308 Mr. Coleman and Prof. McKendrick [May 29, 



in the form of mechanical power, but not necessarily, as for instance 

 in the ammonia absorption machine) before the ivhole volume of 

 the gaseous medium can be reduced in temperature, and not only 

 is this necessary, but in order to enable the medium, when it has 

 arrived at atmospheric temperature, to be employed for a fresh cycle of 

 operations, energy must be introduced and then rejected. 



In the case of atmospheric air the energy used in compression 

 appears as heat every cycle which has to be rejected, and this is 

 accomplished either by washing the air with injected water or by 

 passing it through tubes surrounded by water. 



Some idea of the heat required to be removed each cycle is afforded 

 by the fact that compression of air to the extent of 65-86 lb. per 

 square inch above the atmosphere increases its temperature by 332^ F. 



It is now about five years since machinery of this kind came into 

 extensive use, and for a long time there was a curious controversy 

 amongst engineers as to the two methods of removing the heat pro- 

 duced by compression. It was maintained that the water injection 

 would wet the air, but the lecturer showed by expanding a cubic foot 

 of air at 100 lb. pressure per square inch standing over water in the 

 theatre of the Institution, that on emerging from the iron bottle 

 containing it, it was exceedingly dry, which indeed followed from the 

 fact discovered by Dalton that saturated vapour is liquefied by com- 

 pression at a constant temperature, in direct proportion to the degree 

 of compression. In practice, however, especially at sea, the air pressure 

 is kept about 50 lb., and the dryness of the air is further ensured 

 by passing it, on its way to the expansion cylinder, through an inter- 

 changer, around the outside of which the partially cold air flowing 

 to the compressor is made to circulate. 



A number of large diagrams and a complete model were shown, 

 showing the general construction of the cold-air machines used 

 for imj)orting meat into Great Britain, all of which were now manu- 

 factured after the general designs introduced by the lecturer a few 

 years ago and described to the Institution of Civil Engineers in his 

 paper read there in February 1882. 



By means of these machines Australian, Eiver Plate and New 

 Zealand mutton comes into Great Britain at the rate of 18,000 sheep 

 or 400 tons per week, which represents a weekly procession a mile 

 long and ten abreast. The quantity of American meat carried by the 

 machines is still larger, so that the British householder is now 

 supplied by them with meat to the value of between 4,000,000/. and 

 5,000,000Z. j9er annum, calculated at the price of meat in retail shops.* 



These machines, in an ordinary way, supply streams of atmo- 

 spheric air cooled to about 80° below zero F. ( - 63° C.) ; but, by 

 certain modifications, tliey can be adjusted to deliver the air cooled 



* According to the Smithfield Market reports, 27,007 tons of mechanically 

 cooled meat arrived from U. S. America in 1884, and 5500 tons Australian, 

 New Zealand, and River Plate frozen mutton in first three months of 1885. 



