I I 6 Mr. CAVENDISH 's Al count oj 
Diminution 
'Diminution on (baking ni 
in trying 
trpus 
air Jor 
com mon air. 
one minute 
• wo minutes. 
1.099 
. 1 18 
.122 
UiitiUed water. 
1 04 9 
,c8 3 
.08 s 
Water from tub. 
1 0,^6 
.090 
.098 
Pump water. 
1.062 
j Diililled water, in which a few drops of liver 
• ^ y O 
.099 
i of iulphur were kept for a few days. { 
r Diftilled u r ater impregnated with nitrous air^ 
1-045 
.052 
.056 
j by keeping it with about -4- of its bulk of ni- 
] t rous air for tv\ 0 days, and frequently fhaking 
h it. 
.897 
.082 
^0 
00 
q 
j Water fouled by oak (havings. N. B.. it 
[ frothed very much. 
In general, the diminution was nearly as great with rain 
water as diftilled water ; but hornet imes I have found rain 
water froth a good deal, and then the diminution was not 
much greater than by the water fouled with oak (havings. 
This difference in the diminution, according to the nature of 
the water, is a very great inconvenience, and feems to be the 
chief caufe of uncertainty in trying the purity of air; but it is 
by no means peculiar to this method, as I have found as great 
a difference in fontana’s method, according as I have filled 
the tube with different waters*. But it fhews plainly, how 
little all the experiments which have hitherto been made for 
determining the variations in the purity of the atmofphere can 
be relied on, as I do not know that any one before has been 
attentive to the nature of the water he has ufed, and the dif- 
ference proceeding from the difference of waters is much greater 
than any I have yet found in the purity of air. 
* I do not find that it makes much difference in fontana’s method whether 
the water is difpofed to froth or not ; but the advantage which it has in that 
refptft ever this method is not of much ccnfequence, as it is eafy finding water 
which will not fxoth. 
The 
