238 Letier from Dr. Pricfiley....Letieg from Dr. Beddoes. [OE 
light; and why may not pholgificn efcape 
their refearches, when they employ the 
fame jnftruments in the ir.veltigation. 
3. When mercury is revived from red 
ecipitate in inflammable air, it has 
te faid that the pure air from this {ub- 
ftance, uniting with the inflammable air 
that difappears, forrns water. But be- 
fides that I find no fufficient quantity ~ 
of water when the experiment is made 
over mercury, itis evident, from my late 
experiments, that neither water, nor any 
thing elfe, is formed by it; fince it is 
found diffufed through the inflammable 
air that is left, and has. more than once 
eccafioned. an explofion of the veffel in 
which the experiment is made, to the no 
fmall danger of the operator. I have, 
however, fometimes ftopped the procefs, 
in order to examine the ftate of the air; 
and on comparing the quantity of the in- 
flammable air that had difappeared, and 
that of the pure air diffufed through it, 
Y find, by an eafy method of computa- 
tion, that an ounce of mercury mevived 
inthis manner, abforbs not lefs than 362 
eunce meafurcs of inflammable air, which 
is more than the fame quanity of Jead or 
bifmuth require. Of the former I have 
revived an ounce with ro8 ounce mea- 
fures of the inflammable air, and of the 
latter with 185. ~ 
Now fince the fame precipitate may be 
revived ina glafs veflel with a red heat 
without any addition, and the mereury 
fe revived cannot be diftinguifhed from. 
that which has imbibed the great quan- 
tity of inflammable air above-mentioned, 
the philofopher has only the choice of 
thofe two difficulties ; viz. that the pre- 
cipitate attratts phlogiften through the 
hot glafs, or that the addition of fo much 
inflammable air, or fomething contained 
in it, and effential to it, makes no fenfible 
change in its properties- 
In thefe experiments J found no fixed 
air in the water over which the procefs 
was made, though at other times I have 
found fome: but this is not very extra- 
ordinary, fince I have fufficiently proved 
that fixed air does confit of an union of 
pure air, and inflammable air, though I 
have not afcertained the circumitances om 
which this union is always formed. 
By inferting thefe articles in your 
very valuable publication, you willoblige, 
Sir, yours, 
Northumberland, 
Aug. 22, 1798 
J. PRIESTLEY. 
P.S. Inthe fourth coluran of the ar- 
ticle in March you have printed exfure 
inftead of conjume.. 
To the Editor of the Monthly Magazine. 
Sir, 
Doubt not but a variety of perfonsy 
eager to fix their opinions concerning” 
the medicinal power of gaffes, have ac- 
cufed me of tardinefs in the eftablifhment: 
of the Pneumatic Inftitution. No accu- 
fation however could be worfe founded, 
J have never ceafed to exert myfelf te 
bring the defign to bear; but it is ob- 
vious that I had two ferious difficulties 
to overcome. Had I begun ‘without 2 
certain fund, or without a fuyerintendant 
qualified to ¢onduét the enquiry, I fhoulé” 
have failed altogether, and done a lafting 
injury to a good caule.; fuppofing (what 
i firmly believe) that mankind can be. 
benefited by endeavours of this nature. 
The fum fubferibed is adequate to 
many trials. 
will not fall far fhort of that /ubferibed. 
It is poflible that fome perfons forbear 
to contribute till they fee the inftitution om 
foot: The addition of rocoel. or z000l. 
at moft, would probably enable us to com- 
plete the prefent object, that is, to bring 
out decifive refults, venether favourable 
or otherwife. Should any of your read- 
ers be difpofed to yield us pecuniary af- 
fiftance, they would find an account eper 
at the houfe of Thomas Coutts, Ejg. 
banker, Strand; or they may forward 
their contributions to me. 
The difficulty refpecting a fuperintend- 
ant was-much the greater of the two ; 
but in my judgment it is moft complete- 
ly overcome. A young man, endowed 
with talents for experimental refearches 
at leaft equal to any perfon I have ever 
known, has at my earneft folicitation 
confented to undertake this moft difficult 
charge. 
interefted themfelves in promoting the 
defign, approve my choice; and with 
the reft I am willing to pledge my whole 
eredit upon it. After a very fhort time, 
no one will need to rely on my judgment. 
Mr. Davy has completed a courfe of 
experiments on the chemiftry of light 
and heat, which will appear in the fuit 
volume of the We/f-country Contributions, 
and will, I think, go far towards fettling 
many important. points belonging to this 
abftrufe fubje&t. All imaginable means 
to fecure authenticity and publicity fhall 
‘be employed ; I fhall deferibe in a fepa- 
rate paper fuch as occur to me, and thofe 
which others may fuggeft we thal] wil- 
lingly adopt. The city of Briftol and 
its populous neighbourhood, will, we 
hope, afford an ample fupply of patients. 
I am, Sir, yours, &c. 
Cyften, O6F. Ge Tuo, BEDDOES. 
The fubfcribers who have moft 
™~ 
I hope the fum collefed - 
