195 
6'tcam Engine. 
O 
forriis, in which a separate condenser has been introduced^ 
I sometimes employ oil (or any other sabsiaoce lighter 
than water, and capable of being kept Hiiid in the tempe- 
rature employed, without being converted into vapour,) 
in the upper part of the tube or pipe attached to die steam 
vessel : by which means steam of any temperature may 
be used without being exposed to the risk of partial con- 
densation by the admission of any colder body into the 
steam vessel ; for the oil, or other substance employed for 
this purpose, soon acquires the requisite temperature ; 
and to prevent unnecessary escape of heat, I construct of, 
or line with, an imperfect conductor of heat, that part of 
the tube or pipe attached to the steam vessel which maj^ 
not be heated exteriorly. And further, (as is already 
the practice in some engines, and therefore not exclu« 
sively claimed by me,) I cause the water raised by the 
engine to pass off through another ascending tube than the 
one attached to the steam vessel, but connected with it 
at some part lower than the oil or other substance 
ployed in it is ever suffered to descend to in the working 
of the engine. The improvement which I have just men- 
tioned, of introducing oil into the pipe attached to the 
steam vessel of such engines, may also be introduced 
without applying heat externally to the steam vessel? 
but in this case part of the effect which tvould otherwise 
be gained is lostd^ 
Description of a Portable Steam Engine. By Mr. Ma- 
thew Murray. 
To Mr. NICHOLSON. 
Sir, 
1 take the liberty of haiidiiig you the description of a- 
portable steam engine of my construction, which you will 
have the goodness to insert in your Philosophical Journah 
j will just observe it is reduced to the fewest parts that 
