Abstract
In former report it was shown that in rooms where the amount of dusts infiltlated is always constant, a final density of dusts is determined by those amounts of produced, fallen and infiltrated dusts and further by the volume of air to be introduced into the room per hour and the total volume of the room. In this report it will be considered what amount of dusts are falling per hour in the room the density of dusts is always constant. For this consideration, it is supposed that the distributions of the size of dust particles will follow the normal probability distribution, and the falling velocity of particles is shown by Stokes' Law. On these suppositions a equation for accounts of the amount of dusts fallen on the unit area per hour is led by integrating the normal probability curve of size distribution. By the equation, the averge and the standard deviation of the particle-size distribution of dusts and specific gravity of particles determine the amount of bust particles fallen. But this result apploximatively equal to the result in the case that the size of particles is uniform. After those considerations the fact that the ratio of the amount of fallen dusts to total amount of floating dusts in tne room, is probably 0.1 per hour or least even in the calm condition, is found.
