322 CRITICAL NOTICES OF NKW PUBLICATIONS. 



The examination of the circumstances which vary the quantity of 

 steam produced by heated metals, was so fully gone into in the expe- 

 riments of the Committee, and is so replete with numerical details, 

 that we cannot do it justice in our limited space for criticism. We 

 shall therefore barely state how these circumstances were varied, and, 

 referring our readers to the Report for all except the principal num- 

 bers, give the conclusions drawn by the Committee in their own words. 

 The experiments were made, first, by introducing drops of water into 

 bowls of iron and copper with different states of surface, of different 

 thicknesses, and heated to different temperatures ; then different quan- 

 tities of water, up to that of the entire capacity of the heated vessels, 

 under similar variations, and with the additional one of variation in 

 the means of communicating heat. The practical question immedi- 

 ately in view was to determine at what temperature of a metal, wa- 

 ter, thrown upon it in a limited quantity, will be most rapidly turned 

 into steam. Taking into consideration, of course, whether it is, or is 

 not, supplied with heat. 



" From the foregoing details may be deduced the following general conclu- 

 sions, which will be found of practical importance. 



" 1st. The vaporizing power of copper when supplied with heat, bj a bad 

 conductor or circulator, such as oil, increases with great regularity as the tem- 

 perature increases, up to a certain point, the water being supposed thrown 

 upon the copper surface, in small quantities. Copper flues, heated by air 

 passing through them, would be in this condition ir'left bare of water, and 

 then suddenly wet. This holds with copper 1-I6th of an inch thick, without 

 indication that a limit will be attained by a much more considerable thick- 

 ness. The temperature at which the metal will have the greatest vaporizing 

 power, is about 570** Fah. or about 230** below redness, according to Daniell. 



** The law of vaporization of small quantities of water, by a given thickness 

 of copper, is represented with singular closeness by an ellipse, of which the 

 temperatures represent the abscissae, and the times of vaporization the diffe- 

 rence between a constant quantity and the ordinates. 



" 2nd. The same power in thin iron, .04 (7-32nds) inch thick, increased re- 

 gularly, and was at a maximum, probably, at 510**. With thicker metal the 

 f>ower increases more rapidly at the lower temperatures, and varies very 

 ittle, comparatively, above 380**, with thicknesses exceeding |th, and less than 

 ^th of an inch; attaining a maximum at about 507** Fah. when the quantities 

 are small; rising to 550**, and much above, as the quantity of water is in- 

 creased relatively to the surface of the metal which is exposed. Quadrupling 

 the quantity of water, the entire amount being still small, nearly tripled the 

 time of vaporization at that maximum. 



"3d. When copper of l-16th of an inchin thickness, was supplied with 



mittee omitted no datum which might be of importance ; that they experi- 

 mented several times and with the same results, except that, on the last day 

 of trial, they were able to heat the steam more highly than on former days ; 

 and that a momentary decrease of elasticity from the injection of water into 

 the hot steam being aiways the result, the tem}ierature of the water from 

 which the steam was raised was not an element required in the general solu- 

 tion of the problem as attempted : and thus they were enabled to omit the 

 tables of results when the temperature of the water was correctly ascer- 

 tained, and give us only the results of that day's trial in which they had 

 pushed the experiment furthest. We are at a loss which most to value — 

 the scientific knowledge or the candour of the reviewer. 



