292 D*\ Pk test ley’s Experiments and Obfervations 
1 found to anfwer very well during the procefs, though they 
never failed to break in cooling. At length I procured a tube 
of copper , on which, as M. Lavoisier difcovered, fleam had 
no efFed ; and at laft I made ufe of earthen tubes, with which 
Mr. Wedge wood, that mod: generous promoter of fcience, 
liberally fupplied me for the purpofe ; and thefe glazed on the 
outfide only 1 find far preferable to copper. They are, indeed, 
every thing that I could wifh for in experiments of this kind ; 
the reafon of which will appear in my account of another courfe 
of experiments, which I hope to lay before the Society in due 
time. 
The difpofition of the apparatus, with which thefe experi- 
ments were made, was as follows. The water was made to boil 
in a glafs retort, which communicated with the copper or 
earthen tube which contained the charcoal or iron, &c. and 
which, being placed in an horizontal pofition, was furrounded 
with hot coals. The end of this tube oppofile to the retort 
communicated with the pipe of a common worm tub , fuch as 
is generally ufed in diff illations, by means of which all the 
fuperfluous fleam was condenfed, and colleded in a proper re- 
ceptacle, while the air which had been produced, and had 
come along with it through the worm tub, was tranfmitted 
into a trough of water, where proper vefiels were placed to 
receive it, and afcertain the quantity of it ; after which I 
could examine the quality of it at leifure. 
In the experiment with charcoal , I found unexpe&ed diffi- 
culties, and conflderable variations in the refult ; the proportion 
between the charcoal and water expended, and alfo between e<tch 
ofthemand the air produced, not being fo nearly the fame 
as I imagined they would have been. Alfo the quantity of 
fixed air that was mixed with the inflammable air varied very 
much. 
4 
