634 



SCIENCE 



[N. S. Vol. XLI. No. 1061 



eooling. The evaporation of the water in 

 the spray chamber will result in a lowering 

 of the temperature of the air to the extent 

 of 75 per cent, or more of the difference 

 between the wet and dry bulb temperatures, 

 often amounting to 10 to 15 degrees and 

 sometimes to 18 to 20 degrees. This is due 

 to the fact that water can not be evaporated 

 without a supply of heat from some source, 

 and in this case the heat is taken from the 

 air. Considerable cooling can be done by 

 the use of the same water recirculated by 

 the pump and a greater degree of cooling 

 may be accomplished by a continual supply 

 of cold water. Purchased from the city 

 mains this would be expensive, but if 

 pumped from an artesian well the cost is 

 small. "Where a constant cooling effect is 

 desired, independent of weather conditions, 

 the use of a refrigerating plant in combina- 

 tion with the washer is necessary. The 

 water tank is then increased in size and 

 brine or ammonia coils, partially submerged 

 and partially subjected to the falling spray, 

 are installed. This is the most efficient 

 method of positive artificial cooling, and is 

 the most desirable method for ordinary 

 purposes. Unfortunately it is expensive to 

 install, involving approximately $300 to 

 $600 per thousand cubic feet of air cooled. 

 The cost of operation altogether depends 

 upon the nature of the plant of which it is 

 a part. If the plant is large, with exhaust 

 steam to spare for use in an absorption 

 refrigerating machine and the eooling water 

 used in connection with the refrigerating 

 plant may be used in the boilers and for 

 domestic purposes in the building, the cost 

 of operation is slight. Otherwise it may be 

 roughly stated that the cost of cooling ten 

 degrees during the summer is approxi- 

 mately equal to the cost of heating seventy 

 degrees during the winter. 



Cooling by evaporation of water alone 

 has the disadvantage of increasing the 



humidity, which is usually considered ob- 

 jectionable. But there is some evidence 

 that in hot weather the lower temperature 

 with higher humidity is preferred by 

 workers. Mr. J. I. Lyle quotes, among 

 others, an engineer who has done a great 

 deal of testing laboratory work, in which 

 the conditions were most exacting. He 

 writes : 



We can state that under the conditions shown 

 by the readings below, the inside condition with a 

 lower temperature, but a higher humidity, is more 

 pleasant than the outside condition with higher 

 temperature and lower humidity. 



He illustrated by a comparison of out- 

 side conditions of 90 degrees dry bulb, 80 

 degrees wet bulb and 65 degrees relative 

 humidity with inside conditions of 85 

 degrees dry bulb, 79 wet bulb and 77 per 

 cent, relative humidity. 



For ordinary ventilation work cooling at 

 the expense of an increased humidity has 

 been regarded as objectionable. It is said 

 to produce a moist "clammy" feeling. 

 Thus dehumidification becomes a part of 

 artificial cooling, and the most expensive 

 part, for the air must be cooled to that 

 temperature at which saturated air contains 

 the moisture necessary to give the desired 

 relative humidity in the air when reheated 

 to the ultimate temperature. 



The use of the air washer has become al- 

 most indispensable in many industries, such 

 as textile manufacturing, candy, macaroni, 

 photographic and film making and in some 

 processes of paper, tobacco, chemical, steel 

 and plumbing fixture manufacturing. 



Commercial considerations have done 

 much to develop the use of the air washer 

 in industrial fields. It is regrettable that 

 humane considerations have done much less 

 in this way in the general field of ventila- 

 tion. 



Possibly the most interesting study in 

 the mechanics of ventilation is that of the 



