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160. Steam-power. Steam Engines which are employed 

 in farming in highly civilised countries, are of three descrip- 

 tions, viz.. Stationary, Portable and Traction. Multitubular 

 boilers are now in general use. Ordinarily 2\ to 3lbs. of coal 

 are consumed per H. P. per hour. Low power stationary en- 

 gines are useful in farms for dairy purposes, e.g. for steaming 

 food, pulping and grinding and working the centrifugal cream 

 separator. Steam is mostiessential for keeping dairy utensils 

 clean and free from germs. Portable engines are in more 

 common use for ordinary farming. These are let out to 

 farmers who use them for thrashing and winnowing their 

 corn. The portable engines in general use are of 8 H P. 

 Traction engines which are more powerful still are used for 

 ploughing &c They are not yet popular even in England 

 and we need mnke no further mention of them here. 



161 . Gas Engines and Oil Engines are worked on the same 

 principle. In each case explosion results in the generation of 

 gases which under ordinary atmospheric pressure occupy more 

 space than the substance which exploded did before explosion. 

 By keeping these gases controlled within a cylinder and pre- 

 venting their expansion, pressure is generated on the walls of 

 the cylinder. A piston inserted inside this cylinder moves ex- 

 actly in the same way as the piston of a steam engine cylin- 

 der by force of the steam. Explosion of coal-gas is a well known 

 phenomenon. In the case of oil-engines an explosive oil, such 

 as Kerosine, is used. The oil is vapoured and ignited in the 

 presence of air which is introduced into the vapouring 

 chamber at the commencement of each stroke of the piston, 

 this resulting in explosion. As oil is far more conveniently 

 carried and stored, than coal, oil engines are getting very 

 popular for use in V farms ( which are usually situated in out- 

 lying districts where cartage comes expensive. The actual 

 expense is also less. In terms of coal, an oil-engine consu- 

 mes an equivalent of less than i\ Ibs. per H. P. per hour 

 against 2\ Ibs. consumed by ordinary steam-engines. About 



