The Romance of Modern Chemistry

FLAME: WHAT IS IT? means of estimating the amount of fire-damp. It is only a rough estimate, however, which can be made in this way. In recent years a much more accurate method of estimating the amount of fire-damp in mines or of petroleum in air has come into vogue. The apparatus used is really a safety lamp in which hydrogen is burned instead of oil. In an atmosphere containing fire-damp “ caps11 appear on the hydrogen flame just as in the ordi- nary safety lamp, but owing to the fact that the hydrogen flame is much less luminous than the oil flame, the “ caps ” are more easily seen and measured. The accompanying Fig. 8 shows the nature of these “ flame caps,” and the way in which their length varies with the amount of fire- damp in the atmosphere. The gradual development of the Davy lamp is an interesting example of the way in which scientific work has been directed to the detection of danger and the preservation of life. It would indeed be difficult to estimate the saving of human lives which has resulted from Davy’s discovery of the valuable properties of metal wire gauze in relation to a marsh gas flame. 165