852 Report of the Committee 
but if the operator fhoulil be apprehenfive that there 
is, it is eafily prevented by fattening an iron ring an 
inch or two broad round the pot near the bottom. This 
precaution is equally neceflary when the thermometer is 
adjufted in fteam, efpecially when there is not much 
water in the pot. 
The greateft inconvenience of this method of a dj lift- 
ing the boiling point is the trouble of keeping a proper 
depth of water in the pot, as to do this it is neceflary firft 
to find the height of the boiling point coarfely by try- 
ing it in an open veflel, and then to put fuch a quantity 
of water into the pot that it fhall rife from one to three 
or four inches above the ball, when the thermometer is 
placed at fuch a depth within the pot that the boiling- 
point fhall rife very little above the cover. The operator 
mutt be very careful that the quantity of water in the 
pot be not fo fmall as not intirely to cover the ball. 
A third way of adjufting the boiling point is, to wrap 
feveral folds of linen rags or flannel round the tube of 
the thermometer, and to try it in an open veflel, taking 
care to pour boiling water on the rags, in order to keep 
the quickfilver in the tube as nearly of the heat of boiling 
water as poflible. The beft w T ay is to pour boiling water 
on the rags three or four times, waiting a few feconds be- 
tween each time, and to wait fome feconds after the laft 
>n time 
