Apkil 30, 1915] 



SCIENCE 



633 



of the remaining problems is but a matter 

 of brief period. Coineidently, splendid ad- 

 vances have been made in working out the 

 mechanical problems of ventilation. The 

 details of the installation of the boiler plant 

 have been refined with a resulting increase 

 in the efSciency of operation. New methods 

 of steam distribution, such as the vapor, 

 modulating and vacuum systems, have pro- 

 duced added comfort and economics. Tem- 

 perature control systems have been devised 

 and perfected to a point of reliability and 

 durability. The individual duct ventilating 

 system, providing air in the volumes and 

 of the exact temperature required by each 

 individual room under varying weather and 

 other conditions, has been developed. 

 Greater attention is paid to the diffusion 

 of the ventilating air. More attention is 

 now paid to the character of the installa- 

 tion and the materials used therein. Also 

 much emphasis is being placed upon the 

 measure of intelligence exercised in the 

 operation of the plant, upon which both 

 efficiency and economy depend. More 

 effort, however, still needs to be made in 

 these last two directions. Noisy heating 

 and ventilating plants may be considered 

 a thing of the past, for noise is indicative 

 only of lack of skill in design or installa- 

 tion. 



Ten years ago the mechanical efficiency 

 of the ventilating fan customarily used was 

 about 45 per cent. Now the best type of 

 fan (the multi-blade) has an efficiency of 

 65 per cent. This advancement results in 

 the saving of more than 30 per cent, of the 

 power expenditure for ventilation. The 

 efficiency of the driving device has also 

 been increased, although in a less degree. 



■Possibly the most interesting, important 

 and valuable recent addition to the equip- 

 ment of ventilating plants is that of the 

 air washer. Eeference to air washing is 

 made by Dr. D. B. Reid in his book on 



"Ventilation" published in London in 

 1844 but it is really a product of the last 

 ten years. Briefly it consists of a sheet- 

 metal chamber in which the air is passed 

 through a heavy mist and then through 

 baffles or eliminator plates by which the 

 air is so deflected that the entrained mois- 

 ture is removed. The base of the washer 

 constitutes a tank, into which the spray 

 water falls and from which it is drawn by 

 a centrifugal pump, usually motor driven. 

 The pump forces the water through pipes 

 and so-called nozzles which atomize the 

 water in the spray chamber of the washer. 

 The manufacturers of these washers cus- 

 tomarily guarantee the removal of 98 per 

 cent, of the dust in the air. Practically all 

 of the larger dust particles are removed 

 but there is always a residue of fine dust 

 which no washer will remove. In dry 

 windy weather when there is a great deal 

 of dust in the air, a large percentage of the 

 dust is removed, but when there is very 

 little dust in the air, as after a heavy rain, 

 a small percentage of the dust is removed. 

 Thus in Mr. M. C. Whipple's studies of the 

 air washer it was found that the dust re- 

 moval varied from 64 per cent, to 7 per 

 cent. Certain dusts are not, to an appre- 

 ciable extent, removed by the air washer. 

 A standard method of testing air washers 

 is needed and efforts are being made by the 

 American Society of Heating and Venti- 

 lating Engineers to work out this problem. 

 The best results obtained in artificial 

 humidiflcation have been through the( 

 medium of the air washer. By the use of 

 thermostatic devices an accurate control of 

 the degree of humidiflcation is obtained. 

 The use of the evaporating pan containing 

 a steam coil placed in the fresh-air chamber, 

 the coil being under thermostatic control, 

 also makes possible artiflcial humidiflcation, 

 but less satisfactorily. 



The air washer may also be used for air 



