Jan. 20, 1887] 



NA TURE 



277 



Mr. Sturgeon has adopted very special cooling arrange- 

 ments for his compressors. Firstly, the air used is all 

 taken through the roof of the engine-house, and thus 

 heating by contact with the boilers and engines below is 

 avoided. It is filtered of deleterious dirt in entering 

 through the roof. Secondly, the compressor cylinders are 

 surrounded by ample water jackets, through which a con- 

 tinual fresh-water circulation is kept up. Thirdly, the 

 delivery-valve — it is a single large disk of slightly greater 

 diameter than the cylinder — is made hollow, and through 

 it a cold-water circulation is kept up, the water being 

 spread out in a thin radial stream across the valve face 

 over which the air flows as it leaves the cylinder. This 

 cooling-water is supplied to the hollow valve through a 

 tube sliding in a stuffing-box in the cylinder cover. A 

 further development of this system would be a supply of 

 cooling water to the face of the piston after the manner 



that the steam is supplied to the piston-jacket of the low- 

 pressure engine cylinder ; but this refinement has not 

 been deemed necessary in the design as at present 

 adopted. 



The compressor piston-face travels a little beyond the 

 position assumed by the flat face of this delivery-valve 

 when the latter is closed. During the momentary pause 

 at the end of the stroke, the valve therefore falls into 

 actual contact with the piston-face, and the two descend 

 together until the valve is landed on its seat. Thus the 

 clearance space is reduced absolutely to zero. 



The suction-valves are somewhat similarly arranged so 

 as to reduce the clearance at the other end of the stroke 

 to a very small amount. The cooling-water is circulated 

 by gravity from a tank giving a head of 20 feet. The 

 water is pumped into this tank from the canal, and the 

 power spent in pumping this water is a partial set-off 



against the economy resulting from the approximation to 

 isothermal compression ; but the power thus gained 

 greatly outweighs the work spent in this pumping. 



As at present designed, the air-pipes are of wrought- 

 iron plate, riveted, but a new design for plate-steel tubes 

 is being considered. The pipes are to be laid in concrete 

 tunnels, which free them from all pressure of superincum- 

 bent soil or paving, and will always be very accessible for 

 examinationandrepair. Theyareof 24 inchesdiameternear 

 the central station, and diminish to 7 inches in the smallest 

 branches. The joints are given a small degree of flexi- 

 bility. In one design they are formed by two angle- 

 irons riveted to the outside ends of the two pipes, a hard 

 rubber ring of circular section being placed between the 

 flanges thus formed, and the flanges being drawn together 

 by bolts. In another design a sort of double-socket 

 coupling-piece covers the ends of both pipes for a few 

 inches ; the end of each pipe has formed on it two slightly 



projecting rings, and between these is poured, in the 

 molten state, through a hole in the socket-coupling, a soft 

 metal that expands during solidification. We rather doubt 

 whether this last design will give sufficient tensive strength 

 to the joint. Tensive strength is required simply 

 because there are necessarily bends in the pipe here and 

 there. 



The air is supplied to the consumer through a register- 

 ing meter. This meter is similar in construction to 

 Beale's gas exhauster. It consists of two cylinders, one 

 inside the other. Both are 4 inches long ; the outer one 

 has a diameter of 14 and the inner a diameter of gf 

 inches. The outer one is fixed, and is furnished with an 

 inlet and an outlet opening. The inner cylinder revolves 

 freely on a fixed axis, distant ^(14-9^) = 25^^^ inches away 

 from the centre of the outer case, so that the two cylinders 

 always touch along a fixed line. Two sliding shutters 

 project from a slot through the centre of the revolving 



