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A PRACTICAL TREATISE 
 
 ON 
 
 WARMING BUILDINGS 
 
 BY 
 
 HOT WATER; 
 
 AND 
 
 AN INQUIRY INTO THE LAWS OF RADIANT AND 
 CONDUCTED HEAT. 
 
 TO WHICH ARE ADDED, 
 
 REMARKS ON VENTILATION, 
 
 AND ON THE 
 
 VARIOUS METHODS OF DISTRIBUTING ARTIFICIAL HEAT, AND THEIR 
 EFFECTS ON ANIMAL AND VEGETABLE PHYSIOLOGY. 
 
 BY 
 
 CHARLES HOOD, F.R.A.S. 
 
 ILLUSTRATED BY NUMEROUS WOOD-CUTS. 
 
 LONDON: 
 WHITTAKER & Co. AVE MARIA 
 
 1837. 
 
 LANE. 
 
LONDON : 
 GILBERT & RIVINGTON, PRINTERS, 
 
 ST. John's square. 
 
PREFACE. 
 
 A NATURAL inclination for philosophical inquiries, 
 first led me to investigate the principles of the 
 invention for heating buildings by the circulation of 
 hot water ; and the many favourable opportunities 
 that have occurred for proving the accuracy of my 
 theoretical views, have encouraged me to persevere 
 in the investigation. 
 
 Frequent applications having been made to me, 
 by persons who were aware that the subject had 
 engaged my attention, to recommend to them a 
 practical treatise on its principles and application, 
 the utility of such a work, in forwarding the progress 
 of the discovery, became obvious. And finding that 
 nothing relating to the invention had hitherto been 
 published, except a few scattered and unimportant 
 notices, it appeared probable that the materials I 
 possessed might form a treatise which would be 
 
 A 2 
 
iv 
 
 PREFACE. 
 
 useful, not only in showing the practical application 
 of the invention, but also in explaining the scientific 
 principles upon which the various effects depend. 
 The following pages are therefore offered, in the 
 hope of supplying the desideratum. 
 
 The different parts of the subject have been 
 arranged, as far as possible, under distinct heads. 
 The primary object has been to explain the principles, 
 in a manner perfectly clear and intelligible to such 
 as are unacquainted with those branches of physical 
 science on which the philosophy of the invention is 
 based : and, while endeavouring to remove the 
 erroneous notion, which is entertained by some 
 persons, that a certain degree of danger is insepar- 
 able from the plan, to show that danger can occur 
 only through a misapplication of the principles. 
 
 In order to pursue the inquiry in a popular 
 manner, all abstruse calculations and scientific tech- 
 nicalities have been, as much as possible, avoided ; 
 and the most simple definitions the subject would 
 admit of have been adopted, as far as is consistent 
 with perspicuity. 
 
 The Rules, Calculations, and Tables, which are 
 given in the body of the work, have, nearly all, been 
 constructed expressly with reference to the present 
 inquiry; and the Tables given at the end of the 
 volume are compiled from the best authorities : the 
 whole comprising, it is hoped, all the information 
 which the subject requires. 
 
PREFACE. 
 
 V 
 
 In extenuation of any omissions or errors which 
 may be found, it should be borne in mind that, 
 hitherto, no attempt has been made to give a com- 
 prehensive view of this invention. The increasing 
 attention of the public to the subject, however, ren- 
 ders the present time the most proper for the publi- 
 cation of such a treatise as the one now offered : 
 and though probably much remains to be disco- 
 vered relating to the invention, the communication 
 of what is already known is the surer way of ex- 
 tending the sphere of its utility, than by waiting 
 until its principles shall be more fully revealed by 
 time, in the hope of producing a more complete 
 work. But although no excuse is thus intended 
 to be offered for any errors, other than such as 
 are trivial and unimportant, if any omissions be 
 found, the plea may be urged, and will, perhaps, be 
 admitted — Bis dat qui cito dat. 
 
 To conclude these prefatory remarks : it may 
 be observed that in pointing out, and freely com- 
 menting on the erroneous principles which have, 
 in some instances, been both theoretically and 
 practically promulgated by others, it is under the 
 impression that such errors, carrying with them in 
 general considerable plausibility, might, if uncon- 
 futed, lead not only to inconvenience, but even to 
 danger; more particularly, as, on account of their 
 emanating from men of ability, others may also be 
 liable to fall into similar mistakes. However invi- 
 
Vi PREFACE; 
 
 dious, therefore, the task of pointing out sucli errors 
 may seem, it appeared to be necessary, when writing 
 on this subject, not only to exhibit what were con- 
 sidered to be the true principles, but also to show 
 where erroneous notions have been adopted. This 
 must be the apology for the freedom with which the 
 opinions and inventions of others are descanted on 
 in the following pages ; and, as these are not the 
 production of an inventor, who is expatiating on 
 the advantages of his own particular plan, they 
 will, it is hoped, be found a candid inquiry into the 
 merits of the various descriptions of apparatus which 
 are brought under consideration, pointing out their 
 philosophical principles, and displaying their utility 
 in a practical manner. 
 
 C. H. 
 
 Em^l Street^ Blackfriars, 
 September, 1837. 
 
CONTENTS. 
 
 PAGE 
 
 Introduction 1 
 
 CHAPTER I. 
 
 On the cause of circulation of the water, and its consequences 7 
 
 CHAPTER II. 
 On the application of the principles 24 
 
 CHAPTER III. 
 On the proportionate sizes of various parts of the apparatus 5 1 
 
 CHAPTER IV. 
 
 On permanence of temperature, depending on the form and 
 size of the boiler and pipes 57 
 
 CHAPTER V. 
 
 On the size and construction of furnaces 75 
 
 CHAPTER VI. 
 On the laws of heat 82 
 
 CHAPTER VII. 
 Experiments on cooling 100 
 
viii 
 
 CONTENTS. 
 
 CHAPTER VIII. 
 
 PAGE 
 
 On the application of the laws of heat, to determine the 
 proper size of an apparatus for heating any description of 
 
 building 108 
 
 CHAPTER IX. 
 On peculiar modifications of the hot- water apparatus . .127 
 
 CHAPTER X. 
 
 General application and summary 155 
 
 CHAPTER XI. 
 On ventilation 169 
 
 CHAPTER XII. 
 On the various methods used for distributing artificial heat. 188 
 
 Tables, &c 205 
 
 Index 213 
 
 ERRATA. 
 
 Page 35, line 2 of note, /or " also directly" read ** the friction directly." 
 — 89, — 11, /or " (a'— 1)" read " (a'— 1)." 
 
A 
 
 PRACTICAL TREATISE, 
 
 &c. 
 
 INTRODUCTION. 
 
 The practice of employing hot water, circulating 
 through iron pipes, for diffusing artificial heat, has 
 now become so general, that its merits are acknow- 
 ledged as an invention of utility. The last twelve 
 years, though they have not actually been witness 
 to the discovery of the plan, have, at least, revealed 
 nearly all that is known respecting its practical 
 application ; for, previously, the range of its opera- 
 tion was confined rather to a few cases of expe- 
 riment, than extended to any general or useful 
 purposes. 
 
 It can scarcely excite surprise, that prejudices 
 should formerly have existed against this invention, 
 while its merits and its principles were alike imper- 
 fectly known. Even at the present time they are 
 
 B 
 
2 
 
 INTRODUCTION. 
 
 but partially understood ; and, therefore, to investi- 
 gate these two subjects, is the proposed object of 
 the present treatise, with the view of facilitating 
 its application, and extending the sphere of its 
 utility. 
 
 There is scarcely any branch of science or of art, 
 in which an acquaintance with the laws of Nature 
 does not enable us to derive greater advantages in 
 its application, than we could otherwise possess. 
 Although it is true that we are still ignorant of the 
 more subtile agents which exist in the vast chain 
 of causation, the laws which regulate the various 
 phenomena of nature, are sufficiently known to 
 afford the most beneficial assistance to every branch 
 of the arts and sciences: and the most recon- 
 dite of scientific discoveries, as well as the most 
 valuable inventions and improvements in the 
 arts, are not more demonstrative of the truth of 
 this assertion, than are those of the most simple 
 characters. 
 
 For an illustration of the utility of this know- 
 ledge, we may refer to the law of gravity ; not only 
 because it is, of all natural phenomena, the most 
 constant in its operation, and the most universal 
 in extent, but because its influence is closely con- 
 nected with the present subject of inquiry. 
 
 That all falling bodies gravitate with the same 
 velocity, and, therefore, descend through a certain 
 definite space in a given time, is, we know, an effect 
 
INTRODUCTION. 3 
 
 of which gravity is the cause. It is on the operation 
 of this invariable law, that many of our most valu- 
 able inventions depend. Its influence is equally 
 exerted on all objects ; as well the most dissimilar, 
 as the most alike ; as well the most mighty, as the 
 most minute. It is from this cause that we obtain 
 the unerring action of our pendulums and clocks ; 
 and it is by this also we obtain the circulation of 
 hot-water, with which we warm our dwellings. But 
 by a knowledge of the cause of these effects, of the 
 extent of its operation, and of the laws by which 
 it acts, we can, by varying the circumstances of a 
 gravitating body, alter also the velocity of its de- 
 scent. And we accomplish this by bringing other 
 causes into operation, which modify the result, not- 
 withstanding the immutability of the laws of gravity. 
 Thus, we can modify and subject to our will, one of 
 the most constant and universal agents in Nature, 
 by a knowledge of the physical laws. 
 
 The study of the laws which govern natural phe- 
 nomena, — which in all cases are so simple, so beau- 
 tiful, so perfect, — is, therefore, one of the most 
 fruitful sources of inquiry which the mechanician 
 can pursue. Without it all his plans will either be 
 modified copies of existing inventions, or they will 
 degenerate into wild speculations, unsupported on 
 any reasonable foundation. 
 
 This is particularly observable in the case before 
 us. The numerous failures which have occurred 
 
 B 2 
 
4 
 
 INTRODUCTION. 
 
 in the practical application of the invention of 
 heating buildings by the circulation of hot water, 
 are all distinctly roferrible to the want of this kind 
 of knowledge, and not to the object aimed at being 
 itself unattainable. But whenever the physical 
 laws are intended to be employed as the principal 
 agents in producing any mechanical effect, it is an 
 indispensable condition that simplicity of action be 
 kept in view. While it may further be observed, 
 that the endeavours to trace and elucidate the 
 operating causes of the various phenomena, which 
 occur in the course of practical experiments, are the 
 surest means of facilitating original discoveries, as 
 well as of promoting new adaptations of recognised 
 principles. 
 
 The origin of the invention of employing hot 
 water for diffusing artificial heat, appears to be hid 
 in considerable obscurity. It is not improbable 
 that, similar to many other discoveries, it has been 
 evolved at various periods from the Alembic of Time. 
 It seems, in one instance at least, to have been used 
 in France about sixty years since. After fading 
 from recollection for a space of about forty years, 
 it appears to have been re-invented by the Marquis 
 de Chabannes, and subsequently by Mr. Bacon and 
 Mr. Atkinson. And it was the latter, who, un- 
 doubtedly, first gave to the apparatus the arrange- 
 ment, under which it is now generally used in its 
 most simple form. 
 
