RESULTS OF TEST-From the records of a large number of experimental investigations, the following results are selected:
I. Apparatus without piston-
1. Machines acting by simple displacement of water: useful effect, 6 to 40 per cent.-Experiments of MM. Romilly and Worms (Annales des Mines).
2. Entrainment apparatus: useful effect, 41.50 per cent.-Same experimenters.
II. Hydraulic piston apparatus - Sommeiller compressor improved: useful effect, 84 per cent.-Daxhelet's experiments (.Revue Universelle de,& Mines).
III. Apparatus with piston acting directly on air-London
Pneumatic Telegraph compressor: useful effect, 87 per cent.-Tested
bv constructor (Engineering, 1874). Schacht compressors, Saarbruck
mines: air compressed to 4 atmospheres, 80 per cent. In power
utilizable at driven shaft of compressor, with expansion of one-half,
about 40 per cent. ; at 3 atmospheres, 84 1/2 per cent. ; at 1
atmosphere, 91 per cent.-Hasslacher's experiments (Annale8
des Mines Prussiennes, vol. xvii.). Ryhope Collierv compressor:
average useful effect, 66 per cent.-Taylor's experiments ( Transactions
of North of England Institute of Minning and Mechanical Engineers,
vol. xxi.). As a rule, it may be stated that the useful effect
of the most improved compressors is 80 per cent. at average rate
of travel.