282 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[August, 



previously proposed by divers aiilhors to represent tliut law, none of 

 which are applicable but in a limited extent of the scale ; but we are 

 surprised to find that he has made no mention of that proposed by Mr. 

 A. A. Momay in the second volume of our Journal, page 200, which 

 represents Dalton's experiments below 212", an3 those of the French 

 Academy up to 24 atmospheres, (beyond vvliich they did not extend) 

 within 2-43 degrees Fahr. at the latter limit, where a new formula, 

 proposed by the author of the present work, gives a difference of 

 10'26 degrees. 



In the reasoning through which he arrives at this formula, we rather 

 suspect that Mr. Kussell has fallen into the error he deprecates so 

 much in his preface — that o{ exhibiting the author at the expense of the 

 reader, though we think his parade of calculus only calculated to dazzle 

 the very ignorant, without being intelligible to the mathematician. 

 What, for instance, do the series a, B, y, and the equations !, e, (page 

 113) signify ? We confess they are above our comprehension, but 

 perhaps some more profound mathematician might be able to explain 

 their meaning, and to point out their connexion with the laws of tem- 

 perature and pressure, mentioned in the previous part of the para- 

 graph, and with each other. By some means, however, we are led to 

 the equation, (page IIG) 



'ogF 



which appears in an entirely different form from any other that has 

 been published, but which differs in fact from Tredgold's only in the 

 values of the constants ; it is, indeed, when freed from logarithms, 

 nothing more or less than the following: 



V 333 J 



6-42 



Mr. Mornay's formula alluded to above, possesses this great advan- 

 tage over the others, that it furnishes a very simple equation for find- 

 ing the elastic force of steam in terms of its density alone, which is 

 necessary in calculating the effect of steam used expansively in steam 

 engines. Regarding the density of steam Mr. Russell has given no 

 calculations at all, although, besides the formula just alluded to, one 

 has been proposed by Mr. Navier, and a modification of it employed 

 by the Count de Panibour in his Theory of the Steam Engine, published 

 in 1839; but there is in the 4th section a very comprehensive table of 

 the density of steam at different temperatures, by Gay-Lussac, as well 

 as an engraving and description of the simple and elegant apparatus 

 used by that philosopher, with his method of operating. 



The 5th section, 071 the application of our inowledge of the properties, 

 phenomena, and laws of steam to practical and economical purposes, is 

 interesting as far as it goes ; but, as we stated at the beginning of this 

 notice, the most important application, the Steam Engine, is published 

 in a separate volume. 



The article Steam Navigation might, with greater propriety, be 

 entitled "the Steam Navigation of Scotland and the United States," 

 the share of that part of Great Britain called England being represented 

 by the following paragraph : 



" To the talent of Mr. Maudslay of London, the present marine en- 

 gine owes the introduction of that high degree of precision in its con- 

 struction and details, which gives it so much durability and efficacy as 

 a machine." 



From the tenor of this article it would appear that the author was 

 utterly ignorant of the numerous steam boats with which the river 

 Thames is studded at all hours of the day, and some of which vie in 

 speed with the vaunted American steam boats, and that he knew of no 

 steam vessels which navigate the ocean with other than Scotch engines. 

 He does not say (is he ignorant of the fact?) that the Great Western, 

 with Maudslav's engines, makes better passages to New York than 

 the British Queen, with Napier's. The history of the progress and 

 present condition of the art, as here traced, thus bears reference only 

 to the two countries named above— Scotland and the United States; 

 it is, however, as such, interesting enough, but would be rendered 

 much more so, if combined with the history of the art in England. 



The following paragraph in page 268, taken in conjunction with the 

 omission of all mention of Maudslay's four cylinder engine, and with 

 the description of Humphreys' trunk-engine, accompanie<l by a wood 

 cut, in the preceding page, would corroborate the opinion that the 

 author had but a very limited knowledge of the state of Steam Navi- 

 gation in England. 



For a like purpose, oscillating cylinders have been user] with some measure 

 of success. Rotatory engines have been unsuccessfully tried. The reader 

 may now examine the vertical engines in the plates. 



