ARTIFICIAL REFRIGERATION AND ICE MAKING, LXIX. 
metal, the fracture being very crystalline. Triple expansion 
engines driving compressor direct have been made previously to 
that mentioned by Mr, Statham. Single acting compressors are 
often preferred, both on account of the stuffing box being subject 
to the suction pressure only, and also to the easier adjustment of 
the clearances. 
The machine which the author considered embodied most of the 
points of the ideal machine as formulated in the paper, certainly 
did offer a very direct course for the gases, and being compound 
gave a much more equable resistance throughout the revolution of 
the crank than non-compound compressors possibly could. He 
had seen one of the authors machines at work and it certainly 
ran very steadily, it was not bolted down in any way but simply 
resting on blocks of wood. 
Mr. Sroxes said that in his historical remarks the author had 
omitted to mention the Sulphuric Acid Atmospheric Machine, 
which although successful was not an unqualified success, because 
the sulphuric acid absorbed so much water it had to be renewed 
frequently, and was consequently intermittent. He (Mr. Stokes) 
thought that an ideal machine should consist of few parts all of 
ample size ; he would consider the single acting compressor with 
duplex cylinders preferable, the vertical type of compressors with 
horizontal engine required the most attention and more floor space 
would be necessary, but the increased efficiency would compensate 
forthat. In certain types of machines, which like the “Hercules” 
have two valves on the top cover, the valves do not require to be 
very large to take up the compressed gas. He objected to com- 
pound machines—if, when something happened to one side of it 
the whole machine was laid up; with the duplex machine if one 
Part breaks and an overhaul is necessary, the other portion can 
be kept working while repairs are effected. 
Professor WARREN said, we may illustrate the changes which 
& substance undergoes in a direct heat engine or a reversed engine 
by means of pressure—volume or entropy—temperature diagrams, 
Mr . Selfe had made use of the well known pressure volume dia- 