INTRODUCTION. 
 
 5 
 
 The variations since made in its more complicated 
 arrangements, appear to have been very gradually 
 adopted. Each time that an apparatus has been 
 erected, the experimentalist has deviated in some 
 small degree from the model of that which pre- 
 ceded ; apparently afraid of venturing on too great 
 a variation, yet requiring, from contingent circum- 
 stances, some alteration of its form and application. 
 This mode of proceeding, though natural v^hile 
 the principles were not thoroughly understood, has 
 frequently led to both inconvenience and loss, in 
 consequence of the numerous failures to which it 
 has given rise, by unintentional deviations from the 
 principles. In the present attempt to elucidate the 
 subject, it will however be shown, that success 
 needs not be uncertain, provided only, that the 
 laws of physics be justly applied and strictly 
 adhered to. 
 
 Neither the capabilities of this method of warm- 
 ing, nor the various useful purposes to which it is 
 applicable, are at present fully appreciated. There 
 are no buildings, however large, to which it cannot 
 be advantageously adapted, nor any that present 
 insurmountable difficulties in its practical applica- 
 tion. It is an invention only yet in its infancy, 
 but which gives promise of a maturity that will 
 confer the greatest advantages w^here its employ- 
 ment is the most extensive. 
 
 Its merits, however, will best appear by the 
 
6 
 
 INTRODUCTION. 
 
 plainest statements of facts. We shall proceed, 
 therefore, at once, to the main object which has 
 been proposed ; an investigation of the principles 
 of this invention, as applied to the warming of 
 buildings. 
 
CHAPTER I. 
 
 Cause of Circulation of the Water — Force of Gravity — Pressure 
 of Water — Effect produced on the Circulation by increased 
 Height of the Pipe. 
 
 Art. 1. In endeavouring to explain the princi- 
 ples of the various forms of apparatus in which hot 
 water, circulating through iron pipes, is employed 
 as a means for distributing artificial heat, the first 
 object should be to point out, as clearly as possible, 
 the power which produces circulation of the water ; 
 for without a clear perception of this part of the 
 subject, there will always be an uncertainty as to 
 the results which will obtain, when any departure is 
 made from the most simple form and arrangement 
 of the different parts of the apparatus. It is this 
 circulation which causes all the water in the appa- 
 ratus to pass successively through the boiler, and 
 then communicates the heat that is thus received 
 from the fuel, to the various buildings or apartments 
 which it is designed to warm. Without this cir- 
 culation, those parts of the apparatus which are 
 remote from the fire would not receive any heat ; 
 
8 
 
 CAUSE OF CIRCULATION 
 
 because water is so bad a conductor, that it is only 
 when there exists perfect freedom of motion among 
 its particles, that it acts at all as a conductor of 
 heat, so far, at least, as regards any practical and 
 useful effect. It is in a complete and perfect circu- 
 lation, therefore, that the efficiency of a hot water 
 apparatus depends, and that the greatest amount 
 of heat is obtained by it from a given quantity of 
 fuel. 
 
 2. The only treatise hitherto published, in which 
 any attempt has been made to explain the cause of 
 circulation of the water in this description of appa- 
 ratus, is Mr. Tredgold's work on heating by steam ; 
 and the effect is there referred entirely to an erro- 
 neous cause. In the Appendix to that work, the 
 cause of motion is thus explained. " If the vessels 
 A, B, and pipes, be filled puj. 
 with water, and heat be 
 applied to the vessel a 
 the effect of heat will 
 expand the water in the 
 vessel A, and the surface will, in consequence, rise 
 to a higher level a, d, the former general level 
 surface being b. The density of the fluid in the 
 vessel A will also decrease in consequence of its 
 expansion ; but as soon as the column c, d (above 
 the centre of the upper pipe) is of a greater weight 
 than the column <?, motion will commence along 
 the upper pipe from a to b, and the change this 
 
OF WATER. 
 
 9 
 
 motion produces in the equilibrium of the fluid, will 
 cause a corresponding motion in the lower pipe from 
 B to A." 
 
 3. Now it is certain that this theory will not 
 account for the circulation of the water, under all 
 circumstances, and every variety of form, of the 
 apparatus ; and as the cause of motion must be the 
 same in all cases, any explanation which will not 
 apply universally must necessarily be erroneous. 
 Were this the true cause of motion, there would be 
 no difficulty in obtaining a circulation in all cases ; 
 for, according to this reasoning, whenever the level 
 of the water is higher in the boiler than in the 
 pipes — or even if an upright pipe were placed on 
 the top of a close boiler, by which the pressure on 
 the surface would be increased, — the water must, of 
 necessity, circulate through the pipes. On the 
 other hand, if this hypothesis were correct, the water 
 in an apparatus, constructed as in the following 
 figure, would not circulate at all. 
 
 4. Suppose the apparatus fig. 2, to be filled with 
 cold water, and the two stop-cocks g, to be closed: 
 on applying heat to the Fig. 2. 
 
 bulk, and a part of it v_^i^"^=^ ^ 
 will flow through the small waste pipe a;^ which is so 
 placed as to prevent the water rising higher in the 
 vessel A, than the top of the vessel b. The water 
 
 vessel A, the water it 
 contains will expand in 
 
10 
 
 CAUSE OF CIRCULATION 
 
 which remains in the vessel a, after it has been 
 heated, and a portion of it has passed through the 
 waste-pipe will evidently be lighter than it was be- 
 fore, while its height will remain unaltered. Suppose, 
 now, the two cocks g, to be simultaneously opened ; 
 the hot water in the boiler a will immediately flow 
 towards b through the upper pipe, and the cold 
 water in b will flow into a through the lower pipe ; 
 although, by the above mentioned hypothesis, unless 
 the water in the vessel a, above the pipe c, were 
 heavier, or rose to a higher level than the water in 
 the vessel b, no circulation could take place. In 
 this case, therefore, we must find another explana- 
 tion of the cause of motion. 
 
 5. The power which produces circulation of the 
 water, will be found to arise in a different manner 
 to what is here stated ; for we see that this reason is 
 insufficient to account for the effect, even in one of 
 the simplest forms of the apparatus. 
 
 6. In order to explain this, let us suppose heat to 
 be applied to the boiler a, fig. 2. A dilatation of 
 the volume of the water takes place, and it becomes 
 lighter ; the heated particles rising upwards through 
 the colder ones, which sink to the bottom by their 
 greater specific gravity, and they in their turn 
 become heated and expanded like the others. This 
 intestine motion continues until all the particles 
 become equally heated, and have received as much 
 heat as the fuel can impart to them. But as soon 
 
OF WATER. 
 
 11 
 
 as the water in the boiler begins thus to acquire 
 heat, and to become lighter than that which is in 
 the opposite vessel b, the water in the lower hori- 
 zontal pipe d, is pressed by a greater weight at z 
 than at j/, and it therefore moves towards a with a 
 velocity and force equal to the difference in pressure 
 at the two points y and z\ The water in the upper 
 part of the vessel b would now assume a lower level, 
 were it not that the pipe c furnishes a fresh supply 
 of water from the boiler to replenish the deficiency. 
 By means of this unequal pressure on the lower pipe, 
 the water is forced to circulate through the appa- 
 ratus, and it continues to do so as long as the water 
 in B is colder, and therefore heavier, than that which 
 is in the boiler; and as the water in the pipes is 
 constantly parting with its heat, both by radiation 
 and conduction, while that in the boiler is as con- 
 tinually receiving additional heat from the fire, an 
 equality of temperature never can occur ; or else if 
 it did, the circulation would cease. 
 
 (7.) We see, then, that the cause of the circula- 
 
 ^ To any person unacquainted with the science of Hydrostatics, 
 this may probably appear erroneous ; because the quantity of 
 water contained in a is much greater than that in b. It is, 
 however, one of the first laws of Hydrostatics, that the pressure 
 of fluids depends for its amount on the height of the fluid only, 
 and is wholly irrespective of the bulk, or actual quantity of fluid: 
 therefore, a pipe which is not larger than a quill, will transmit 
 the same amount of pressure, as though it were a foot, or a yard, 
 in diameter, provided the height be alike in both cases. (See 
 Art. 16.) 
 
12 
 
 INCREASED VELOCITY 
 
 tion is the unequal pressure on the lower pipe of 
 the apparatus ; and that it is not the result of an 
 alteration which takes place in the level of the 
 water, as has been erroneously supposed. Indeed, 
 the truth of this appears so plain, that it would 
 scarcely require explanation at such a length, were 
 it not that false opinions in this matter appear to 
 have led to many errors in practice. 
 
 (8.) As the circulation is caused by the water in 
 the descending pipe being heavier than that which 
 is in the boiler ; it follows, as a necessary conse- 
 quence, that the colder the water in the descending 
 pipe shall be, relatively to that which is in the 
 boiler, so much the more rapid will be its motion 
 through the pipes. In such an arrangement of 
 pipes as fig. 3, the wa- Fig 3. 
 
 ter in the descending 
 pipe e f, having to tra- 
 vel farther before it 
 descends to the lower 
 part of the boiler, than when the pipes are arranged 
 as in fig. 2, it will of course be colder at the time of 
 its descent, in the case, fig. 3, than in fig. 2, and 
 therefore the circulation will be more rapid. The 
 height of the descending pipe is supposed to be 
 alike in both cases ; because c d and e f, are, toge- 
 ther, equal to a b. 
 
 (9.) Some persons have imagined that if the pipes 
 be inclined, so as to allow a gradual fall of the water 
 
OF CIRCULATION. 
 
 13 
 
 in its return to the boiler, additional power is 
 gained ; as, for instance, by inclining the lower pipe 
 of fig. 3, so as to make the part e lower than d, and 
 then reducing the vertical height of the return pipe 
 e f. This, at first, appears very plausible, particu- 
 larly with regard to some particular forms of the 
 apparatus ; but the principle is, in fact, entirely 
 erroneous. The author of the Appendix to Tred- 
 gold's work, already quoted, in consequence of 
 adopting the erroneous hypothesis, that the motion 
 of the water commences in the upper pipe instead 
 of the lower one, as already described, appears to 
 recommend an inclination being given to the pipes 
 in this manner ; and he has described an apparatus 
 that he erected, to which a fall of four feet was 
 given to the water in this manner. 
 
 This error appears to arise from treating the sub- 
 ject as a simple question of hydraulics, instead of a 
 compound result of hydrodynamics. But in order 
 to ascertain what is the effect of thus inclining the 
 pipes, let us suppose an extreme case. 
 
 (10.) It is evident that the farther the water 
 flows, the colder does it become. It must therefore 
 be hotter at a (fig. 4) than it is at b, and hotter at 
 
 Fig. 4. 
 
14 
 
 EFFECTS OF GRAVITY. 
 
