CLARK: HARVARD DEEP-SEA THERMOGRAPH. 527 



Flask. 



Figure 14, Plate 5 shows the flask complete, a section of its lower 

 part, and some small pieces. The flash is cylindrical in general shape, 

 3-]^ inches in diameter, and about twenty-one inches in length over 

 all. For the greater portion of its length it has an inner diameter of 2^g 

 inches, the walls being | inch thick. Below this portion it tapers off 

 and is continued as a small cylindrical tube | inch in diameter outside 

 and five inches long with walls only g inch thick. The flask here shown 

 was made by the Hoffecker Company of Boston from a single forging 

 of chrome-vanadium steel. Very little is known about the design of 

 tubes to withstand great external pressure, and it is hard to say to 

 what depth this flask may be sent safely. It may be found that for 

 5,000-fathom work the walls must be thicker. 



The small pieces, Plate 5, fig. 14, constitute the plug which closes 

 the upper end of the flask proper. The stud H passes freely through 

 the piece /, but is prevented from rotating by the nearly square head 

 at J, which fits in socket K. Four screws prevent this head from fall- 

 ing out of the socket, but it may move up and down freely ^ inch. 

 This shake is an essential feature. Pieces H and I need not be taken 

 apart save for cleaning. To put the plug in place this unit is first 

 inserted in the flask proper and screwed down until it nearly bottoms. 

 The piece / may be required to withstand a force as great as 35 tons. 

 It is essential, therefore, that the stress come on the threads rather 

 than on the shoulder of the flask. Next there are put on three packing 

 rings in order — fibre, soft rubber, and fibre. Above these is placed 

 the nut L, which is set up tight with a wrench. As the water-pressure 

 on this plug increases, the rubber is compressed slightly and the 

 tension of the stud on the nut decreases and finally disappears. Since 

 the stud may slide freely through the nut L, the force due to water 

 pressure on the whole plug will be transmitted to the packing. The 

 cross-section of the whole plug is about 3 greater than that of the 

 packing ring, and consequently the rubber will be subjected to a 

 pressure 3 greater than the water-pressure outside, which will prevent 

 leakage at the edges. However, the excess is not great enough to 

 spread the flask nor to drive the rubber out through the joints. 



A collar of wrought iron shrunk on the flask and held in place by a 

 shoulder is provided with a pair of trunnions to carry the bail by which 

 the flask is supported. 



The inner diameter of the flask is je inch greater than the tliameter 

 of the works, and the inner diameter of the tube at the bottom of the 



