Experiments on freezing Mixtures . 849 
fpirit of nitre diffolved ,535 of its weight of marble, and the 
undecanted part ,523 ; for which reafon I fhall call the ftrength 
of the former ,535, and that of the latter ,523 ; which mode of 
reckoning is obferved in the remainder of this Paper. The 
ftrength of the decanted part of the dephlogifticated acid was 
,56, and that of the undecanted part ,528 ; fo that it appears 
that in each of thefe acids the unfrozen part was a little 
ftronger than the frozen part. It is remarkable, that in the 
common fpirit of nitre, the decanted part, though ftronger 
than the other, was paler coloured and lefs fuming. 
8. On Dec. 21, the temperature of the air being -28% 
fome dephlogifticated fpirit of nitre (N° 27.) of nearly the 
fame ftrength as the former acid, was poured into a jar, in 
order to be diluted with fiiow, as recommended in Art. 2. Im- 
mediately after it was decanted, it began to freeze, in the fame 
manner as before defcribed, except that a lefs portion of it 
feems to have congealed : its temperature, tried by dipping a 
thermometer into it, was — 19 0 , where it remained ftationary 
for many minutes; it was then diluted with fnow, as will be 
mentioned in Art. 14. whereby its ftrength was reduced to 
5 434 * 
9. On Dec. 29th, this diluted acid was completely melted, 
and half of it poured into a jar with a ground ftopper, and 
both portions expofed to the air. In the morning they were 
perfectly fluid ; but on taking the ftopper out of the jar, 
and dipping in it a thermometer, the acid immediately froze, 
beginning by forming a white coat round the ball of the ther- 
mometer, which gradually fpread through the whole fluid ; 
and at the fame time the thermometer rofe till it flood ftatio- 
nary at - 5 0 . The cold of the acid before it began to freeze 
mu ft have been about -30°!, that being the temperature of a 
Vol. LXXVI, K k glafs 