 B than c, and so on. Let us, now, suppose any 
 arbitrary number to represent the specific gravity of 
 the water at a ; say, for instance, -94. The water 
 at B, in consequence of having flowed farther and 
 therefore become colder and heavier, will be, we 
 will suppose, of the specific gravity of '95 ; at c, 
 for the same reasons, it will be '96, and so on to f, 
 where, from having run the greatest distance from 
 the boiler, it will be the heaviest of alP; and the 
 sum of all these numbers represents the pressure at 
 F. But had the pipe, instead of inclining gradually 
 from the boiler, continued on a level to as repre- 
 sented by the dotted lines, the water would have 
 been as' cold, and therefore as heavy, at a, as, by the 
 former arrangement, it is at f, and therefore its 
 specific gravity would be the same, namely, '99. 
 Now, as the pressure of water is as its vertical 
 height, by dividing the vertical pipe, a^f, in the same 
 manner as we have done with the inclined pipe, we 
 shall have a, c, d, e,/l each equal in altitude to 
 the corresponding divisions of the inclined pipe ; 
 and as the specific gravity of each division is equal 
 to '99, the total number representing the sum of 
 all these, will show the pressure at the point We 
 shall hence find the pressure of the vertical pipe 
 
 ^ The real specific gravities could not conveniently be used in 
 this illustration, as they would require several decimal places of 
 figures. See Table IV. 
 
 15 
 
EFFECTS OF GRAVITY. 
 
 15 
 
 compared to the inclined pipe, will be as 5*94 is to 
 
 (11.) It is therefore evident there must be a 
 considerable loss on the effective pressure, by mak- 
 ing the pipe to incline below the horizontal level. 
 Nor can this loss be compensated in any manner ; 
 for the total height being the same, whether the 
 water descends through a vertical or through an 
 inclined pipe, the force of gravity will only be equal 
 to the mass of matter. And as there is actually 
 more matter in a pipe filled with cold water than in 
 a similar pipe filled with hot water, the gravitating 
 force will be inversely proportional to the tempera- 
 ture; that is, it will be less in proportion as the 
 temperature of the water is greater. There must 
 therefore, under all circumstances, be a positive loss 
 of effect by inclining the pipe in the manner stated^. 
 
 (12.) In such a form of apparatus as fig. 3, there 
 would be no circulation of the water, unless some 
 plan were adopted by which the air would be dis- 
 
 ^ If the strict analogy were carried out, the difference ought 
 to be greater than is here represented ; because it is evident that 
 instead of a, b, c, d, etc., being each of equal density, b will be 
 heavier than a, and c heavier than b, and so on ; but the illustra- 
 tion, as now given, will be sufficient to show the principle. 
 
 ^ It must not be supposed that this reasoning at all applies to 
 any case of pure hydraulics. If the question were only as 
 regards a fluid of uniform temperature, then the greatest effect 
 would be obtained by using an inclined pipe ; but the fluid, 
 which we are now regarding, is one of a varying density and 
 temperature, which materially alters the conditional results. 
 
16 
 
 AIR VENTS. 
 
 lodged from tlie pipes, and a ready escape provided 
 for it. Nothing is more necessary to be attended 
 to than this ; for, in the more complicated forms of 
 the apparatus, the want of an efficient means of 
 discharging the air has been the cause of numerous 
 failures. Suppose we require the apparatus fig. 3 
 to be filled with water ; by pouring it in at the 
 boiler, the lower pipe will of course be filled first ; 
 and the water will then gradually rise higher in the 
 boiler until it partially fills the upper pipe. At last 
 the orifice of the pipe ^ will become full, and the 
 air which is in the pipe, being thus prevented from 
 escaping, will be forced towards c by the weight of 
 water behind it ; and if the quantity of air be suffi- 
 ciently large, it will entirely prevent the junction of 
 the water at c, and cut off the communication be- 
 tween the two pipes. If an opening be now made 
 in the pipe at c, the air will immediately escape, it 
 being forced out by the greater density of the water ; 
 and, therefore, either a valve or a cock must be 
 placed there, to allow of its discharge ; for other- 
 wise no circulation of the water can ensue. As 
 water, while boiling, always evolves air, it is not 
 sufficient merely to discharge the air from the pipes 
 on first filling them with water, because it is conti- 
 nually accumulating : and in many instances, particu- 
 larly with a close-topped boiler, it is desirable to have 
 the air vent self-acting ; either by using a valve, or a 
 
AIR VENTS. 
 
 17 
 
 small open pipe : in others a cock will be found 
 most convenient. 
 
 13. The size of the vent is not material, as a 
 very small opening- will be sufficient to allow the 
 air to escape. For the rapidity of motion in fluids, 
 being inversely proportional to their specific gravi- 
 ties, as water is 827 times more dense than air, an 
 aperture which is sufficiently large to empty a pipe 
 in 14 minutes if it contained water, would, if it 
 contained air, empty it in about one second. Air 
 being so very much lighter than water, it is of 
 course necessary that the vents provided for its 
 escape be placed in the highest part of the appa- 
 ratus, for it is there it will always lodge ; and some- 
 times it will be found necessary to have several 
 vents in different parts of the apparatus. 
 
 Though it is perfectly easy, as far as the mere 
 mechanical operation is concerned, to provide for 
 the discharge of the air from the pipes, it requires 
 much consideration and careful study to direct the 
 application of those mechanical means to the exact 
 spot where they will be useful. The subject will, 
 therefore, be again adverted to in a subsequent 
 chapter, when we have investigated the principles 
 of the apparatus in some of its more complex forms 
 of arrangement. 
 
 14. The plan of the boiler and pipes which 
 has been given in the preceding figures, is applicable 
 to comparatively but few purposes : for, in conse- 
 
 c 
 
18 
 
 CLOSE BOILERS. 
 
 quence of the boiler being open at the top, the pipes 
 must be laid level with it, otherwise the water 
 would overflow. When the pipes are required to 
 rise hierher than the ^' 
 
 vantages : for the higher we make the ascending 
 and descending pipes, the more rapid is the circu- 
 lation of the water. This consequence necessarily 
 results from the principles already explained ; be- 
 cause, as motion is obtained in consequence of the 
 difference in weight of the ascending and de- 
 scending columns of water, the greater the height 
 of these columns, the greater must be the differ- 
 ence in their weight, and therefore the greater must 
 be the force and velocity of motion. 
 
 15. The advantages which may be derived from 
 an increased height in the ascending pipe, cannot 
 however be applied in an unlimited manner ; be- 
 cause it might lead to inconvenience, and even be 
 attended with some degree of danger to the appa- 
 ratus, if the increased height were not regulated by 
 certain rules, and these, when ascertained, applied 
 with judgment. 
 
 boiler, the latter must H 
 
 B 
 
 be closed at the top, j \ 
 and the pipes can then j j 
 be carried upwards to j \ 
 any required height, i i 
 This arrangement pos- * 
 sesses considerable ad- 
 
PRESSURE OF WATER. 
 
 19 
 
 16. The pressure produced by water is calculated 
 by its columnar height, reckoned from the bottom of 
 the vessel in which it is contained. Whether the 
 vessel be open at the top and very deep, or closed 
 at the top and very shallow, but with a pipe attached 
 to the top, like the boiler and pipe a b, %. 5, the 
 pressure will be exactly alike in either case, if the 
 height be similar ; notwithstanding the quantity of 
 water may be 10 times, or 100 times, larger in the 
 one case than the other. Neither is the pressure 
 increased, however large may be the diameter of the 
 pipe which is used ; nor is it lessened if the pipe be 
 inserted at the side of the boiler, as in the dotted 
 lines y fig. 5, instead of being placed on the top. 
 
 17. As the pressure of water on each square 
 inch of surface increases at the rate of about \ lb. ^ 
 for every foot of perpendicular height, if the height 
 from the bottom of the boiler to the top of the pipe 
 be 6 feet, the pressure on the bottom will be 3 lbs. 
 on every square inch of surface ; but if the boiler 
 be two feet high, the pressure on the top — whicli 
 v^^ill be a pressure upwards — will be only 2 lbs. on 
 every square inch of surface, because it will only 
 
 * The exact weight of a perpendicular foot of water, with a 
 base is one square inch, is 3030*24 grains, at the temperature of 
 60° ; which is therefore only '4328 of a pound avoirdupois. A 
 column of water 30 feet high only gives a pressure of 12 68 lbs. 
 instead of 15 lbs. as usually reckoned ; and therefore the real 
 height of a column of water which will give a pressure equal to 
 one atmosphere must be 34j feet. 
 
 c 2 
 
20 
 
 PRESSURE OF WATER. 
 
 have 4 perpendicular feet of water above it. If tlie 
 height of the pipe be increased to 28 feet, and the 
 depth of the boiler be 2 feet, as before, making 30 
 feet together, the pressure will be 15 lbs. on each 
 square inch of the bottom, 14 lbs. on each square 
 inch of the top, and an average pressure of 14^ lbs. 
 on each square inch of the sides of the boiler. 
 Suppose now, a boiler to be 3 feet long, 2 feet 
 wide, and 2 feet deep, with a pipe 28 feet high from 
 the top of the boiler ; when the apparatus is filled 
 with water there will be a pressure on the boiler of 
 66,816 lbs., or very nearly 30 tons. 
 
 18. When a great pressure is used in a hot 
 water apparatus, in the manner here described, it is 
 necessary that the materials of the boiler should be 
 stronger than they otherwise need be ; and more 
 care is also required in making the joints very sound, 
 for attaching the pipes to the boiler, so as to pre- 
 vent any leakage. But when these mechanical 
 difficulties are overcome, the amount of danger aris- 
 ing from a great pressure of water must not be 
 over-rated, for it might otherwise deter some 
 persons from adopting this form of the apparatus, 
 notwithstanding its numerous advantages. 
 
 19. The great danger that arises from the 
 bursting of a steam apparatus, is in consequence of 
 the elastic force of steam, which, at very high 
 temperatures, is immense. But water possesses very 
 little elasticity compared with steam, its expansive 
 
COMPRESSION OF WATER. 
 
 21 
 
 force being almost inappreciable under ordinary 
 circumstances. At the pressure of 15 lbs. per 
 square inch, the water in the boiler last described, 
 which holds about 75 gallons, would be compressed 
 rather less than one cubic inch, or about -3^ part of a 
 pint\ The expansive force of the water in this 
 apparatus, therefore, even supposing it were to burst, 
 would be perfectly harmless ; for it could only ex- 
 pand as much as it had been compressed ; namely, 
 one cubic inch. The effect on a boiler, by the pressure 
 of the water, will be precisely similar to a weight 
 pressing upon it, equal to the estimated pressure of 
 the water ; which is quite different from the sudden 
 and violent force produced by the expansive power 
 of steam. As an apparatus of this kind could never 
 be forced asunder, as in the explosion of a steam 
 boiler, the only result, under the worst circum- 
 stances that could occur, would be a leakage of the 
 water in consequence of the cracking of some part 
 of the boiler. 
 
 20. Neither the principle, nor the practical 
 working of the apparatus, is in the least affected by 
 having any additional number of pipes leading out 
 
 * According to the experiments of Professor Oerstead, the 
 compression of water is '0000461 by a pressure of 15 lbs. per 
 square inch ; and he has found that it proceeds pari passu, as 
 far as 65 atmospheres, which was the limit to which his experi- 
 ments extended. This compression is about equal to reducing a 
 given bulk of water of its volume by a pressure of 20,000 lbs. 
 per square inch. 
 
