XI 



EFFICIENCY OF GAS TRACTORS 



GAS tractors range in size from 12 to 110 b.h.p., and 

 from two and one half to fifteen tons in weight. The 

 brake horsepower ratings are usually placed closer 

 to the maximum load than for steam engines. This 

 is logical, since the engines should be rated at the load which 

 they will carry safely and economically. It is customary to 

 provide 10 to 20 per cent, of power over the rating in order to 

 protect the machine from overloading and the customer 

 from disappointment. The gas tractors are fairly well divided 

 by manufacturers into three classes. The first consists of 

 tractors of from 18 to 30 b.h.p., capable of handling three or 

 four plows in ordinary sod-breaking. The second is provided 

 with from 40 to 50 b.h.p., handling from five to seven plows in 

 heavy work. The largest class ranges from 60 to 75 b.h.p., 

 with the ability to pull from eight to ten plows under the same 

 conditions. A few have been made even larger than these, 

 but are not as yet sold so extensively as either the smaller 

 gas tractors or steam engines of large size. They will pull 

 ten or twelve breaking plows, comparing in power with 

 steam engines of 30 to 32 h. p., nominal rating. Recently 

 there have also been put on the market a number of small 

 outfits weighing from two to four tons, and having as low as 

 12 b.h.p. 



The indicated horsepower of gas tractors is seldom given 

 among the manufacturer's specifications. The brake horse- 

 power at full load is usually from 75 to 85 per cent, of the 



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