850 Report of the Committee 
5thly, Though, as was faid before, this appears to be 
the moft accurate way of adjufting the boiling point ; yet, 
if the operator was to fuffer the air to have any accefs to 
the inlkle of the velfel, he would be liable to a very great 
error: forthisreafonwe ftrongly recommend it to all thofe 
who ufe this method, not to deviate at all from the rules 
laid down without alluring themfelves, by repeated trials 
with a pretty fenlible thermometer, that luch alteration 
may be ufed with fafety. But the covering the chimney 
with the tin plate ought by no means to be omitted ; for 
though, if the cover of the pot fits clofe, it feldom figni- 
fies whether the plate is laid on or not, yet, if by acci- 
dent the cover was not to fit clofe, the omitting the tin 
plate would make a very great error. Making the chim- 
ney very narrow would not anfwer the end properly; 
for, if it was made fo fmall as to make the veffel fuffici- 
ently clofe when the water boiled gently, it would not 
leave fufficient paffage for the efcape of the fleam when 
the water boiled fall. 
Another way of adjufting the boiling point is, to try 
it in a veffel of the fame kind as the former, only with 
the water riling a little way, namely from one to three 
or four inches above the ball, taking care that the boil- 
ing point fhall rife very little above the cover, as in the 
former method. In this method there is no need to cover 
the 
