UTILISATION' OF GASES. 65 



power can be obtained from the same quantity of fuel as when 

 using high-class steam engines. 



Mond gas is now being supplied over a considerable area in 

 South Staffordshire, England. The gas is delivered at a pressure 

 of 5 lb. per square inch, the diameter of the trunk mains is 36 

 inches, and the longest distance to w^hich it is carried 8 miles. It 

 is supplied at a price of IM to 2M per 1000 cubic feet, and there 

 are over one hundred consumers. The capacity of the plant at 

 this central station is about one milUon tons of coal per annum. 



The Mond gas producer is chiefly of use for large installations ; 

 for the far more numerous but smaller plants suction gas producers 

 are employed, burning a better class of fuel. 



I cannot leave the subject of producer gas without touching 

 upon its use for fuel purposes. It contains more of the original 

 energy of the fuel than any other gas, and is now largely used for 

 heating purposes. The chief advantages over direct coal firing 

 are that a higher temperature and more exact regulation of air 

 are attainable, the furnace temperature is under absolute control, 

 no smoke is produced, labour costs are reduced, a saving in weight 

 of fuel is readily obtained by efificient gas firing, and it is generally 

 possible to use a cheaper fiiel. 



The next subject I propose to deal with is refrigeration, where 

 we meet with another important and interesting use for gases, and 

 more especially for the three gases — ammonia, sulphur-dioxide, and 

 carbonic acid. 



The first form of machine used commercially was one invented 

 by Dr. Gorrie, of New Orleans, in 1845, in which compressed air 

 was employed, although Perkins had taken out a patent for an 

 ammonia machine as early as 1834. Air machines, owing to the 

 difficulty of rapid exchange of heat, are very inefficient, and the 

 vapour compression machines, viz., those employing as working 

 substance a gas which by compression can be reduced to liquid 

 form have now almost entirely displaced all other forms of 

 . refrigerating machines. 



The first vapour compression machine to be used commercially 

 was one employing sulphuric ether as working substance, and was 

 introduced by James Harrison, of Geelong. The author of the 

 book in which this statement occurs remarks : — " It is certainly 

 interesting to find a colonial engineer taking this important step 

 in the development of the process, and it is appropriate, for 

 certainly no parts of the world have profited more from mechanical 

 refrigeration than have the AustraUan colonies." 



On its introduction by Harrison, the ether machine quickly 

 came into general use, but is now obsolete on account of serious 

 drawbacks in comparison with other vapour compression machines. 

 These use either ammonia, carbonic acid, or sulphuric dioxide. As 

 regards efficiency — i.e., cold produced for energy supplied — 



