372 EXPLANATION OF THE PLATES. 



metallic surfaces be diminished, the quantity of cold water or the capacity of the air- 

 pump, or both, should be increased to produce the same effect. 



" Having now described the five several apparatus the combination of which (within 

 proper proportions as hereinbefore described as regard the first three) constitute my 

 invention, I proceed again to define and explain the extent of my claims. I now 

 therefore state, I do not claim the exclusive use of any one of the five apparatus 

 herein described taken separately, some of them, if not all, having been used before, 

 nor indeed do I claim the use of any two of them, if unaccompanied by any or either 

 of the others, but I do claim as my invention the exclusive use of the threefold 

 combination of the sufficient quantity of metallic surfaces, the sufficient quantity of 

 cold water passing among them, and the sufficiently capacious air-pump as herein- 

 before fully described, whether the said threefold combination be used alone or com- 

 bined with the distilling apparatus and the steam saver, or either of them. I 

 also claim the exclusive right of combining the distilling apparatus and the steam 

 saving apparatus, or either of them, with the above mentioned threefold combination, 

 or even with the two first of them, videlicet, the metallic surfaces and cold water 

 passing among them, should a less air-pump be used. In witness whereof," &c. 



The advantages of Mr. Hall's patent engines over injection engines will perhaps 

 be best understood by his comparative statement of them. 



"COMPARISON BETWEEN INJECTION STEAM ENGINES AND SAMUEL HALL'S 



PATENT STEAM ENGINES. 



" 1. Injection engines, when applied to The patent engines effect a supply of 



steam navigation, comprise of necessity the purest distilled water to the boilers, 



the barbarous practice of supplying dirty by which they are always kept in a 



salt water to the boilers. perfectly clean state. 



2. In injection engines, the water in The patent engines having pure dis- 

 the boilers may become saturated with tilled water in the boilers, it boils at 212 

 salt, in which case it will not boil under or at 13 less temperature than salt water, 

 225 of temperature. and of course requires less fuel to convert 



it into steam. 



3. In injection engines, in order to pre- The boilers of the patent engines never 

 vent the water from becoming saturated require any blowing out, no matter how 

 with salt, a large quantity of boiling long the engines are in uninterrupted 

 water must be pumped out of the boilers, operation. 



or blown off, and replaced with cold water 



