
tension.

According to Class A Foam: Best practice for structural
fire-fighters by Dominic Colleti, (Lyon鈥檚 Publishing, 1998), foam is up to
five times as effective as water alone, so the fire can be extinguished more
quickly with less water damage to property.

Geoff Harmer

Reading, Berkshire

Answer: I鈥檓 a scientist with the local Safety and Environment Authority in
Zurich, and I also act as a chemical disaster expert for the firefighting
department.

Light Water is a registered trademark of 3M and is a combination of chemicals
that includes glycol derivatives, detergents and surfactants, a mixture also
known as aqueous film-forming foam, or AFFF. As a dilute solution in water, it
forms a light, stable foam used primarily to fight fires involving flammable
organic liquids.

The foam floats on the surface of the burning liquid鈥攈ence 鈥淟ight
Water鈥濃�攃overing it with a thin surfactant film that prevents further
evaporation of the liquid and extinguishes the fire by cutting off the oxygen
supply.

Used correctly, these additives can substantially reduce the amount of water
that is needed to extinguish a fire.

Jesper Hansen

Zurich

Spearhead assault

Question: What is the physics involved in achieving the maximum range when
throwing a javelin? How is it affected by the angle at which it is thrown, and
what forces act on the javelin during the flight? (continued)

Answer: The last answer included an error. The vertical distance is reduced
by the pull of gravity, not increased. Instead of +1/2gt² it should be
鈭�1/2驳迟².

George Felton

Woking, Surrey

This week鈥檚 questions

Pipe dream: During a conversation about playing the bagpipes at high
altitude, I wondered what would happen to the sound of the bagpipes if they were
played in the helium/oxygen mix used by deep-sea divers, which distorts speech.
Would the double-reed chanter (the output part of the bagpipe that consists of a
tube with holes and is played with the fingers) be affected in the same way as
the single-reed drones (the output pipes confined to single notes)?

Roger Malton,

Errol, Tayside

We鈥檇 love to know if anyone has tried this and whether the bagpipes
sounded any better鈥擡d

Vanishing birds: What happened to the sparrows in London? There used to be
millions. Now I see maybe two a year. Did cats eat them all?

Robert Share

London