22 
 
 BRANCH PIPES. 
 
 of, or into, the boiler. The effect is the same whe- 
 ther there are more flow pipes than return pipes, or 
 conversely, more return pipes than flow pipes. If 
 there be two or more flow pipes, whether they lead 
 from the boiler separately, or branch from one main 
 pipe, or whether they lead from opposite sides of 
 the boiler, or all from one side, each range of pipes 
 will act separately and have a velocity of circulation 
 peculiar to itself : and one range of pipes may act 
 efficiently, while another, though attached to the 
 same boiler, may have no circulation whatever 
 through it ; and this effect will not be altered, whe- 
 ther the pipes return into the boiler separately, 
 or all unite into one main pipe. The pressure, 
 supposing the pipes to rise vertically from the 
 boiler, will likewise be precisely the same, however 
 numerous the pipes may be. This circumstance is 
 one of the peculiarities which distinguish fluids 
 from solids. For if the fluid contained in any 
 vessel, be pressed by the fluid in an upright pipe, so 
 as to produce a pressure of 10 lbs. on the square 
 inch ; if a second pipe, capable of exerting a similar 
 pressure with the first, be placed upon the same 
 vessel, the united pressure will still be only 10 lbs. 
 per square inch ; and it would be no more, hoAvever 
 large a number of pipes were added, provided the 
 height were not increased. 
 
 21. One advantage may be attained by causing 
 the water to rise from the boiler by an ascending 
 
 1 
 
VARIATIONS OF LEVEL. 
 
 23 
 
 pipe, as in fig. 5, which cannot be accomplished by 
 any other means ; and it is of considerable import- 
 ance to ascertain its true effect, as it has produced 
 consequences which are not generally attributed to 
 the right cause. 
 
 The force and velocity of motion of the water, 
 being proportional to the height of the ascending 
 and descending pipes, by increasing this height, a 
 facility is afforded for taking the pipes below the 
 horizontal level ; as, for instance, when it is required 
 to pass them under a doorway, or other similar ob- 
 struction, before they finally descend to the bottom 
 of the boiler. Innumerable failures have occurred 
 in attempting to make the water descend and again 
 to ascend in this manner, the success of the experi- 
 ment depending upon the vertical height of the 
 ascending pipe above the boiler. These alterations 
 of the horizontal level, which are frequently very 
 desirable, have, of course, their limits, beyond which 
 they cannot be carried : and it is from not having 
 ascertained what are these limits, and what the 
 cause of the limitation, that such uncertainty has 
 hitherto prevailed with regard to this experiment ; 
 for it frequently succeeds, and almost, or even more 
 more frequently fails, in practice. It will be most 
 convenient, however, to consider this subject after 
 we have ascertained what is the amount of the 
 motive power of the water in this kind of apparatus. 
 
CHAPTER II. 
 
 On the Motive Power of the Water — Velocity of Circulation — 
 On increasing the Motive Power — Circulation of Water below 
 the Boiler — Air Vents — Supply Cisterns — Expansion of 
 Pipes, &c. 
 
 22. It has already been mentioned, that the power 
 which produces circulation of the water, is the 
 unequal pressure on the return pipe, in consequence 
 of the greater specific gravity of the water in the 
 descending pipe, above that which is in the boiler. 
 Whether this force acts on a long length of return 
 pipe, as J/, fig. 2, or only on a very short length, 
 as fig. 3, the result will be precisely similar. 
 
 23. Now, it is evident that, if this unequal pressure 
 is the vis viva, or motive power, which sets in motion 
 the whole quantity of water in the apparatus, it is 
 only necessary, in order to ascertain the exact 
 amount of this force, that we know the specific 
 gravities of the two columns of water; and the 
 difference will, of course, be the effective pressure, 
 or motive power. This can be accurately determined 
 
MOTIVE POWER. 
 
 25 
 
 when the respective temperatures of the water in 
 the boiler, and in the descending pipe, are known. 
 
 24. As this difference of temperature rarely 
 exceeds a very few degrees in ordinary cases, the 
 difference in the weight of the two columns must 
 necessarily be very small. But, probably, the very 
 trifling difference which exists between them, or, in 
 other words, the extreme smallness of the motive 
 power, is very imperfectly comprehended ; and will, 
 perhaps, be regarded with some surprise, when its 
 amount is shown by exact computation. 
 
 25. In order to ascertain, without a long and 
 troublesome calculation, what is the amount of 
 motive power for any particular apparatus, the 
 following Table has been constructed. An apparatus 
 is assumed to be at work, having the temperature 
 in the descending pipe 170°; and the difference of 
 pressure upon the return pipe is calculated, sup- 
 posing the water in the boiler to exceed this tem- 
 perature by from V to 20°. This latter amount 
 exceeds the difference that usually occurs in 
 practice. 
 
 26. By referring to the annexed Table, it will 
 be found that when the difference between the 
 temperature of the ascending and the descending 
 columns, amounts to 8°, the difference in weight is 
 S'\6 grains on each square inch of the section of the 
 return pipe, supposing the height of the boiler 
 (A, fig. 2) to be 12 inches. This height, however, 
 
26 
 
 MOTIVE POWER. 
 
 is only taken as a convenient standard from which 
 to calculate; for, probably, the actual height will 
 seldom be less than about 18 inches, and, in many 
 cases, it will be considerably more. 
 
 Now, suppose, in such a form of apparatus as 
 %. 2, the boiler to be 2 feet high ; the distance from 
 the top of the upper pipe to the centre of the lower 
 pipe to be 18 inches; and the pipe 4 inches 
 diameter ; — if the difference of temperature between 
 the water in the boiler, and in the descending pipe, 
 be 8°, the difference of pressure on the return pipe 
 will be 153 grains^ or about the third part of an 
 ounce weight : and this will be the amount of motive 
 power of the apparatus, whatever be the length of 
 pipe attached to it. If such an apparatus have 100 
 yards of pipe, 4 inches diameter, and the boiler 
 contains, suppose 30 gallons; — there will be 190 
 gallons, or 1900 lbs w^eight of water, kept in con- 
 tinual motion by a force only equal to one-third of 
 an ounce. This calculation of the amount of the 
 motive power, in comparison with the weight moved, 
 will vary under different circumstances ; and in all 
 cases the velocity of the circulation will vary 
 simultaneously with it. 
 
TABLE OF PRESSURES. 
 
 27 
 
 Difference in Weight of Two Columns of Water, each One Foot 
 high, at various Temperatures. 
 
 Difference 
 
 
 
 
 
 
 in 
 
 Temperature 
 
 
 Difference 
 
 in Weight 
 
 
 Difference 
 or a 
 
 of the 
 Two Columns 
 of Water: 
 
 of Two Columns of Water contained 
 in different sized Pipes. 
 
 Column 
 1 foot high. 
 
 in Degrees of 
 
 
 
 
 
 
 
 
 
 
 
 A dill trii iici u o 
 
 
 
 
 
 
 Scale. 
 
 1 in. diam. 
 
 2 in. diam. 
 
 3 in. diam. 
 
 4 in. diam. 
 
 per sqr. in. 
 
 
 grs. weight 
 
 grs. weight 
 
 grs. weight 
 
 grs. weight 
 
 grs. weight 
 
 2^ 
 
 1-5 
 
 6-3 
 
 14.3 
 
 25 4 
 
 2-028 
 
 4° 
 
 3-1 
 
 12-7 
 
 28 8 
 
 51-1 
 
 4 068 
 
 6° 
 
 4-7 
 
 19-1 
 
 433 
 
 76-7 
 
 6-108 
 
 8° 
 
 6-4 
 
 25-6 
 
 .')7-9 
 
 102-5 
 
 8-160 
 
 10° 
 
 8-0 
 
 32-0 
 
 72-3 
 
 128-1 
 
 10-200 
 
 12° 
 
 9-6 
 
 38-5 
 
 87-0 
 
 154-1 
 
 12-264 
 
 14° 
 
 11-2 
 
 45-0 
 
 101-7 
 
 180-0 
 
 14-328 
 
 16° 
 
 12-8 
 
 51-4 
 
 116-3 
 
 205-9 
 
 16-392 
 
 18° 
 
 14-4 
 
 57-9 
 
 131-0 
 
 231-9 
 
 18-456 
 
 20° 
 
 16-1 
 
 64-5 
 
 145-7 
 
 258-0 
 
 20-532 
 
 The above Table has been calculated by the formula given 
 with Table 4, for ascertaining the specific gravity of Water at 
 different temperatures. The assumed temperature is from 170° 
 to 190° 
 
 27. It will be observed in the foregoing table, 
 that the amount of motive power increases with the 
 size of the pipe : for instance, the power is 4 times 
 as great in a pipe of 4 inches diameter, as in one of 
 2 inches. The power, however, bears exactly the 
 same relative proportion to the resistance, or weight 
 of water to be put in motion, in all the sizes alike ; 
 for although the motive power is four times as great 
 in pipes of 4 inches diameter, as in those of 2 inches, 
 the former contains four times as much water as the 
 j 
 
28 
 
 INCREASE OF 
 
 latter : the power and the resistance, therefore, are 
 relatively the same. 
 
 28. As the motive povrer is so small, it is not at 
 all surprising that, by an injudicious arrangement of 
 the different parts of an apparatus, the resulting 
 motion may frequently be impeded, and sometimes 
 even totally destroyed : for the slower the circulation 
 of the water, the more likely is it to be interrupted 
 in its course. There are two ways by which the 
 amount of the motive power may be increased : one, 
 by allowing the water to cool a greater number of 
 degrees between the time of its leaving the boiler, 
 and the period of its return through the descending 
 pipe ; the other, by increasing the vertical height of 
 the ascending and descending columns of water. 
 The effects produced by these two methods are 
 precisely similar ; for by doubling the difference of 
 temperature between the flow pipe and the return 
 pipe, the same increase in power is obtained as by 
 doubling the vertical height ; and tripling the dif- 
 ference in temperature is the same as tripling the 
 vertical height \ This can be ascertained by refer- 
 ring to the preceding Table. Thus, suppose, when 
 the difference of temperature is 8°, and the vertical 
 height 4 feet, that the motive power is 32*6 grains 
 per square inch : if the difference of temperature be 
 increased to 16° while the height remains the same, 
 
 ' This is without reference to friction : the effect will therefore 
 be a little modified by this cause. (See art. 34 & 55.) 
 
MOTIVE POWER. 
 
 29 
 
 or if the height be increased to 8 feet Avhile the 
 temperature remains as at first; — the pressure, in 
 either case, will be 65*2 grains per square inch, or 
 twice the former amount. The same rule applies 
 to other differences, both of height and temperature. 
 
 29. Almost the only two methods of increasing 
 the difference of temperature between the ascending 
 and the descending columns, are, either by increasing 
 the quantity of pipe, so as to allow the water to flow 
 a greater distance before it returns to the boiler; or, 
 by diminishing the diameter of the pipe, so as to 
 expose more surface in proportion to the quantity 
 of water contained in it, and by this means to make 
 it part with more heat in a given time. (See art. 72c) 
 The first of these two methods, however, is neces- 
 sarily limited by the extent of the building that is 
 to be heated, to which the quantity of pipe must be 
 adjusted in order to obtain the required temperature : 
 and as to the second, there are many objections 
 against reducing the size of the pipes, which will be 
 considered presently. The increase of motive power 
 to be obtained by increasing the height of the 
 ascending column of water, is, therefore, what must 
 principally be depended on, when additional power 
 is required to overcome any unusual obstructions. 
 
