94 POWER AND THE PLOW 



great objection to this system is the large quantity of water 

 used and the necessity for frequent re-filling of the tank. 

 Another arises from the fact that in alkali districts the rapid 

 evaporation leaves behind a solution of increasing density 

 from which scale-forming material will be deposited. Unless 

 the screen is protected, dust from the atmosphere will add 

 further difficulties. In some enclosed coolers the spray of 

 water, or oil, is met by a current of air, generated by a fan. 

 The liquid being finely divided, a large area is exposed to the 

 air, hence cooling occurs quickly. 



In the closed type of radiator the air is separated from the 

 liquid medium by metal walls. On some small tractors are 

 found tubular or honeycomb radiators in connection with 

 fans, similar to the system used on most automobiles. Or- 

 dinarily, however, the radiating sections are not so delicate, 

 and a larger quantity of liquid is necessary in order to expose 

 sufficient area to the draft. In several cases the fan is dis- 

 pensed with, and the process simplified. The cooling of the 

 exhaust produces a partial vacuum and thus induces a strong 

 draft upward, which cools the liquid satisfactorily. In one 

 case the cooling arrangement is simply a huge tank, the water 

 being circulated by a pump, and the cooling being effected by 

 the evaporation of the water from the surface. 



A very effective method of cooling which may be used in 

 connection with some of the foregoing is that of using water 

 vapor with the mixture of the fuel and air to cool the cylinder. 

 In one tractor the steam which is formed in the radiator is 

 piped to the carbureter and inhaled with the fuel. In other 

 cases water is taken with the fuel through the carbureter and 

 vaporized in the cylinder. The amount of water is, of course, 

 slight, increasing automatically with the increase of heat 

 generated at the higher loads, or being cut out entirely at the 

 will of the operator. The latent heat of water is so high that 

 the evaporation of a very small quantity will prevent preignition 

 and the steam will have in addition a cleansing effect upon 



