THE GREAT ALPINE TUNNELS. 



625 



application of the injector system. One of the first introductions of 

 this method was in the ease of the Pracchia Tunnel, on the main line 

 between Florence and Bologna, through the Apennines. This is a 

 railway of single line, and was built many years ago by the late Mr. 

 Brassev. There are 52 tunnels in all, but those on the eastern side 

 are of comparatively little importance. On the western slope the 

 gradient nearly throughout is 25 per 1,000 (or 1 in 40). a d it is here 

 the greatest difficulty exists. There are several tunnels whose lengths 

 approximate to 1,000, 2,000, and 3,000 yards, and the traffic is both 

 heavy and frequent, the locomotives very powerful, with eight wheels 

 coupled. 



Under any conditions of wind the state of the longest tunnel is bad, 



"^ CROSS SECTION 



PLAN 

 Fig. 6.— The Saccardo system of ventilating tunnels. 



but when the wind is blowing in at the lower end at the same time 

 that a heavy goods or passenger train is ascending the gradient a state 

 of affairs is produced which is almost insupportable, and one might as 

 conveniently travel in a furnace flue. 



A heavy train of dining and sleeping carriages, with two engines, 

 conveying one of the crowned heads of Europe and suite, arrived at the 

 exit of Pracchia tunnel with both enginemen and both firemen insen- 

 sible; and in other cases passengers have been seriously affected. 



Owing to the height of the mountain, no shafts are available; but 



Signor Saccardo places a ventilating fan near the mouth of the tunnel 



and blows air into it through the annular space which exists between 



the arch of the tunnel and the gauge of maximum construction. (See 



sm 1901 10 



