169 
the tube as far as the pump would draw, without bringing 
the mercury down, so that I had a column of 35 inches of 
mercury suspended by the cohesion of the liquids. 
There was no reason to suppose that this was the limit 
or anywhere near the limit. It was clearly possible to sus- 
pend a longer column, but as the length of the column 
increased so would the difficulty of getting rid of the dis- 
turbing causes, and I determined to rest satisfied with the 
35 inches ; but in order to see if this could be maintained, 
I obtained a gauge 60 inches long, so that this would leave 
30 inches above the pressure of the atmosphere. 
The difficulty of getting rid of the air in this tube suffi- 
ciently to allow of the mercury standing 60 inches was very 
considerable. Before filling the tube it was rinsed out with 
concentrated sulphuric acid, then 
twice washed with distilled water, 
and then water put in and boiled in 
the tube. Then sufficient mercury 
was introduced to fill the long leg 
and the bend, so that the column 
when complete was 59 inches long, 
the barometer being at 29 5 . 
After the tube had been tilted 
several times so as to allow the air 
to pass out, the mercury would be 
suspended as the tube was slowly 
re-erected, until it had attained an 
elevation of 40, 50, or sometimes the 
full height, as shown in Fig. 3 ; but 
only for a few seconds. When the 
mercury fell, if the column broke 
anywhere near the top of the tube, 
it gave way with a loud click. But 
this was by no means always the case. 
The mercury would sometimes sepa- 
Fig. 3. 
