PHENOMENA CONNECTED WITH CLOUDY CONDENSATION. 209 



pieveuted this heated air tVoiii cumiujj; to the jet its coudeusatioii was 

 dense. 



A slight alteration was then made in the arrangement. The jet was 

 now directed downward at the end of the horizontal pipe. By this 

 means the air heated on the pipe and nozzle was prevented from mixing 

 with the jet. The jet was directed at a small angle from the vertical 

 to prevent the hot air and vapor of the jet rising- to the nozzle. With 

 this arrangement the following was the resnlt: Up to a temperature of 

 40° tlie condensation was dense, and neither electricity nor the products 

 of combustion had any effect on the density; but when the temperature 

 rose to about 47° electrihcation began to have just a perceptible effect 

 in increasing the density. At about 48° the electricity had an easily 

 observed effect, and the products of combustion also had a slight effect. 

 At a temperature of 50° the jet had become decidedly thinner, and 

 both electricity and the products of combustion had a decided eff"ect 

 in increasing its density. When the temperature rose to 55° the jet 

 lost iis dense ai)pearance, and both electricity and the products of com- 

 bustion had a- very marked effect. 



It might be thought that by observing a steam jet in the open air we 

 could tell if the temperature of the air was above or below a certain 

 point. This however can only be done in a very rough way, as the 

 conditions are variable and not within our knowledge. We would 

 require to know the pressure of the steam and the degree to which 

 the air was heated bj^ the i)ipe. In a general way it may be stated 

 that in the open air a steam jet looks dense if the temperature be below 

 50°, and ordinary if abo^'e 55°. But it is often difficult to say what is 

 ordinary and what is dense condensation, unless the observations are 

 nuide carefully and by examining how close to the nozzle the particles 

 are visible. Of course, if we could electrify the jet or supply it with 

 the products of combustion, we could tell whenever the tem})erature 

 was over or under 47°. 



The sudden alteration in the appearance of the jet when supplied 

 with air at a temperature of 46° points to some change in the influences 

 in action in the condensing jet. The great increase in density can not 

 be due to an increase in the amount of vapor condensed, as the fall in 

 the temperature is slight. Further, it will be observed that the jet 

 has ceased to be influenced by electricity and by the products of com- 

 bustion. The onlj' explanation I could think of was that at the tem- 

 perature of the mixed cold air and steam some alteration had taken place 

 in the surface films of the water drops. The jet looked as if something- 

 came into action at that temperature which prevented the drops coa- 

 lescing when they came into collision, or what would amount to the 

 same thing, that at high temperatures there was no tendency for the 

 drops to recoil after impact, and that when the temperature fell this 

 proi)erty made its appearance and i)revented contact in the same way 

 as we have supposed the electrification does. 

 SM 93 U 



