of dust; 2nd, the admixture of irrespirable gases produced by the explosion of gunpowder; and 3rd, its deterioration by respiration and combustion.
All the various labours of the miner tend to impregnate the air with minute earthy particles, and this impregnation is rendered much greater than it could otherwise be, by the great stagnation of the air in the extremities of the galleries, where these labours are chiefly performed. The kind and quantity of dust varies according to the nature of the rock and vein, the degree of humidity, and also according to the process by which the rock and ore are broken up. The constant presence of dust is sufficiently obvious to any one who visits the interior of a mine in a state of activity. I cannot say, however, that I was ever sensible of its presence from any immediate effects on the organs of respiration. Its prevalence is abundantly obvious in the smutty ochry complexions and dresses of the miner, or of the visitor of mines, in the dusty floors of such galleries as are perfectly dry, and in the layers of soft mud and turbid puddles that cover the bottom of all those which contain much humidity. A still more striking proof of the prevalence of this dust, and an instance more important to the subject of this essay, is the fact, confirmed to me by the testimony of many labouring miners, of the sputa being tinged by it for many hours after the miner leaves the mine, and of this tinge being varied in colour according to the nature of the rock and vein worked.
Except in those mines which are situated in soft slaty rocks, and whose lodes are also of a soft kind, (a very small proportion,) the use of gunpowder for
