It will be seen that the water performs a complete circuit; it is taken from the box and passed through the coils; what is steam remains in the steam chamber, and what is not (if any) drops back into the box from where it started.  Hence it will be seen that a large surface is exposed to a small quantity of water, and in a way that it is entirely controllable.  All the engineer has to do to surcharge his steam, is to reduce the speed of the pump (which is independent of the main engine).  By raising the heat and quantity of water, any degree of elasticity can be given to the steam, and that, too, with the least amount of waste heat in giving a natural draft.  Hence the great economy of this boiler.

The next feature of this engine is, it has no wood work about it to perish with the heat and roughness of the streets.  All the wheels are wrought iron; and, as yet, these are the only ones that have stood a steam fire engine.  The frame is wrought iron; truck, on which the front wheel is hung, wrought iron.  The axles are cast steel.  The engine and pump is a double-acting piston pump direct, without any rotary motion; with a perfect balance valve, it is balanced at all times, and hence the engine remains quiet without blocking, when at work.  The engine is mounted on three wheels, which enables it to be turned in a very short space.

Many engines have been constructed by the Messrs. Latta for the fire companies, of different cities, and have been in successful competition with other engines; the farthest throw ever made by one of their first-class engines was 310 feet from a 1-5/8 inch nozzle; steaming time, starting from cold water, 3-1/2 minutes.

[Illustration:  Fig. 74 AMOSKEAG STEAM FIRE ENGINE.]

Fig. 74 is a representation of one class of steam fire engine, as built by the Amoskeag Manufacturing Company, at Manchester, N.H.  The boiler is an upright tubular boiler, of a peculiar construction, the patent right to which is vested in the Amoskeag Manufacturing Company.  This boiler is very simple in its combination, and for safety, strength, durability, and capacity for generating steam is unsurpassed.  No fan or artificial blower is ever used or needed, the natural draft of the boiler being always sufficient.  Starting with cold water in the boiler, a working head of steam can be generated in less than five minutes from the time of kindling the fire.  The engine “Amoskeag,” owned by the city of Manchester, has played two streams in three minutes and forty seconds after touching the match, at the same time drawing her own water.  The boilers are made and proved so as to be safely run at a steam pressure of 140 to 150 lbs. to the square inch; but the engines are constructed so as to give the best streams at a pressure of about 100 lbs. to the square inch, and for service at fires a steam pressure of about 60 lbs. to the square inch is all that is required.