tell you about the atmosphere itself. I have written on this diagram the composition of one hundred parts of atmospheric air:—
| Bulk. | Weight. | |
| Oxygen, | 20 | 22.3 |
| Nitrogen, | 80 | 77.7 |
| 100 | 100.0 |
It is a true analysis of the atmosphere, so far as regards the quantity of oxygen and the quantity of nitrogen present. By our analysis, we find that 5 pints of the atmosphere contain only 1 pint of oxygen, and 4 pints, or 4 parts, of nitrogen by bulk. That is our analysis of the atmosphere. It requires all that quantity of nitrogen to reduce the oxygen down, so as to be able to supply the candle properly with fuel, so as to supply us with an atmosphere which our lungs can healthily and safely breathe; for it is just as important to make the oxygen right for us to breathe, as it is to make the atmosphere right for the burning of the fire and the candle.
But now for this atmosphere. First of all, let me tell you the weight of these gases. A
