638 PROCEEDINGS OF THE AMERICAN ACADEMY. 



able to use any commercial drawn tubing, but have found it necessary 

 to drill the tubing from the solid rod. The same grade of steel as that 

 used for the cylinders should be used for the drilled tubing. The 

 inside diameter of the tuljing is ^q of an inch, and it is quite possible 

 with a little practise to drill pieces at least 17 inches long. The drill 

 should be cut on the end of a long piece of drill rod; it does not pay 

 to try to braze a long shank onto a short drill. Two essentials in 

 successfully drilling a long piece of tube are to start with the drill 

 accurately central, and to use as homogeneous stock as possible. The 

 drill need not be expected to run more than ^ of an inch out of center 

 on a piece 17 inches long. After getting the drill accurately started 

 for two or three inches it will be found convenient to put the drill in a 

 hand tool holder and force it in by hand. This arrangement makes 

 it much simpler to run the drill in and out of the hole to remove chips. 

 Great care must be observed that the drill does not become clogged 

 with chips. I have found that it pays to carefully clean out the hole 

 with a swab after drilling not more than | of an inch. It is easy, if all 

 precautions are observed, to drill a hole yc of ^^^ i"*^^ ^'^ diameter 17 

 inches long in from seven to eight hours. 



After drilling, the rod is to be turned off over the hole to the final 

 size, so that the whole may be concentric, and then hardened in oil 

 and left undrawn, exactly as are the cylinders. 



The problem of the proper connections at the end of the pipe is one 

 that has given great trouble. The coned connection described above 

 was used for some time. The only change necessary from the form 

 used for lower pressures is the interposition of a hardened steel washer 

 between the soft cupped washer and the retaining screw. I have 

 successfully reached 12000 kgm. a number of times with this packing, 

 but ultimately rupture always occurred at the bottom of the threads. 

 It may be that rupture at this point is not a pure pressure effect, but 

 that the cylinders are too heavy for the tubing, so that there is some 

 slight bending at the thread under the unavoidable hard handling of 

 setting up the apparatus. Be that as it may, the cone packing is un- 

 satisfactory for long continued service, particularly at temperatures 

 much above that of the room. 



The packing for the connecting tube finally adopted, and which has 

 proved entirely satisfactory, is shown in Figure 10. The main im- 

 provement of this over the cone form is that it leaves the tube much 

 heavier, the minimum outside diameter at a point exposed only to 

 internal pressure being f of an inch in the new form against about j 

 of an inch at the bottom of the thread in the cone form. The end of 



