Notes on Steam Boilers. 323 
amount of megass and wood used as fuel in efficient 
furnaces, tends to render the plain multitubular boiler 
very efficient here, and this considered with its low first 
cost, renders it perhaps more than others the boiler for 
a sugar estate, although in England, from the conditions 
of the water and fuel there, it is almost a curiosity. On 
arriving here, I found much uncertainty respeaing the 
necessity of Horizontal Steam Chests for both multitu- 
bular and compound boilers ; from what I have seen of 
multitubular boilers here the necessity of a horizontal 
steam chest arises from their being insufficient steam 
space in the boiler, thus leading to wasteful and danger- 
ous priming. 
It is a fa& that a boiler with tubes not higher than its 
centre line will give more satisfaaion than one with 
high tubes having a horizontal steam chest. It is 
evident that if an upward current exists in the medium 
through which the foreign particles are sinking they 
will move with a velocity which will be the difference 
between the velocity of the current of their downward 
tendency. If the upward current is more rapid than the 
rate of falling, the particles must be carried upward, and 
will be so carried as long as the velocity of the current 
is maintained. Now in the steam boilers the proportion 
which the free water surface bears to the power of the 
boiler varies very greatly, and the velocity with which 
the steam rises from the surface is not only inversely as 
the area of the free surface, but also inversely as 
1 the pressure ; while the viscosity is unaffeaed by the 
pressure. 
Now bearing in mind that a drop of water w __ inch 
f diameter falls at the rate of 0.067 per second, it is easy 
