68 POWER AND THE PLOW 



an average of 7.67 Ibs. Twenty-four public brake tests 

 show a mean of 7.78 Ibs.; sixteen plowing tests 7.08 Ibs., 

 and four hauling tests 7.4 Ibs.; or a mean of 7.42 Ibs. for 

 the forty-four tests. Single-cylinder engines show a range of 

 from 5.78 Ibs. to 9.97 Ibs.; and double-cylinder from 3.3 

 to 10.3, according to official reports. Conditions were such 

 however, as to arouse doubts as to the accuracy of such ex- 

 treme figures. By making enough assumptions one can com- 

 pare these data with those furnished by operators of eleven oil- 

 burning steam engines in California. These men report the 

 use of 9.4 gallons of water per gallon of oil. Assuming the oil 

 to be of 20 Baume and to contain 20,000 B.t.u. per pound, 

 they used 1990 B.t.u., in evaporating one pound of water. 

 The ordinary run of coal used contains not over 13,000 B.t.u. 

 per pound; hence 1700 to 1740 B.t.u. would be furnished per 

 one pound of water. 



The cost of operating a steam tractor varies even more 

 widely than that of operating the gas tractor. The various 

 conditions are fully covered in Bulletin 170, United States 

 Bureau of Plant Industry, from which the average performance 

 of steam tractors as shown in 1907 and 1908 can be ascertained. 

 The following quotation gives quite accurately what may 

 be expected of steam tractors taken as a class, except that the 

 great improvement in both engines and plows, even in the short 

 interval, has added greatly to the efficiency of outfits. In 

 addition, the rapid education of operators, the improvement 

 in other equipment for use with engines, and the tendency to 

 use the tractors for a longer period of time each year, would 

 all help to increase the performance and reduce overhead 

 charges. 



AVERAGE RESULTS WITH STEAM-PLOWING OUTFITS 



In view of the extreme variation in conditions encountered by individual 

 operators, any averages of results must be taken with due regard for local con- 

 ditions. The following table presents a summary of the data taken from re- 

 ports complete enough to give the desired information. These include results 



