76 ANNUAL OF SCIENTIFIC DISCOVERY. 



mines by forcing clown air, some of our leading companies are 

 likely to roach a depth much below the point where tlie Sutro 

 tunnel will tap the lead before it is completed, even though work 

 upon it should be at once commenced. Should the Chollar- 

 Potosi Company continue downward witii their shafts at the same 

 rate of speecl that has distinguished their progress for some 

 months past, they would, in less than two years, attain a point 

 below that of the intersection of the Sutro tunnel witli the Corn- 

 stock lead. Whether another water stratum exists in the 800 

 to 1,000 feet of hot, unexplored region of rock lying between our 

 present lower levels and that point on the lead which would be 

 cut by the Sutro tunnel, no man can know." 



VENTILATION OP MINES. 



It having been asserted that the sole cause of the recent fright- 

 ful destruction of life at Avondale, in Pennsylvania, was the use 

 of a furnace for ventilating the mine instead of mechanical appa- 

 ratus, we give some extracts from a paper which was recently 

 read before the Institution of Mechanical Engineers, at New- 

 castle, England, by Mr. William Cochrane, and published in 

 The "Engineer:" — 



*' It is considered a fair estimate of the economic value of the 

 average conditions in which furnaces are worked that only one 

 fifth of the heat due to the combustion of the coal is utilized. 

 There are many objections, besides the small useful elTect, to the 

 use of a furnace, which cannot be overcome, and which form a 

 constant source of cost attendant upon it, namel}', the necessity 

 of cleaning the flues and the consequent suspension of the active 

 ventilation of the mine ; the inconvenience, and in some cases the 

 impossibility, of using a shaft highly heated, and often full of 

 smoke, for any other purpose than as a ventilating shaft; and 

 the serious damage done by the products of combustion to cast- 

 iron tubing, timber, pumps, or wire ropes, where winding is car- 

 ried on in the upcast shaft, especially where the shaft is damp. 

 If the conditions are unfavorable for the use of a furnace, suchas 

 shallow shafts and heavy resistances to be overcome, the furnace 

 then is quite unable to compete with a good mechanical ventilator 

 in economical eflect. In a table compiled by Mr. J. J. Atkinson, 

 Government Inspector for the Durham coal-field, has been shown 

 the depth at which the furnaces are estimated to be equal to ven- 

 tilating machines in point oi' economy of fuel, assuming that the 

 sources of loss are of the same extent in each case, that is, the 

 loss of fuel in furnaces by cooling in the upcast, and in ventilat- 

 ing machines utilized 00 per cent, of the engine-power. A recent 

 calculation by M. Guibal, of Mons, deduces the following com- 

 parison : That if a furnace in a 12-feet shaft, 400 j'ards deep, cir- 

 culate 5.'], 000 cubic feet of air per minute under the total resist- 

 ances represented by oj inch water-gauge, and an average 

 excess of upcast temperature of 108° above the downcast, witii a 

 duty of 31 lbs. of coal per horse-power in the air estimated on 



