294 On the Rapid Production of Steam, 



the more speed when the accumulated force comes to be added to 

 the regular supply. This might be the case if the excess were fur- 

 nished with no greater rapidity than the deficiency had occurred. 

 But whether we suppose the hot steam, or the hot metal, to furnish 

 heat of elasticity to the water which flows into the over heated boil- 

 ers, the supply will be obtained almost instantaneously ; — a few se- 

 conds, at most, being required to complete the operation of genera- 

 ting, from water of a boiling temperature, all the steam which the iron 

 of the boiler, even when red hot, is capable of producing. In order 

 to determine with some precision, what effect will actually be pro- 

 duced by the metal in such cases, I have performed a series of ex- 

 periments tending to show the relation between the quantity of steam 

 generated, the weight of the metal, the surface exposed, the time of 

 action and the period of greatest effect. The trials have not been 

 confined to rolled iron alone, but as the results must obviously be ef- 

 fected by the specific caloric of the metal, I have extended them al- 

 so to wrought iron in masses, to cast iron, copper, brass, silver and 

 gold. 



These experiments were, in part, performed during the months of 

 July and August last, when the temperature of the room seldom fell 

 below 80°. This circumstance may, in addition to the other pre- 

 cautions to avoid error in the results, assure us that the change of 

 temperature in the water, between two consecutive expei-iments, can- 

 not at any time have been sufficient to affect the quantity of vapor 

 generated, or the time employed in its production. In order to exhi- 

 bit an approximation to the actual state of the boiler, when in a con- 

 dition to receive hot water on intensely heated metal, and when, of 

 course, the whole excess of calorie would be employed in giving 

 the elastic form, and none in -raising temperature, I procured a cyl- 

 indrical vessel of tinned iron 19|^ inches deep, 7/^ inches in diame- 

 ter, and capable of containing 28/g lbs. of water at 60°. This was 

 furnished with a cover of the same material, and with a wire handle 

 like that of a bucket, for the convenience of suspending it to the 

 beam of a pair of scales. The sides and bottom were covered ex- 

 ternally with four successive folds of stout green baize, between each 

 two of which was a hatting of raw cotton, forming all together a 

 coat of an inch thick. The non-conducting character of this de- 

 fence may be inferred from the fact that fourteen pounds of water, 

 left in the vessel for fourteen hours, was cooled only from 2i2° to 

 115° or about 7° per hour, while the temperature of the apartment 

 was at 80° j and that in the following twenty five hours, the same 



