340 Mr. Carl Barus on the 



Screw- Compressor. 



2. The apparatus (Plate IX. fig. 1) consists essentially 

 of a strong wrought-iron barrel, ABC, the head of which, 

 A A, is suitably threaded, so that a steel screw, S S T, can be 

 forced into it. The piezometer tube is attached at the end, 

 C C, of the barrel. Barrel and tubes are quite filled with oil. 



3. To obviate leakage I make use of two special devices, 

 the first of which is the tinned screw. This is an ordinary 

 well-cut machine screw of iron or steel, covered with a uni- 

 form thin adhesive layer of ordinary solder, by dipping it 

 (after cleansing with soldering- salts) in a vessel of the fused 

 metal. When forced into their sockets, these screws secure 

 complete freedom from leakage, even at 2000 atmospheres 

 and more. Gauges and other appurtenances may thus be 

 attached to the barrel, and removed from it, with facility. 



The other device is the gasket of marine glue*, or other 

 highly viscous liquid. A stuffing-box is easily made, by 

 which this substance is kept pressed against the threads of 

 the screw, or against the smooth surface of a cylindrical 

 plunger. The cement admits of being shaped by pressure 

 to fill up any cavity, but it is far too viscous to flow through 

 capillary interstices. In a preceding paper f 1 found its 

 viscosity to be 20 billion times the viscosity of water. 

 Pressure, moreover, tends to close up all fissures between 

 nut and screw, thus making the apparatus more efficient at 

 high pressures than at low pressures, even if the cement 

 should not itself increase in viscosity. 



4. To rotate the screw S S T (figs. 1 and 3) it is provided 

 with a lever (three feet long) and ratchet, LDE. The steel 

 ratchet-wheel, R R, forged to the shaft T of the screw, is 

 square-cut to correspond with the right-and-left click D. A 

 pin, E, sliding in a socket of the lever, L, and actuated by a 

 spring (fig. 1), enables the operator to adjust the ratchet 

 either for forward or retrograde motion of the screw S T. 



The screw S 8 is one inch in diameter with twelve threads 

 to the inch. 



5. The barrel, B B, is secured between guides, on the 

 planed front of the bed-plates, F F, by two bolts (figs. 1 and 4) . 

 The rear of the bed-plate is hollowed to catch drippings. 



The gland, K K, of the stuffing-box is of steel, and is pro- 

 vided with a large flange for screwing it forcibly in place. 



* Supplied, among- others, by Ducretet of Paris, and by the Soci6te 

 Genevoise. Perhaps pitch, or even molasses candy, would be similarly 

 serviceable. 



t Barus, Phil. Mag. xxix. p. 337 (1890). 