 30. In all cases the rapidity of circulation is pro- 
 portional to the motive power ; and, in fact, it is the 
 index and the measure of its amount. For if, while 
 
30 
 
 INCREASE OF 
 
 the resistance remains uniform, the motive power be 
 increased in any manner or in any degree, the rate 
 of circulation will increase in a relative proportion. 
 Now the motive power may be augmented, as we 
 have already seen, either by increasing the vertical 
 height of the pipe ; by reducing its diameter ; or by 
 increasing its length. If by any of these means the 
 circulation be doubled in velocity, then, as the water 
 will pass through the same length of pipe in half the 
 time it did before, it will only lose half as much heat 
 as in the former case ; because the rate of cooling is 
 not proportional to the distance through which the 
 water circulates, but to the time of transit. If, then, 
 by sufficiently increasing the vertical height, the 
 difference between the temperature of the flow pipe 
 and the return pipe be diminished one-half, it might 
 be supposed that the motive power of the apparatus 
 would remain the same, and no advantage would 
 appear to be gained by this means. But this is not 
 exactly the case. For although, whether we double 
 the vertical height, or double the horizontal length, 
 we shall, in either case, increase the velocity of 
 motion ; yet, it will require a quadruple increase of 
 vertical height, or a quadruple increase of horizontal 
 length, to obtain double the original rate of circula- 
 tion. (See art. 33.) The increased velocity is 
 therefore indicative of increased power: and, in a 
 hot water apparatus, it is the increased velocity of 
 
MOTIVE POWER. 
 
 31 
 
 circulation, which overcomes any obstructions of a 
 greater amount than ordinary. 
 
 31. The velocity with which the water circulates 
 in this kind of apparatus, although continually 
 subject to variation, can nevertheless be calculated 
 theoretically, when certain data are agreed upon, or 
 are ascertained to exist. 
 
 32. When the two legs of an inverted syphon, a 
 fig. 6, are filled with liquids of unequal density, if 
 the stop cock, 0, be turned, so as to yig.g. 
 open the communication between them, 1 
 
 the lighter liquid will move upwards ^ 
 with a force proportional to the dif- 
 ference of weight of the two columns, 
 provided the bulk of the two liquids be 2 
 equal. If one leg contains oil, and the other contains 
 'water, the relative weights will be about as 9 to 10 ; 
 therefore it will require 10 inches vertical height of 
 oil, to balance 9 inches of water ; and no motion 
 will in that case take place. But when equal bulks 
 of the two fluids are used, the velocity of motion 
 with which the lighter fluid is forced upwards, is 
 equal to the velocity which a solid body would 
 acquire in falling, by its own gravity, through a space 
 equal to the additional height which the lighter body 
 would occupy in the syphon, supposing a similar 
 weight of each fluid had been used. This velocity is 
 easily calculated : — a gravitating body falls 16 feet 
 in the first second of time of its descent ; 04 feet in 
 
32 
 
 VELOCITY OF 
 
 two seconds, and so on ; the velocity increasing as 
 the square of the time: therefore, the relative 
 velocities are, as the square roots of the heights. 
 Now, in the case of the syphon, which we have 
 supposed to contain a column of water and a column 
 of oil, each 9 inches in height ; as the oil ought to 
 be 10 inches high to balance the 9 inches of water, 
 the oil in the one leg will be forced upwards with a 
 velocity equal to that which the water (or any other 
 body) would acquire by falling through one inch of 
 space ; and this velocity, we shall find, is equal to 
 138 feet -per minute \ 
 
 33. To estimate the velocity of the motion of the 
 water, in a hot-water apparatus, the same rule 
 will apply. If the average temperature be 170°, 
 the difference between the temperature of the 
 
 ^ The velocity will be as the square root of 16 feet fer second, 
 to the square root of the additional height which an equal weight 
 of the lighter liquid would occupy, reduced to the decimal of a 
 foot. And as the acquired velocity of a body is twice as much 
 as the distance it passes through, in arriving at any given velocity 
 by accelerated motion ; or, in other words, as a body which falls 
 through 16 feet of space, in one second, will proceed at the rate 
 of 32 feet per second afterwards, without receiving any additional 
 impulse ; so the velocity found by this rule will be only half the 
 real velocity ; and the number thus obtained must be multiplied 
 by 2. The velocity will, therefore, be found, by multiplying the 
 square root of the difference between the height of the two 
 columns, by the square root of 16 ; and then, multiplying that 
 product by 2, will give the real velocity per second. 
 
 The discharge through a syphon, employed to empty casks and 
 other vessels, can also be calculated by this rule : the velocity of 
 motion will be equal to the difference in length of the two legs. 
 
CIRCULATION, 
 
 33 
 
 ascending and the descending columns 8°, and the 
 height 10 feet ; when similar weights of water 
 are placed in each column, the hottest will stand 
 •331 of an inch higher than the other'; and this will 
 give a velocity equal to 79*2 feet per minute. If 
 the height be 5 feet, the difference of temperature 
 remaining as before, the velocity will be only 55*2 
 feet per minute : but if the difference of temperature 
 in this last example had been double the amount 
 stated, — that is, had the difference of temperature 
 been 1 6°, and the vertical height of the pipe 5 feet, — 
 then the velocity of motion would have been 79*2 
 feet per minute, the same as in the first example, 
 where the vertical height was 10 feet, and the 
 difference of temperature 8°. This, therefore, proves, 
 in corroboration of what has been already stated (art. 
 30), that reducing the temperature of the water, either 
 by using smaller pipes, or by increasing the length 
 through which it flows, has the same effect on the 
 circulation as increasing the vertical height. The 
 velocity for 3 feet of vertical height by the same 
 rule will be 43*2 feet per minute ; for 2 feet of ver- 
 tical height, it will be 36 feet per 7ninute ; and for 
 18 inches of vertical height it will be 30*7 feet^^^- 
 7mnute, if the difference of temperature between the 
 two columns be in each case 8°, the same as in the 
 former examples. It must here be observed, how- 
 
 ^ The exiDansion of water by beat, will be found by Table IV. 
 
 D 
 
34 
 
 VELOCITY OF 
 
 ever, that although it appears by these calculations, 
 that increasing the vertical height of the pipe four- 
 fold, will produce a double velocity of circulation, as 
 the water will then pass through the pipe in half 
 the time, the difference between the temperature of 
 the flow pipe and the return pipe will be lessened 
 one half, and the velocity will at last become a 
 mean rate : so that the mere quadruple increase 
 of vertical height, without the horizontal length be 
 at the same time increased, will only produce a rate 
 of circulation about one and a half times the original 
 velocity. 
 
 34. Such is the result of theory : but, although 
 this is true in itself, we shall, in practice, find but 
 few cases that in any way agree with these results, 
 in consequence of other causes modifying the effects. 
 In an apparatus in which the length of pipe is not 
 very considerable, where the pipes are of large dia- 
 meter, and the angles few, a deduction, according 
 to the circumstances, of from 10 to 20 per cent, from 
 the theoretical amount, will represent, with tolerable 
 accuracy, the true velocity. But in more complex 
 apparatus, no approximation can be obtained by 
 this means : for the velocitv of circulation in such 
 cases becomes so much reduced by friction, that it 
 will sometimes require from 50 to 90 per cent, and 
 upwards, to be deducted from the calculated velo- 
 city, in order to obtain the true rate of circulation. 
 The calculation of the friction of water passing 
 
CIRCULATION. 
 
 35 
 
 through pipes, is alike complicated and unsatisfac- 
 tory : though the question has been investigated by 
 some of the most able philosophers and mathema- 
 ticians, a simple and correct formula on this subject 
 is still a desideratum ; and in the present state of 
 knowledge of the subject, it would be almost im- 
 possible to determine what would be the resulting 
 velocity of circulation, in a hot water apparatus of 
 complicated construction ^ 
 
 35. In addition to these causes which impede the 
 circulation, there is another that is still more im- 
 portant. The vertical angles in the pipe, or those 
 angles which carry the pipe below the horizontal 
 level, increase the resistance to a very considerable 
 extent ; for they oppose not merely a passive resist- 
 
 * M. Prony and M. Bossut calculate the velocity to be in- 
 versely as the square root of the length of pipe, and also, directly 
 as the square of the velocity. The formula of Prony for the 
 
 friction of straight pipes is v = 26*79 where v represents 
 
 the mean velocity ; d the diameter of the pipe ; z the altitude of 
 the head of water; l the length of the pipe in metres. The 
 various formulae of Bossut, Girard, Eytelwein, and others, 
 are too complicated to be introduced here : (see Prony, On the 
 Motion of Fluids, Memoires des Savans Etrangers, &c., 1835 : — 
 Eytelwein's Hydraulics by Nicholson : — Brit. Sci. Reports, vol. 
 II., &c.) Mr. G. Rennie (Phil. Trans. 1831), has given the result 
 of some experiments on this subject. He found that the velocity 
 in a ^ inch pipe, was reduced nearly three-fourths (that is, from 
 3*7 to 1), by increasing its length from 1 foot to 30 feet; that 3 
 semicircular bends reduced the velocity -jg in a short pipe, and 
 14 such bends reduced it of its velocity : while 24 right an- 
 gled bends reduced the velocity nearly two-thirds. The pipe in 
 each case was only ~ inch diameter. 
 
 D 2 
 
36 
 
 MOLECTTLATl MOTION 
 
 ance by friction, but they engender a force of their 
 own, tending in an opposite direction to that of the 
 prime moving power. 
 
 36. The motion of the heated particles of water 
 is very different in passing through an ascending- 
 pipe, compared with that which takes place in a 
 descending pipe. The heated particles rise upwards 
 through an ascending pipe with great rapidity, and 
 when the space occupied by the displaced particles 
 is supplied by water from below, the motion becomes 
 general, in one direction, being most rapid in the 
 centre, and gradually decreasing towards the circum- 
 ference, where, on account of the friction, it becomes 
 comparatively slow. But in a descending pipe, the 
 circumstances are very different, the motion being 
 much more like that of a solid body. For as the 
 heated particles are unable to force their way down- 
 wards through those which are colder and heavier 
 than themselves, the only motion arises from the 
 cold water flowing out at the bottom, its place being- 
 then supplied at the top by that which is warmer ; 
 the whole apparently moving together, instead of 
 the molecular action, which has been described as 
 the proper motion in an ascending pipe. 
 
 37. In an apparatus 
 constructed as fig. 7, the 
 motion through the boiler 
 and pipe a, b, and through 
 the descending pipe c, d 
 
IN WATER. 
 
