568 



NATURE 



[April 13. 1893 



introduction was found useful in the preliminary arrangements 

 and in testing for leaks. The connection between the lower 

 chamber B and the vessel in which the pressure is to be verified 

 takes place through a side tube, E. 



The greater part of the column of mercury to which the 

 pressure is due is contained in the connecting tube FF, of about 

 3 mm. internal diameter. The temperature is taken by a ther- 

 mometer whose bulb is situated near the middle of FF. 

 Towards the close of operations the more sensitive parts are 

 protected by a packing of tow or cotton-wool, held in position 

 between two wooden boards. The anterior board is provided 



with a suitable glass window, through which the thermometer 

 may be read. 



It is an essential requirement of a manometer on the present 

 plan that the measuring rod pass air-tight from the upper and 

 lower chambers into the atmosphere. To effect this the glass 

 tubing is drawn out until its internal diameter is not much 

 greater than that of the rod. The joints are then made by short 

 lengths of thick walled india-rubber H, G, wired on and 

 drowned externally in mercury. The vessels for holding the 

 mercury are shown at I,K. 



The distance between the points of the rod is determined 



under microscopes by comparison with a standard scale, before 

 the apparatus is put together. As the rod is held only by the 

 rubber connexions, there is no fear of its length being altered by 

 stress. 



The adjustment of the mercury (distilled in a vacuum) to the 

 right level is effected by means of the tube of black rubber LM, 

 terminating in the reservoir N. When the supply of mercury 

 to the manometer is a little short of what is needed, the con- 

 nexion with the reservoir is cut off" by a pinch-cock at O, and 

 the fine adjustment is continued by squeezing the tube at P be- 

 tween a pah: of hinged boards, gradually approximated by a 

 screw. This plan, though apparently rough, worked perfectly, 

 leaving nothing to be desired. 



It remains to explain the object of the vessel shown at Q. In 

 the early trials, when the rubber tube was connected directly to 

 R, the gradual fouling of the mercury surface, which it seems 

 impossible to avoid, threatened to interfere with the setting at 

 B. By means of Q, the mercury can be discharged from the 

 measuring chambers, and a fresh surface constituted at B as well 

 as at C. 



Connexions tvith Pump and Manometer. 

 Some of the details of the process of filling the globe with 

 gas under standard conditions will be best described later under 

 the head of the particular gas ; but the general arrangement and 



rF\ 



NO. 1224, VOL. 47] 



the connexions with the pump and the manometer are common 

 to all. They are sketched in Fig. 2, in which S represents the 

 globe, T the inverted bell-glass employed to contain the enve- 

 loping ice. The connexion with the rest of the apparatus is by 

 a short tube U of thick lubber, carefully wired on. The tight- 

 ness of these joints was always tested with the aid of the 

 Tcippler X, the tap V leading to the gas generating apparatus 

 being closed. The side tube at D leads to the vacuum chamber 

 of the manometer, while that at E leads to the pressure chamber 

 B. The wash out of the tubes, and in some cases of the gener- 

 ator, w as aided by the Toppler. When this operation was judged 

 to be complete, V was again closed, and a good vacuum made 

 in the parts still connected to the pump. W would then be closed, 

 and the actual filling commenced by opening V, and finally the 

 tap of the globe. The lower chamber of the manometer was now 

 in connexion with the globe, and through a regulating tap (not 

 shown) with the gas-generating apparatus. By means of the 

 Toppler, the vacuum in the manometer could be carried to any 

 desired point. But with respect to this a remark must be made. 

 It is a feature of the method employed ' that the exhaustions of 



1 Due to von Jolly. 



