ylene and oxygen be mixed to produce the
greatest explosion?

7. Solve Problem 18, Chapter XVII, without using molecular weights.
Compare your results.

8. Solve Problem 10, Chapter XVIII, without using molecular weights.
Compare your results.

9. The specific heat of aluminium is 0.214; of lead is 0.031. From these
specific heats calculate the atomic weights of each of the elements.

CHAPTER XX

THE PHOSPHORUS FAMILY

==================================================
| | ATOMIC | | MELTING
| SYMBOL | WEIGHT | DENSITY | POINT
-----------+--------+---------+---------+---------
Phosphorus | P | 31.0 | 1.8 | 43.3 deg.
Arsenic | As | 75.0 | 5.73 | ---
Antimony | Sb | 120.2 | 6.7 | 432 deg.
Bismuth | Bi | 208.5 | 9.8 | 270 deg.
==================================================

~The family.~ The elements constituting this family belong in the same
group with nitrogen and therefore resemble it in a general way. They
exhibit a regular gradation of physical properties, as is shown in the
above table. The same general gradation is also found in their chemical
properties, phosphorus being an acid-forming element, while bismuth is
essentially a metal. The other two elements are intermediate in
properties.

~Compounds.~ In general the elements of the family form compounds having
similar composition, as is shown in the following table:

PH_{3} PCl_{3} PCl_{5} P_{2}O_{3} P_{2}O_{5}
AsH_{3} AsCl_{3} AsCl_{5} As_{2}O_{3} As_{2}O_{5}
SbH_{3} SbCl_{3} SbCl_{5} Sb_{2}O_{3} Sb_{2}O_{5}
.... BiCl_{3} BiCl_{5} Bi_{2}O_{3} Bi_{2}O_{5}

In the case of phosphorus, arsenic, and antimony the oxides are acid
anhydrides. Salts of at least four acids of each of these three elements
are known, the free acid in some instances being unstable. The relation
of these acids to the corresponding anhydrides may be illustrated as
follows, phosphorus being taken as an example:

P_{2}O_{3} + 3H_{2}O = 2H_{3}PO_{3} (phosphorous acid).

P_{2}O_{5} + 3H_{2}O = 2H_{3}PO_{4} (phosphoric acid).

P_{2}O_{5} + 2H_{2}O = H_{4}P_{2}O_{7} (pyrophosphoric acid).

P_{2}O_{5} + H_{2}O = 2HPO_{3} (metaphosphoric acid).

PHOSPHORUS

~History.~ The element phosphorus was discovered by the alchemist Brand,
of Hamburg, in 1669, while searching for the philosopher's stone. Owing
to its peculia