256 Mr. Cavendish’s Account of fome 
lowiffi, and afterwards of a greenifh or bluiffi hue. This 
colour did not go off by {landing, but continued at leaft ten 
days, during which time the acid conftantly kept that colour, 
except when by hafly freezing it {hot into fmall filaments, in 
which cafe it put on the white appearance which thefe acids 
always affumed under thofe circumftances ; but once that by 
gradual freezing it fhot into tranfparent ice, this ice was of a 
bluiffi colour. 
It is difficult to conceive what this colour ffiould proceed 
from. Spirit of nitre is well known to affume this colour 
when much phlogifticated and properly diluted ; but one does 
not fee why it ffiould become phlogifticated by the addition of 
the fnow, and ftill lefs why the dephlogifticated acid fhould 
become more phlogifticated thereby than the common acid did ; 
for though it is not extraordinary, that a procefs not capable 
of producing any increafe of phlogiftication in the common 
acid, fhould make this as much phlogifticated as that, yet it is 
very extraordinary that it ffiould make it more fo. No notice 
is taken of any effervefcence or difcharge of air while it was 
affuming this colour, nor was it obierved that it became more 
fmoking thereby, or that the top of the phial in which it was 
kept became full of red fumes, as might naturally be expedited 
if it was rendered much phlogifticated. Thefe are circum- 
ftances which, confidering Mr. M c Nab’s great attention to fet 
down all the phenomena that occurred, I ffiould think would 
hardly have been omitted if they had really happened. 
15, It is remarkable, that in both thefe experiments the 
addition of fnow produced heat, until it arrived pretty exadtly 
at what was found to be the freezing point of the diluted acid ; 
but that as foon as it arrived at that point, the addition of 
tnore fnow began to produce cold. This can hardly be owing 
merely 
