WARMING AND VENTILATING OCCUPIED BUILDINGS. 313 



method of securing liealtbful ventilation as strong as desirable in occu- 

 pied buildings, and especially in the wards of large hospitals, or in those 

 of small hospitals capable of being warmed by an open grate, 



9. As regards those establishments where it would be necessary, un- 

 der special conditions, to employ mechanical methods of forcing in air, 

 it would always be well to aid their action by a strong draught, partic- 

 ularly affiecting those places from which exhalations are supposed to 

 arise. 



The latter case seldom occurs in establishments where ventilation 

 must be continually maintained ; the amount of air removed and intro- 

 duced remaining almost always constant. When, on the contrary, this 

 work must be frequently changed from one place to another in the same 

 building, and when the amount of air to be changed differs very greatly 

 from one day or hour to another, as is the case, for example, in Saint 

 George's Hall, Liverpool, where these amounts vary from 1 to 50, it 

 may become necessary, or at least advantageous, to assist the action of 

 the draught produced by heat, by that of a mechanical aj)paratus to 

 produce a sufficient motion in the air-supply pipes. 



These conclusions, based upon the discussion of a large number of 

 experiments made by several observers, have been accepted by the 

 hospital consulting committee of hygiene and medical practice, ap- 

 pointed by the secretary of the interior, under an imperial decree of 

 August 29, 1862. They apijly to ventilation of all occupied places, and 

 they serve as foundations for the special rules which we shall present. 



39. Influence of seasons. — It is important not to forget that, in the 

 winter, ventilation ma,y be secured directly and at the same time as 

 warmth. It is this, in particular, which renders warming by means of 

 fire-places in winter so healthful. But it is proper to repeat that this 

 natural ventilation, due to differences of temperature, which are usually 

 quite small, is essentially inconstant, and, therefore, liable to act alter- 

 nately in the reverse direction, which would often cause great trouble. 



The simple difference of internal and external temperature, and, con- 

 sequently, of the densities of the external and internal air, are then 

 capable of producing sufficient velocity in the receiving and discharging 

 channels to maintain the renewal of air in a proper manner. Thus is 

 obtained what is called natural ventilation. 



40. Amount of air to he changed every hour to ])reserve the healthful con- 

 dition of the room : 



Cubic feet. 

 Hospitals : 



For ordinary cases of sickness 2, 119-2, 472 



For surgical and lying-in cases 3, 532 



During epidemics 3, 709 



Prisons 1, 766 



Workshops : 



Ordinary occupations 2, 119 



Unhealthful occuj)ations 3, 532 



