Man's physical universe



sodium hypochlorite, which sells as a 5 per cent solution in water under

many names, such as " Clorox," " Purex," " Zonite," etc. This solution

is one of the most powerful of all the disinfectants and one of the least

harmful to the delicate tissues. It is widely used under various fanciful

names for use in disinfecting utensils in the dairy industry. Because

of its bleaching action it is also valuable in laundry work.

The use of hypochlorites as disinfectants dates from World War I,

when Dakin's solution, prepared by the action of chlorine on sodium

carbonate with the addition of a little

Science to the call

boric acid, was the answer of

of military surgeons for a disinfectant to stop the

tremendous loss of life due to infections.

Incidentally, the use of chlorine as a war gas or as a constituent of

other war gases saved many more thousands of lives because it disabled

many soldiers so that they had to be taken to hospitals where they

were in less danger of being blown to pieces by the shells of the enemy.

Bromine and iodine, two other active nonmetals belonging to the

same periodic family called the halogen family, are present in sea

water. Bromine is obtained directly from sea water or from certain

salt wells, but it is not used extensively as a disinfectant, although

hypobromites are excellent disinfectants and bromine may be substituted

for chlorine for use in disinfecting water.

Iodine is still one of the

best disinfectants, and the ordinary solution of iodine in alcohol,

called tincture of iodine, is familiar to nearly everyone.

Iodine may be

obtained from seaweeds, the Chilean nitrate deposits, or petroleum

brines as mentioned above.

The lightest and most active halogen is the greenish-yellow gas,

fluorine. A few of its compounds hydrolyze to produce hydrofluoric

acid, which is destructive to animal life. Such compounds are therefore

a frequent ingredient of insect and ant powders, and they are also

poisonous to human beings.

The chief use of fluorine and hydrofluoric

acid is in etching glass, inasmuch as fluorine reacts with glass to form

a soluble compound, silicon tetrafluoride.


1. Discuss soap as to (a) what it is, (6) how it is made, (c) kinds of soap, and

{d) what it is used for.

2. Discuss hardness of water as to (a) kind of hardness, {h) how it is removed, and

(c) why it is objectionable.

3. Discuss the purification of water as to (a) the types of impurities that are

objectionable for different purposes, and {h) how these impurities are removed.

4. Discuss abrasives as to (o) what an abrasive is, {b) naturally occurring

abrasives and their uses, and (c) artificial abrasives and their uses.

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