( 38 ) 
40, exhaust the conduits (through %, and &,, before the con- 
necting of s, and sg) and to fill the reservoir 29 with mercury 
through & and 45); 
5°. To connect the apparatus with the standard open manometer 
(through #j). 
When the apparatus is used as a manometer the bottoms of the 
waterjackets on to which the glass waterjackets are fastened with 
india-rubber, are screwed on to the flanges O at A (seefig. 3). The 
temperature is kept constant by means of circulating water!) and 
of the stirring rods 7, 79, 73, 74, While thermometers (not repre- 
sented in the figure) enable to read the temperature at differents 
heights. The stirring rods are suspended from the stand S|, which 
is constructed so that it can easily be removed. 
§ 5. Some remarks on cleaning, cementing and filling. The 
cleaning of the tubes is of great importance. Only when this is 
done with the greatest care, it is possible that the menisci remain 
perfect. As for the precautions to ensure this, I refer to Comm. 
No, 27. Attention must be drawn however to the fact that, without 
particular precautions it would be impossible to clean the tubes by 
boiling for instance with nitric acid. In the first place different 
parts of the walls are very thick; moreover they are very long and 
terminate on one end in a comparatively narrow tube, on the other 
end in an extremely narrow capillary tube, which almost closes 
them. The difficulty arising from this, was removed by placing the 
tubes, as shown in Pl. II fig. 2, in expressely made boiling-tubes 
of ordinary size in which the cleansing-liquid is poured also 
filling the manometer-tube (being not entirely shut on both sides), 
and is heated until the liquid begins to boil within the manometer- 
tube. 
Round the manometer-tube a platinum wire is slung, which prevents 
contact between manometer-tube and boiling-tube, and serves to take 
the manometer-tube out of the boiling-tube. 
In cementing the manometer-tubes in the flanges, we must take 
care that the axes of the two coincide. Therefore it seemed desirable 
to make special moulds in which the tube and the flange are fastened. 
(Compare fig. 3 Pl. II). 
*) I shall not dwell on this circulation. When the piezometers are used at tempera- 
tures much differing from that of the room we must surround them with liquid- 
or vapour-jackets (or liquid-jackets enclosed in vapour-jackets). 
