VtNTILATION OF MINES OR HOSPITALS. S33 



^hile the air is forced into a pipe branching from the air- 

 ▼esseK and which is to be continued to the part of the 

 mine >vhere the supply of fri^h air is required. 



I have found, however, that the forcing into vitiated air This an im- 

 a mixture of that which is purer, even when the bestP*"^^*^^' '^^"^*^^^' 

 means are used, though a measure which aflfords relief, is 

 not in bad cases a complete remedy; and where the opera- 

 tion depends on manual labour, or any means that are not 

 unremitted in their action, it becomes quite ineffectual. 

 The foul air, charged with the smoke of gunpowder used 

 in blasting, and which it strongly retains, is certainly me- 

 liorated by the mixture of pure air, but is not removed. 

 While the biasi continues, some of it is driven into the 

 other parts of the mine; but when the influx of pure air 

 ceases it returns again, or if during the influx of pure air a 

 fresh volume of smoke be produced by explosions which 

 are constantly taking place, it is not until some time after- 

 ward that it becomes sutliciently attenuated for the work*- 

 men to resume their stations with comfort. 



A consideration of these circumstances led me to think, Pumping out 

 that the usual operation of all ventilating engines ought to be ^^ V\^']^, ^^ 

 reversed, to afford all the advantages that could be desired; 

 that instead of using the machines, which serve as con- 

 densers, exhausters should be adopted ; and thus, instead of 

 forcing pure air into that in a vitiated state, a complete 

 remedy could only be had by pumping out all that was ira- , 



pure as fast as it became so. 



Many modes of doing this suggested themselves to me. Modes sug- 

 by the alteration of the machines commonly applied, and ^*^^^*^* 

 by producing an ascending stream of air through pipes by a 

 furnace constructed for the purpose. The latter mode 

 would however have beeq here expensive in fuel, as well as 

 in attendance; and the others required power to overcome 

 the friction of pistons, aiid so on, or considerable accuracy 

 in construction. 



I at last erected the machine, of which the annexed is a Machine for 

 •drawing, which, whiie it is so simple in construction, ^"^^j^^/S^** 

 requires so small an expense of power, is so complete in its 

 operation, and its parts are so little liable to be injured by 

 ir^xir^ ihat^ as far as I can imagine, nothiag mpre caa be 



desired, 