 37 
 
 takes ])lace according to the two methods here 
 described. But it is evident that, on motion com- 
 mencing in the return pipe j/, in consequence of 
 the greater pressure of c, d, than of a, b, the water 
 from A will be forced towards at the same time 
 that the water in e^f^ h, flows towards c. But 
 when a very small quantity of hot water has passed 
 from the pipe and boiler a, b, into the pipe e,f^ the 
 column of water g, Ji, will be heavier than the co- 
 lumn e,f, and therefore there will be a tendency for 
 motion to take place along the upper pipe, towards 
 the boiler instead of from it. This force, whatever 
 be its amount, must be in opposition to that which 
 occurs in the lower or return pipe, in consequence 
 of the pressure of c, d, being greater than a, b ; and, 
 unless, therefore, the force of motion in the descend- 
 ing pipe c, D, be sufficient to overcome this tendency 
 to a retrograde motion, and leave a residual force 
 sufficient to produce direct motion, no circulation of 
 the water can take place. 
 
 38. An extremely feeble power will produce cir- 
 culation of the water, in an apparatus where there 
 are no unusual obstructions; but it is a necessary 
 result of tlie motive power being so very small, 
 that it is easily neutralized. I have known so 
 trifling a circumstance as a thin shaving planed off 
 a piece of wood, by accidentally getting into a pipe, 
 effectually prevent circulation in an apparatus other- 
 wise perfect in all its parts. 
 
38 
 
 OBSTRUCTIONS IN 
 
 39. It is not sufficient, then, when such an ob- 
 struction as the vertical declination from the hori- 
 zontal level, shown by the last figure, has to be 
 surmounted, merely to make the direct force of 
 motion sufficient to overcome the antagonist force, 
 and to leave the smallest possible residual amount 
 for the purpose of causing circulation ; because an 
 amount which would be sufficient for this purpose, 
 as an undivided force, would not be found sufficient 
 as a residual force. 
 
 40. In estimating the additional height, which it is 
 necessary to give to the ascending column, in order 
 to overcome such an obstruction as shown in fig. 7, 
 it will be necessary to take into account what is 
 the length and diameter of the pipe through which 
 the water passes, between the time of its egress 
 and regress ; for on this depends the difference of 
 temperature between the ascending and descending 
 columns, which, we have seen, materially affects the 
 amount of the motive power of the apparatus. If 
 the length of pipe be considerable, a smaller increase 
 of the vertical height of the ascending pipe will 
 suffice ; but if the length of pipe be short, a greater 
 height must be allowed. The temperature to which 
 the air surrounding the pipes is to be raised, will 
 also modify the result ; for on this will depend the 
 quantity of heat given out by the pipes per minute^ 
 which likewise affects the temperature of the de- 
 scending pipe. (Art. 96.) 
 
THE CIRCULATION. 
 
 39 
 
 4 1 . Under such a great diversity of circumstances, 
 it would be difficult to form a rule for estimating 
 what ought to be the height of the ascending pipe 
 in such cases ; because, not only are these circum- 
 stances different in each apparatus, but they like- 
 wise differ, in some respects, in the same apparatus, 
 in the different stages of its working. The diffi- 
 culty is also increased by not being able to fix on 
 an absolute minimum measurement, which is suffi- 
 cient, under all circumstances, to cause a circulation 
 of the water in the common form of the apparatus. 
 There have been instances where apparatus have 
 succeeded, though constructed on the very worst 
 principles, in consequence of various circumstances 
 having favoured the result. Thus in an apparatus, 
 constructed as fig. 8, Fig. 8. 
 
 apart, the water circulated with perfect freedom; 
 but in this case, not only was the pipe of consider- 
 
 size of the pipe was only two inches diameter, so 
 that the water cooled twice as fast as it would have 
 done had pipes of four inches diameter been used (Art. 
 72). It is, however, quite certain that such a distance 
 between the pipes, at their insertion into the boiler, 
 as that which has just been described, is insufficient, 
 under ordinary circumstances, to give a steady and 
 good circulation. But when the two pipes are about 
 
 where the pipes were 
 not more than 3 inches 
 
 able length, and without angles, or turns, but the 
 
40 
 
 OBSTRUCTIONS IN 
 
 1 2 inches apart, at the place of their insertion into 
 the boiler (d; /I fig. 3), which is 16 inches from centre 
 to centre when the diameter of the pipe is 4 inches, 
 it will be sufficient to produce a good circulation for 
 almost any ordinary length of pipe, when it is not 
 required to dip below the horizontal level. If this 
 be considered as the minimum height which, under 
 ordinary circumstances, will obtain a good circula- 
 tion when the pipes are not required to dip below 
 the horizontal level, then an average height can be 
 estimated for enabling any vertical declination of 
 the pipes to be made. 
 
 42. In such cases the height of the ascending 
 pipe should generally be just so much greater than 
 the above dimensions, as the depth which the circu- 
 lating pipe is required to dip below the horizontal 
 level ; bearing in mind the circumstances mentioned, 
 art. 40, which modify the general results'. Thus 
 suppose the depth of the dip, shown by the dotted 
 line a, d, fig. 9, to be 24 inches ; then the distance 
 9/, z, ought to be 40 inches, if the pipes be 4 inches 
 diameter ; that is 36 inches from centre to centre, 
 
 ^ So greatly, in fact, do these circumstances affect the general 
 result, that it is very possible, if the pipes be of small diameter, 
 and of great length, to make them descend below the bottom of 
 the boiler to a considerable depth. It is therefore evident that 
 the dimensions which are here given for the height of the ascend- 
 ing pipe relatively to the dip, must not be taken as an absolute 
 minimum, but simply as a general rule which will succeed in all 
 cases. Sec Art. 44 and 45. 
 
THE CIRCULATION. 
 
 41 
 
 Fig. 9. 
 
 or 40 inches from the top of the pipe y to the 
 bottom of the pipe z : and with these dimensions, 
 as good a circulation will be obtained, as when the 
 distance between the top and bottom pipes is 1 6 
 inches from centre to centre, in the common form 
 of the apparatus. It will be observed that, by this 
 arrangement, the distance c, c?, from the under side 
 of the flow pipe to the upper side of the return 
 pipe, is just 12 inches, which is the same height 
 that was stated to be necessary to insure a good 
 circulation, on the ordinary plan, without a vertical 
 dip. The reason why this height is sufficient in 
 the present case, notwithstanding the increased 
 friction of the angles, is because there must always 
 be a greater difference between the temperature of 
 e and than between either g and /^, or between 
 i and or even more than between both these 
 together; therefore the tendency to dived motion 
 is greater than towards retrograde motion, in pro- 
 portion to this difference, and is sufficient to over- 
 come the increased friction caused by the vertical 
 declination : while the additional height of 12 inches 
 
42 
 
 OBSTRUCTIONS IN 
 
 beyond the height of the dip, possessed by the 
 descending pipe is sufficient to produce circulation 
 of the water. If g and /^, and also i and were 
 very wide apart, say 40 or 50 feet, instead of 
 being, as usual, only about 3 or 4 feet, the balance 
 of effect, though still in favour of direct motion, 
 would not be so great as in the last supposed case; 
 because there would be a greater difference in tem- 
 perature between g and A, (that is, li would be 
 heavier than ^ in a greater degree), which would 
 give a greater tendency to retrograde motion. In 
 extreme cases, therefore, it will be advisable to 
 make the ascending pipe somewhat higher in pro- 
 portion to the dip than is here stated, particularly 
 when there are several such alterations required in 
 the level of the pipes ; and, in all cases, as has been 
 before observed, the higher the ascending pipe is 
 made, the more rapid will be the circulation. 
 
 43. The difficulty of producing circulation of the 
 water in this form of the apparatus, is always greater 
 on every occasion of first lighting the fire ; because 
 the temperature of the two pipes, which form the 
 ascent and descent of the dip, will always be more 
 nearly equal when the whole of the apparatus has 
 become hot. If, therefore, a small suction-pump be 
 attached to the upper pipe at fig. 7, and, after the 
 water in the boiler has become heated, a few strokes 
 of the pump be made, so as to draw the hot water 
 from the boiler through the wpfer pipe, circulation 
 
 1 
 
THE CIRCULATION. 
 
 43 
 
 may be produced in an apparatus which, without 
 this assistance, would never act at all. For it is 
 evident that when the ascending and descending 
 pipes of the dip are nearly close to one another, if 
 circulation be once obtained, the water will lose so 
 very little of its heat during its transit through this 
 short distance, that the tendency to retrograde 
 motion will be but very small. A pump is, however, 
 by no means a desirable addition to the apparatus, 
 when it can possibly be avoided ; for not only will it 
 be more liable to derangement, but greater attention 
 will be necessary in setting it to work : for the water 
 must first be warmed in the boiler, and then the 
 circulation must be produced by using the pump. 
 1 1 will, therefore, only be desirable to adopt it, when 
 a sufficient height for the ascending pipe of the 
 boiler cannot be obtained, to produce circulation 
 without this assistance. 
 
 What has here been observed with respect to the 
 height of the ascending pipe, relatively to the vertical 
 declination, or dip, below the level of the horizontal 
 pipe, applies to all the usual forms which are given 
 to the apparatus. But there are peculiar arrange- 
 ments which may be adopted, that will allow the 
 dip of the circulating pipe to be much greater in 
 proportion to the vertical height above the boiler, 
 than has here been stated ; for, in some cases, the 
 dip-pipes may even pass below the bottom of the 
 boiler to a considerable depth, without destroying 
 
44 
 
 CIRCULATION OF WATER 
 
 Fig. 10. 
 
 the circulation. Tiiis }>laii is not very dissimilar to 
 that adopted by the Marquis de Chabannes, about 
 twenty years ago. 
 
 44. In such an arrangement of pipes as fig. 10, 
 the circulation depends entirely upon the quantity 
 of heat given off by 
 the coil c ; for. it is 
 evident that, when 
 the boiler B and pipe 
 a are heated, the di- 
 rect motion will arise 
 in consequence of 
 the greater weight of 
 the water in the coilc 
 and pipe d, above that 
 which is in the boiler and pipe b, a. But as the 
 water in the pipe e, below the dotted line, will be 
 lighter than that in the pipe f, the tendency in that 
 part of the apparatus will be towards a retrograde 
 motion. The result of these two forces will be, that 
 if the water in the whole length of pipe w, a% is 
 heavier than that of the whole length j/, z, in a suffi- 
 cient degree to overcome the friction, circulation of 
 the water will take place; and the velocity of motion 
 will depend upon the amount of this difference in 
 weight. 
 
 45. Another form, though somewhat more com- 
 plicated, may be given to this arrangement of the 
 apparatus. In fig. 1 1 , B represents the boiler ; and 
 
BELOW THE BOILER. 
 
 45 
 
 tlie effective or direct motion is, in this case, caused 
 by the water in the ^ig. ii . 
 
 coil and pipe c, d, 
 being so much hea- 
 vier than that in 
 the boiler and pipe 
 B, a, that it over- 
 comes the retro- 
 grade motion which 
 is produced by all 
 the other parts of 
 
 the apparatus. Thus the water in A, being Jieamer 
 than that in z, k ; and that in f, (below the dotted 
 line) being lighter than that in /, 7n, has, in both 
 cases, a tendency to retrogression ; and this will be 
 more considerable in proportion as the pipes z, k, 
 and g, h, &c., are more distant from each other. 
 The motive power, therefore, entirely depends upon 
 the quantity of heat given off by the coil ; for the 
 water must be cooled down many degrees, in order 
 to give it a sufficient preponderance over the water 
 in B, a, to cause a circulation. 
 
