The chest breathers were from classes "civilized" and more or less "cultured." Nature has provided that for quiet breathing when at rest the air shall pass through the nose.

But when a person is taking active exercise, and consequently demands more air, he naturally and of necessity opens the mouth so as to breathe more fully.

While speaking or singing the air is necessarily taken in through the mouth.
BREATH CONTROL Firmness of tone depends upon steadiness of breath pressure.
Steadiness of tone depends upon a control of the breath which allows a minimum volume of air to pass out under sufficient tension to produce vocalization.
The tension and flow of breath can be gradually lessened until the tone vanishes and not even a whisper remains.
Power and largeness of tone depend first upon the =right use of the resonant cavities=, and second upon the =volume of breath used under proper control=.
In producing high tones the breath is delivered in less amount than for the low tones, but under greater tension.

Absolute control of the breath is necessary to produce the best results of which a voice is capable.

Full control of the breath insures success to a good voice; without it the best voice is doomed to failure.
When muscular action is fully mastered, and the proper method of breathing understood and established, the muscles of inspiration and expiration will act one against the other, so that the act of breathing may be suspended at any moment, whether the lungs are full, or partly full, or empty.