490 



NATURE 



[April 20, 1876 



The work was begun from two points, Airolo and 

 Goeschenen, the two extremities of the future tunnel. 

 The advance of the gallery, which is pushed on with 

 activit)', produces about 400 cubic metres of rubbish a 

 day at each of the two faces of attack. To carry away 

 this mass of rubbish, which is thrown regularly into 

 trucks running on rails, it is impossible to employ loco- 

 motives, as the C2d de sac nature of the galleries prevents 



Fig. 



effectual ventilation. The high price of horses and the 

 large number required prevent their use. The idea sug- 

 gested itself of making use for St. Gothard of machines 

 moved by compressed air, which would have many advan- 

 tages. First, it is well known that compressed air is 

 used to work the perforating machines used in boring the 

 tunnel ; then by the employment of compressed air loco- 

 motives ventilation of the galleries would be produced, as 



these machines would allow only pure air to escape ; and 

 then these motors would be more powerful than horses, 

 and effect more rapidly the clearing away of the debris. 



A first attempt was made in which two ordinary loco- 

 motives were employed, one at each side of the tunnel ; 

 the boilers, in which, of course, there was no water, were 

 filled with condensed air under a pressure of four atmo- 

 spheres. This air played the part usually done by steam, 

 passed into slide valves, entered the cylinders 

 alternately on each face of the pistons, which 

 it set in motion, and then escaped into the 

 atmosphere. 



It is easily seen that if compressed air were 

 to be employed, it would be indispensable to 

 have a very considerable quantity of it ; the 

 boiler of a locomotive, sufficient when it is 

 worked by means of steam constantly pro- 

 duced under the action of heat, was too small 

 to contain a quantity of air sufficient for use 

 without being filled. This led to adding to 

 each locomotive a special reservoir for com- 

 pressed air ; each locomotive was accom- 

 panied, as a kind of tender, by a long sheet-iron 

 cylinder, 8 metres long and \\ metres diameter, supported 

 towards its extremities by two trucks, which, on starting, 

 were filled with condensed air, and which communicated 

 by a tube with the distributing apparatus of the cylinders. 

 The locomotive then worked as before, except that com- 

 pressed air came from the reservoirs instead of from the 

 boiler. The two locomotives, the Reiiss and the Tessm, 

 worked economically for about two years, in spi^e of the 



Fig. 2. — Compressed Air Locomotive used at the St. Gothard Tunnel Works. 



awkwardness of the long cylinders that accompanied 

 them. We can give some interesting figures resulting 

 from the mean of a certain number of observations. At 

 departure the pressure in the reservoir was about 7 kilo- 

 grammes per square centimetre ; the locomotive having 

 drawn a train of twelve loaded waggons along a course of 

 about 600 metres, the pressure was found to fall to 4^ 

 kilogrammes ; the train then returned empty to the point 

 of deoarture, and the final pressure was found to be 2^ 

 kilogrammes. 



In spite of the relatively advantageous results which 

 were obtained, the employment of compressed air in a 

 steam locomotive presented a certain number of draw- 

 backs. It is expedient that the air should issue from 

 the cylinder under the least possible pressure, in order 

 that refrigeration may be reduced to a minimum ; for 

 it is known that the expansion of gas is accompanied 

 by a loss of heat which increases with the pressure. This 

 condition was satisfied by causing the air to act under 

 restraint ; that is, by allowing the compressed air coming 