 46. If the coil, in the tw^o last figures, be placed 
 in any position lowTr doM^n than it is here shown, 
 the effect will be proportionally less ; and if placed 
 below the dotted lines, it would be scarcely possible 
 to obtain any circulation at all. Nor would there 
 be any circulation if the coil M ere omitted, because 
 the mere descent of the water through a straight 
 
4(3 
 
 ACCUMULATION OF 
 
 pipe, would not cool it sufficiently to give the neces- 
 sary preponderance to the descending pipe, unless 
 some other contrivance, for the purpose of cooling 
 the water an equal extent, were adopted. 
 
 47. Many other arrangements of the apparatus 
 answering the same purpose as these last two figures, 
 might be contrived ; but it may be observed, that 
 these des(^riptions have been introduced principally 
 to show that the notion that it is impossible to make 
 water descend and circulate below the boiler, is 
 erroneous. It, however, requires great judgment 
 in adopting any such form of the apparatus as this, 
 for many concurring circumstances are essential for 
 its complete success. 
 
 48. In a complicated arrangement of the appa- 
 ratus, it is sometimes so very difficult to detect the 
 various causes of interference, and the impediments 
 which arise are often apparently so insignificant in 
 their extent, that even when ascertained, they are 
 frequently neglected. Those, however, who bear in 
 mind how small is the amount of motive power in 
 any apparatus of this description, will not consider 
 as unimportant, any impediment, however small, 
 which they may detect ; but in the more complicated 
 forms of the apparatus, so many causes become opera- 
 tive, that the reason of failure may sometimes elude 
 the detection of even an experienced practitioner. 
 
 49. The necessity of making provision for the 
 escape of the air from the pipes, has already been 
 
AIR IN PIPES, 
 
 47 
 
 mentioned. It may be observed, that in such forms 
 of the apparatus as described in the last three figures, 
 the difficulty of its expulsion is much increased, as 
 there are several points where it will collect and 
 stop the circulation, unless proper means be taken 
 to prevent this result. In the apparatus fig. 9, the 
 air will collect at three points /, m, and n ; and the 
 nature of the outlets provided for its escape, will 
 depend, in some measure, upon the plan adopted 
 for supplying the apparatus with w^ater. It fre- 
 quently requires the greatest care and the closest 
 attention, to discover where the air is likely to lodge, 
 as the most trifling alteration in the position of the 
 pipes will entirely alter the arrangements with 
 respect to the air vents. Want of attention to this 
 has been the cause of many failures ; and the dis- 
 covery of the places where the air will accumulate, 
 is, occasionally, a matter of some difficulty. For 
 although it be true, in a general sense, that the air 
 will rise to the highest part of the apparatus, it will 
 frequently be prevented getting to those parts by 
 alterations in the level of the pipes, and by other 
 causes. This is the case at fig. 9, where, it will 
 be seen, the air which accumulates in that part of 
 the apparatus is prevented from escaping to a higher 
 level, by the vertical angle at f, on the one side, 
 and z, on the other. In the apparatus, fig. 11, the 
 air will accumulate at y, and at and must be car- 
 ried olf by proper outlets. 
 
48 
 
 EXPANSION OF WATER. 
 
 50. When a boiler lias an open top, or merely a 
 loose cover laid on it, no particular care is necessary 
 respecting the supply of water. It can generally be 
 poured in at the boiler, taking care not to fill it 
 quite full, so as to allow for the expansion of the 
 water when heated, as otherwise it will overflow. 
 But when (as in figures 7, 9, 10, and 1 1,) the boiler 
 is close at the top, it is usual to place a supply 
 cistern on a level with, or above the highest part of 
 the apparatus, so as to keep it always full of water. 
 But as water expands about -^-^ part of its bulk, 
 when it is heated from 40° (the point of its greatest 
 condensation,) to 212°; it is indispensably necessary 
 to provide for a part of the water returning back to 
 the supply cistern, when this expansion takes place. 
 The cistern, however, needs not contain so much 
 water as part of the whole contents of the appa- 
 ratus ; for it is found, in practice, that a much less 
 quantity than this returns back into the cistern on 
 the apparatus being heated. This arises from the 
 fact of the water not reaching to so high a tempera- 
 ture as 212°, and also in consequence of its being 
 generally at a higher temperature than 40°, before it 
 is heated, and by both these causes, the expansion is 
 considerably lessened ; for if the water be raised 
 from 50° to 180°, the expansion will only be about 
 
 part of its bulk, and the expansion of the iron 
 itself, by giving an increased capacity to the appa- 
 ratus, will also tend still farther to diminish the 
 quantity of water returned back into the cistern. 
 
SUPPLY CISTERNS. 
 
 49 
 
 Fig. 12. 
 
 51. The usual plan for a supply cistern is shown 
 in fig. 12. The cistern is placed in some convenient 
 situation, and then attached, by a small pipe, to 
 any part of the apparatus, — usually, to the lower 
 pipe, as it is then less 
 likely to allow of the 
 escape of vapour, than 
 if it were fastened to 
 the top of the boiler. X^..^--^^^ 
 But a still better plan is to bend the pipe, attached 
 to the cistern, into the form shown by which is 
 a preventive to the escape of any heat or vapour at 
 that part, as the legs of the inverted syphon x 
 generally remain quite cold. 
 
 52. One very important part of the subject of 
 expansion, is the necessity which exists for allowing 
 sufficient room for the elongation of the pipes when 
 they become hot. Want of attention to this has 
 caused several accidents ; for the expansive power of 
 iron, when heated, is so great, that scarcely anything 
 can withstand it. The linear expansion of cast iron, 
 by raising its temperature from 32° to 212°, is 
 •0011111, or about -^-^ part of its length, which is 
 nearly equal to \\ inches in 100 feet. Therefore it 
 is necessary to leave the pipes unconfined, so that 
 they shall have free motion lengthways, to this 
 extent at least ; and instead of confining them, as 
 sometimes has been done, facilities should be pro- 
 vided for their free expansion, by laying small rollers 
 
 E 
 
50 
 
 EXPANSION OF PIPES. 
 
 under them at various points : for as the contraction 
 on cooling is always equal to the expansion on heat- 
 ing, unless they can readily return to their original 
 position when they become cool, the joints are very 
 likely to get loose, and to become leaky. 
 
 « 
 
CHAPTER III. 
 
 On the Resistance by Friction — Relative Sizes of Main Pipes 
 and Branch Pipes — Size of Connecting Pipes, Cocks, &c. 
 
 53. When treating, in the preceding chapter, on 
 the velocity of the circulation of the water, it was 
 observed that the theoretical velocity is always 
 reduced by friction. Although the calculations of 
 the friction of water, in passing through pipes, is in- 
 tricate ^ the 7'elatwe friction for different sizes of 
 pipes is easily ascertained ; and this appears to be all 
 that is necessary to be acquainted with, for the pur- 
 pose of the present inquiry. 
 
 54. The friction occasioned by water passing 
 through small pipes, is very much greater than in 
 those which are larger. This arises from two causes : 
 the increased surface with which a given quantity of 
 water comes into contact, by passing through a small 
 pipe ; and the greater velocity with which the water 
 
 ^ See Art. 34. 
 E 2 
 
52 
 
 FRICTION OF PIPES. 
 
 circulates, in consequence of losing more heat per 
 minuted 
 
 55. The relative friction for different sizes of pipe, 
 when the velocity with which the water passes is 
 the same in all, may be seen in the following Table : 
 
 Diameter of Pipes ^. 1. 2. 3. 4. inches. 
 Friction 8. 4. 2. VS. 1. 
 
 Taking the friction, in pipes of 4 inches diameter, as 
 unity, — that of a pipe 2 inches diameter is twice 
 as much, and a 1-inch pipe four times as much as 
 the pipe of 4 inches; the friction being as the 
 surface directly^ and the whole quantity of water 
 inversely.^ 
 
 56. The friction which arises from increased velo- 
 city, is nearly as the square of the velocity ; but this 
 calculation is unnecessary to enter into here, because 
 the velocitv of circulation of the water, in a hot- 
 water apparatus, is constantly subject to fluctuation : 
 for as the friction increases with the velocity of cir- 
 culation, so the velocity is checked by the increased 
 friction; and it finally assumes a mean rate, propor- 
 tioned to the friction on the one hand, and the 
 theoretical velocity on the other, calculated ac- 
 
 ^ See Chap. IV, art. 72. This latter remark of course only 
 applies to water circulating in a hot-water apparatus : the former 
 applies to all cases of hydraulics. 
 
 ^ Nicholson's Journal, Vol. iii., page 31. 
 
MAIN PIPES. 
 
 53 
 
 cording to the rule (art. 33,) in the preceding 
 chapter. 
 
 57. Closely connected with the subject of friction, 
 is the question of the proper size for leading, or 
 main pipes. It has been supposed by many, that 
 where two or more circulating pipes are attached to 
 one main pipe, the area, or section, of the main pipe, 
 ought to be equal to the sum of the areas of all the 
 branch pipes. This has led to the most incon- 
 venient arrangements having been resorted to in 
 particular cases. In some instances, pipes of 9 inches 
 diameter have been used for the main pipes, where 
 those of 4 inches would have answered the purpose 
 infinitely better. 
 
 58. It has been already explained (art. 36) why 
 the motion of water is more rapid in an upright, 
 than in a horizontal pipe. If four branch pipes are 
 supplied by one upright main pipe, this latter needs 
 be very little, if any, larger than the circulating pipe : 
 but if only two, or even three, branches are to be 
 supplied by one main pipe, it will be quite unne- 
 cessary that the main pipe should be any larger than 
 the branches, unless the length of the horizontal 
 pipe be unusually great. If the branches exceed 
 this number, it may be desirable to increase the 
 diameter of the main pipe, in a moderate degree : but 
 the motion of the water through it, however, will 
 be just so much the more rapid, in proportion as 
 there are more branches for it to discharge the water 
 
54 
 
 MAIN PIPES. 
 
 into : for it is evident, that if the outlet from the 
 boiler be by a pipe 4 inches diameter, the flow of 
 water will be more impeded, than if a pipe of 6 inches 
 diameter were used; and the water will be specifically 
 lighter in the boiler than in the descending pipe, in 
 a greater degree in the former case, than in the 
 latter ; and this will consequently cause a more 
 rapid circulation through the apparatus : but though 
 the friction of the water will be greater in the 
 ascending pipe by this arrangement, yet it will not 
 be of much importance, except when very small 
 pipes are used. 
 
