368 Historical 



At Strepy-Bracquegnies, all the laborers, except one, who worked 

 in air compressed to 3.70 atmospheres, and from 4 to 5 hours conse- 

 utively, were attacked, after leaving the apparatus, by more or less 

 acute pains .... These pains, the seat of which was chiefly in the 

 articulations, such as the knees, the shoulders, and the joints of the 

 arms, appeared in certain persons so severely that they sometimes 

 went more than forty-eight hours without being able to sleep .... 



It was noted that some laborers who had had rather severe attacks 

 and who had gone down to work were completely relieved of pain as 

 soon as they were in compressed air, but that the pains came on again 

 some time after they had left the apparatus. 



Besides these effects, the author again mentions unpleasant sting- 

 ing over the whole surface of the body and especially on the ex- 

 tremities. 



But compressed air is used chiefly on the foundation of bridge 

 piers, and it is under these conditions that hundreds of workmen 

 are exposed to its effects every year. It is therefore of interest 

 for us to explain briefly the mode of application of the Triger 

 method in this particular case. 



Figure 6 will permit us to be very brief in our explanations; it 

 is a cross-section which we borrow from the memoir of Dr. Foley, 

 which will be reviewed later. 



A cast-iron tube MM composed of concentric rings fastened 

 together by bolts m, and ending at the bottom of a widened cham- 

 ber or "crinoline," is let down upon the bed of the river in the 

 spot which the bridge pier is to occupy. It is topped at its upper 

 end by a room with 3 compartments; the one in the middle, F, is 

 in constant communication with the cast-iron tube; a blowing 

 machine, through a tube G, constantly pumps into it air which is 

 sufficiently compressed to drive all the water out of the cast-iron 

 cylinder, and escape constantly bubbling all around; the bottom 

 then becomes dry, as happens in a glass tube into which a child 

 blows after immersing it in water. 



Under these conditions, the workman who is coming to work 

 opens the door of one of the lateral chambers, E, and closes it 

 behind him, and by a cock communicating with the central cham- 

 ber F, equalizes the pressure of the air about him with that of the 

 air in the cylinder. When this has been done, he easily opens the 

 inner door, hitherto held shut by the pressure, and goes down to 

 the bottom of the shaft by a ladder. There he works and fills with 

 the earth which he digs out buckets which are hauled up and 

 emptied outside. Does he wish to leave? He goes to the other 

 lateral chamber C in which the air has remained under pressure, 

 goes in, closes the door, and by a cock communicating with the 



