ARTIFICIAL REFRIGERATION AND ICE MAKING. LIII. 
during both strokes (distributing the work over as large a portion 
of the crank pin’s path as possible); because with single and 
double acting cylinders of equal capacity and piston speed the 
single acting one must have double the piston area of the double 
acting one, and must therefore transmit double the stress to the 
connecting rod and cranks, 
If high mechanical efficiency and low working expenses are 
aimed at then :— 
6. In order to minimise the friction in the bearings and prevent 
the loss of power which results from indirect action, the connec- 
tion of the engine piston to the compressor piston should be as 
direct as possible, and the crank shaft, with the crank pins and 
connecting rods, should also if possible, take up and transfer the 
difference between the powers exerted and required by the steam 
and compressor pistons respectively at any given position, instead 
of the swm of these powers, during each revolution of the fly-wheel. 
Under a third head there are other points of importance con- | 
nected with the maintenance of the whole machine in working 
order as :— 
7. The pistons and valves should be easily accessible for exam- 
ination and renewal. The cylinders should be simple castings. 
8. All joints, and covers or bonnets should have plain faces, 
and such things as double or treble connections with bridges under 
One joint face should be avoided in order to make connections 
simple and certain. Lastly, all wearing surfaces should be adjust-— 
able and easily adjusted. 
THE WORK TO BE DONE IN A COMPRESSING CYLINDER. 
When a gas is compressed in a cylinder, the work performed by 
the piston is not uniform throughout its stroke for the reason 
that the pressure increases as the volume is reduced following a 
curve which is dependent upon the heat during compression. This 
curve is called “adiabatic ” when no heat passes from the cylinder 
during the compression of the gas ; and “ isothermal” if so much 
heat is transferred during the operation that the gas is maintained 
