146 TRANSACTIONS OF THE 



It will be seen, fig. 11, that one hub enters the other, conically, 

 and it will be perceived that the only joint which is subject to 

 pressure, is thus made in the most perfect manner, and most 

 securely held by the central bolt. This point, as well as the 

 outer one, is ground. 



Tho ordinary mode of setting, is to let it form a joint of the 

 upright exhaust pipe, so that the exhaust steam on leaving the 

 engine, passes in at the lower nozzle, spreads out in the lower 

 hemispherical cavity, passes on through the eighteen tubes of the 

 lower section into the central cavity, thence through the eighteen 

 tubes of the upper section into the upper cavity, and on through 

 the nozzle into the exhaust pipe. 



Or the direction of the steam may be reversed by taking it out 

 of the exhaust pipe by a branch pipe, and in at the upper nozzle, 

 draining out the water produced by condensation, at the bottom, 

 the lower nozzle being closed, and furnished with a drain cock. 

 This is sometimes the better plan. 



The course of the water, entering at the lower opening, filling 

 the space inside of the case, around and between the tubes, and 

 between the heads; and passing through the hub, around the 

 bolt, into the upper section, and out at the upper opening, is 

 seen at a glance. 



Nos. 1, 2 and 3, are made in a single section ; Nos. 4 to 8, in 

 two sections; and beyond that, they may be combined at pleasure. 

 They have been made in three and four sections, of the size of 

 those in No. 8, making, respectively heaters 50 and 100 per cent 

 larger than No. 8. 



The power of engine for which the respective sizes are suitable, 

 given in the second column, is calculated from a careful experi- 

 ment of the quantity of water heated in a given time, from SO'* 

 up to 200°; assuming an evaporation of 8 lbs. of water per pound 

 of coal, and 5 lbs. of coal per horse power per hour; or 40 lbs. of 

 water per horse power per hour. 



It is also assumed that the supply shall be regular. As the 

 feeding cannot be, in practice, entirely regular, and is often very 

 irregular, it is better to use a larger heater than is indicated in 