We believe the only trunk-engine yet made is that of the Dartford, 

 which turned out a failure, while many steam boats now rucning on the 

 Thames are fitted with oscillating engines, among which are aome of 

 the swiftest boats on the river. 



We copy the following proof of the doctrine that the vacuum in a 

 condenser may be too good, or rather that any improvement in the 

 vacuum beyond a certain limit must be obtained at the expense of 

 more fuel than it is worth ; because it is not altogether without found- 

 ation, but, by reason of false notation, seems a tissue of absurdity and 

 contradiction. 



Let / = the caloric of water of 1". 



c = the constituent caloric of water in the state of steam. 

 p = the total force of steam in the boiler in inches of mercury ; 

 and j: = the elastic force of steam at the temperature of best condensation 

 which we seek to discover. 

 Then from the law which connects the elastic force of steam with tempera- 

 ture, as already determined in our treatise on Steam, it follows, that in the 

 case of maximum effect, or the temperature of best condensation, 



t X et 



— = — that is x= — 

 c e c 



now ff = 1000, and if the steam in the boiler be at 5 fb. above the atmosphere^ 

 or if e = 40 inches of mercury, and / = 1. 



40 



-=Iooo=»'^'' 



Again, if the steam be at 7 J lb. = 45 inches, 

 45 



1000 



= 0045 



Again, if the steam be at 10 tb. = 50 inches, 



50 

 ' = IO0O = «'»^ 



Hence, we find that the best elasticity or temperature in the condenaer 

 depends on the elastic force of the steam in the boiler. 



With steam of 5 %. in the boiler, the elasticity of maximum effect in the 

 condenser is at 93° of Fahrenheit, and the best vacuum in ihk barometer is 

 28. With steam of 7i tb. in the boiler, the elasticity of maximum effect in 

 the condenser is 95' of Fahrenheit, and the best vacuum in the barometer is 

 27'8. With steam of 10 lb. in the boiler, the elasticity of maximum effect in 

 the condenser is 97 , and the best vacuum in the barometer is 27a. In like 

 manner it would he found that with steam of 50 tb. in the boiler, worked 

 expansively, as in Cornwall, the best vacuum in the condenser would he about 

 26° on the barometer. 



Our first impression on reading this proof was that it was altogether 

 fallacious, and, as the calculation was not supported by reasoning, it 

 was not likely to convince us of the contrary; but, on consideration, 

 it seeming probable that the general proposition was true, although 

 Mr. Russell's equation was not the interpretation of a truth, we in- 

 vestigated the subject more closely, and found that this equation did 

 not represent the author's own opinion, but that x ought to stand for 

 the increment of elastic force due to the increment 7 of heat at the 

 temperature of most advantageous condensation, that c ought to repre- 

 sent the total quantity of caloric required to evaporate water from that 

 temperature, and not merely the amount of latent heat at 212°, and 

 that e should express, not the total pressure in the boiler, but the mean 

 effective pressure on the piston before the allowance for friction has 

 been deducted. The equation should therefore stand thus, retaining 

 X with the signification first assigned to it by Mr. Russell, and express- 

 ing by dif. X a very small difl'erence of elastic force, and by dif. t the 

 corresponding very small difference of temperature, 



dif.x__ df. t 

 e c 



the explanation of which is as follows : 



The first member expresses the ratio of an assumed small gain of 

 power to the total power exerted by the steam, and the second mem- 

 ber the ratio of the quantity of heat thereby abstracted from the feed 

 water (which must be restored in the boiler at the expense of a pro- 

 portionate quantity of fuel) to the total amount of heat requisite to 

 convert it into steam, or, which is the same thing, the ratio of the ex- 

 tra fuel to the total quantity used. Now it is obvious that, if these 

 two ratios are equal, that is, if the increase of power is in proportion 

 to the increase in the consumption of fuel, there is no gain of dutf, 

 and, of course, if the second member were greater than the first, the 

 result would be a diminution of duty. 



If we make the small difference of temperature = 1°, as Mr. Russell 

 has done, dtf. x will express the -increment of force due to an incre- 

 ment of 1° of temperature; and, if we suppose the best temperature 