 59. Another advantage will arise from this ar- 
 rangement, in consequence of a small pipe, under 
 these circumstances, losing less of its heat than a 
 large one. For, suppose four branch pipes, 4 inches 
 diameter, are to be supplied by one main pipe ; one 
 pipe of 8 inches diameter would have the same 
 sectional area as the four pipes of 4 inches diameter : 
 but if instead of being 8 inches diameter, the main 
 pipe be made only 4 inches diameter, then the 
 water must travel four times as fast through this 
 pipe, as it would do through the one of 8 inches 
 diameter, in order to supply the same quantity of 
 heat to the branch pipes. This it will do very 
 nearly ; and it may easily be deduced, that, under 
 these circumstances, the water will only lose one 
 half as much heat by passing through the small pipe, 
 as it would in passing through the larger one. 
 1 
 
CONNECTING PIPES. 
 
 55 
 
 60. On the same principle, it will frequently be 
 found exceedingly convenient, when two rooms or 
 buildings, somewhat distant from each other, are 
 required to be warmed by one boiler, to make the 
 connecting pipe between them much smaller than 
 the pipe used for radiating the heat to warm the 
 buildings. For, on the principle already mentioned, 
 there will be a saving, as well in heat, as in the cost 
 of the apparatus, by reducing the size of the pipe 
 in that part which is not required to give off heat, 
 but which is merely used to connect different parts 
 together \ 
 
 61. The same rule may likewise be followed, 
 where stop-cocks are required occasionally to shut 
 off the communicatioa between different parts of 
 an apparatus, so as only to warm one particular 
 room or part of a building. The cocks used for this 
 purpose, need not be near so large as the bore of the 
 pipes ; for exactly in proportion as they are smaller, so 
 
 ^ As all alterations in the size of the pipe, either by enlarging 
 or contracting its diameter, materially alters the velocity of 
 circulation of the water, care should be taken that these altera- 
 tions be not made without some decided advantage appears 
 to be attainable by so doing. Venturi found by experiment, 
 that enlargements in a pipe reduced the velocity of discharge 
 as follows : — When a given quantity of water was discharged 
 through 
 
 A straight pipe in 109'' 
 
 A pipe with 1 enlargement, required .... 147'' 
 
 3 
 5 
 
 192'' 
 240" 
 
56 
 
 STOP-COCKS. 
 
 much the more rapidly will the water pass through 
 the obstruction \ Some judgment, however, must 
 be exercised in all such cases : for both with con- 
 necting pipes and cocks, if the size be very dispro- 
 portionate, the free circulation of the water will of 
 course be impeded. In most cases, a cock of 2 
 inches diameter, will be sufficiently large to use 
 with pipes of 4 inches diameter; and a cock of 
 IJ inch diameter, with pipes of 3 inches diameter: 
 but for very small pipes, the relative proportions 
 should perhaps be more nearly equal, on account 
 of the increased friction. 
 
 62. Though some of these propositions may ap- 
 pear to be at variance with the laws of hydraulics, 
 they will nevertheless be found correct; because 
 several of the effects are to be referred either en- 
 tirely to hydrostatic laws, or to a complicated result 
 of hydrodynamics ; and therefore they are not to be 
 judged of by simple hydraulic principles. In fact, 
 the correctness of the theories advanced in this 
 treatise, which are of a practical character, and 
 admit of verification, have been tested, more or less 
 extensively, by actual experiment, and do not, 
 therefore, rest merely on hypothetical reasoning. 
 
 ^ As this may at first appear doubtful, it should be borne 
 in mind, that this kind of obstruction to the circulation, will 
 cause a greater di{Ference between the temperature of the flow 
 pipe and the return pipe ; and, when this occurs, the velocity of 
 the circulation must always be increased. 
 
CHAPTER IV. 
 
 Permanence of Temperature— Rates of Cooling, for different 
 sized Bodies — Relative Size of Pipes and Boilers — Objections 
 against Small Boilers — Proper Size of Boilers, for any given 
 Length of Pipe. 
 
 63. One of the greatest advantages which the plan 
 of heating by the circulation of hot water possesses 
 over all other inventions for distributing artificial 
 heat, is, that a greater permanence of temperature 
 can be obtained by it, than by any other method. 
 The difference between an apparatus heated by hot 
 water, and one where steam is made the medium 
 of communicating heat, is no less remarkable in 
 this particular, than in its superior economy of fuel. 
 
 64. It seldom happens that the pipes of a hot- 
 water apparatus can be raised to so high a tempera- 
 ture as 212° ; and in fact, it is not desirable to do so ; 
 because steam would then be formed, and would 
 escape from the air vent, or safety pipe, without 
 affording any useful heat. Steam pipes, on the 
 
58 
 
 COMPARISON OF HEAT 
 
 contrary, must always be at 212° at the least, be- 
 cause, at a lower temperature, the steam will con- 
 dense. A given length of steam pipe, will therefore 
 afford more heat than the same quantity of hot- 
 water pipe : but, if we consider the relative perma- 
 nence of temperature of the two methods, we shall 
 find a very remarkable difference in favour of pipes 
 heated with hot water. 
 
 65' The weight of steam at the temperature of 
 212°, compared with the weight of water at 212°, 
 is about, as 1 to 1694 ; so that a pipe which is filled 
 with water at 212°, contains 1694 times as much 
 matter as one of equal size filled with steam. If 
 the source of heat be withdrawn from the steam 
 pipes, the temperature will soon fall below 212°, 
 and the steam immediately in contact with the 
 pipes will condense : but in condensing, the steam 
 parts with its late^it heat ; and this heat in passing 
 from the latent to the sensible state, will again 
 raise the temperature of the pipes. But as soon as 
 they are a second time cooled down below 212°, a 
 further portion of steam will condense, and a fur- 
 ther quantity of latent heat will pass into the state 
 of heat of temperature ^ ; and so on until the whole 
 quantity of latent heat has been abstracted, and the 
 
 ^ The heat of temperature is that which is appreciable by the 
 thermometer; and the term is used in contra-distinction to latent 
 heat, which is not capable of being measured in a direct manner 
 by any instrument whatever. 
 
IN WATER AND STEAM. 
 
 59 
 
 whole of the steam condensed, in which state it will 
 possess just as much heating power, as a similar 
 bulk of water at the like temperature ; that is, the 
 same as a quantity of water occupying YrtT P^^^ 
 the space which the steam originally did. 
 
 66. The specific heat of uncondensed steam com- 
 pared with water, is, for equal weights, as '8470 
 to 1 : but the latent heat^ of steam being estimated 
 at 1000°, we shall find the relative heat obtainable 
 from equal weights of condensed steam, and of water, 
 reducing both from the temperature of 2 1 2° to 60°, 
 to be as 7*425 to 1 ; but for equal bulks, it will be 
 as 1 to 228 ; that is, bulk for bulk, water will give 
 out 228 times as much heat as steam, on reducing 
 both from the temperature of 2 1 2° to 60°. A given 
 bulk of steam will therefore lose as much of its heat 
 in one minute, as the same bulk of water will lose 
 in three hours and three quarters. 
 
 67. When the water and the steam are both 
 contained in iron pipes, the rate of cooling will, 
 however, be very different from this ratio ; in conse- 
 quence of the much larger quantity of heat which 
 is contained in the metal itself, than in the steam 
 with which the pipe is filled. 
 
 ^ The results of different experiments on the subject of the 
 latent heat of steam, although somewhat various, are yet suffi- 
 ciently near for all practical purposes. Watt's experiments give 
 900° to 950°; Lavoisier and Laplace, 1000°; Mr. Southern 945°; 
 Dr. Ure, 967° to 1000°; and Count Rumford, 1000°. 
 
60 
 
 PERMANENCE OF 
 
 68. The specific heat of cast-iron being nearly 
 the same as water (see Table V.) ; if we take two 
 similar pipes, 4 inches diameter, and ^ of an inch 
 thick, one filled with water, and the other with 
 steam, each at the temperature of 212°; the one 
 which is filled with water will contain 4*68 times as 
 much heat as that which is filled with steam : there- 
 fore if the steam pipe cools down to the tempera- 
 ture of 60° in one hour, the pipe containing water 
 would require four hours and a half, under the same 
 circumstances, before it reached the like tempera- 
 ture. But this is merely reckoning the effect of the 
 pipe and of the fluid contained in it. In a steam 
 apparatus this is all that is effective in giving out 
 heat : but in a hot- water apparatus, there is likewise 
 the heat from the water contained in the boiler, and 
 even the heat from the brick work around the 
 boiler ; which all tends to increase the effect of the 
 pipes, in consequence of the circulation of the water 
 continuing long after the fire is extinguished; in 
 fact, as long as ever the water is of a higher tem- 
 perature than the surrounding air of the room. 
 From these causes, the difference in the rate of 
 cooling, of the two kinds of apparatus, will be nearly 
 double what is here stated : so that a building 
 warmed by hot water, will maintain its tempera- 
 ture, after the fire is extinguished, about six or 
 eight times as long as it would do if it were heated 
 with steam. 
 
TEMPERATURE. 
 
 61 
 
 69. This is an important consideration wherever 
 permanence of temperature is desirable ; as, for 
 instance, in hot-houses, conservatories, and other 
 buildings of a similar description : and even in the 
 application of this invention to the v^^arming of 
 dwelling-houses, manufactories, &c.; this property, 
 which water possesses, of retaining its temperature 
 for so long a time, and the very great amount of its 
 specific heat, prevents the necessity for that constant 
 attention to the fire, which has always been found 
 so serious an objection to the general use of steam 
 apparatus. 
 
 70. The velocity with which a pipe or any other 
 vessel cools, when filled with a heated fluid, depends 
 principally upon two circumstances — the quantity 
 of fluid that it contains, relatively to its surface ; 
 and the temperature of the air by which it is 
 surrounded ; or, in other words, the excess of tem- 
 perature of the heated body, above that of the 
 surrounding medium. The subject of the radiation 
 of heat, and the rate at which a heated body cools, 
 under various circumstances, will be fully considered 
 in another chapter. But for temperatures below the 
 boiling point of water, and under such circum- 
 stances as we are now considering with regard to 
 hot-water pipes, the velocity of cooling may be esti- 
 mated simply in the ratio of the excess of heat, 
 which the heated body possesses above the tempe- 
 rature of the surrounding air. The variation in the 
 
G2 
 
 RATE OF 
 
 rate of cooling, arising from a difference of the 
 superficies to the mass, is, for bodies of all shapes, 
 inmrsely^ as the mass divided hy the superficies. There- 
 fore, the relative ratios of cooling, for any two 
 bodies of different shapes and temperatm-es, is the 
 inverse numbers obtained by dividing the mass by 
 the superficies, multiplied by the direct excess of 
 heat above the surrounding air ; provided the tem- 
 perature of the heated bodies be below 212°. Thus 
 suppose the relative ratio of cooling be required, for 
 two cisterns filled with hot water, one a cube of 18 
 inches, at the temperature of 200°; the other a 
 parallelepiped, 24 inches long, 15 inches wide, and 
 3 inches deep, at the temperature of 170°; the sur- 
 rounding air in both cases being 60°. Then, as, 
 
 INCHES. INCHES. 
 
 The cube contains 5832, divided by 1944, the superficies = .3* 
 
 The parallelepiped contains . 1080, do. 954, do. =113 
 
 The inverse of these numbers is, to call the cube 
 1-13, and the parallelepiped 3*0. Then multiply 
 1*13 by 140 (the direct excess of temperature of 
 the cube), and the answer is 158*2 : and multiply 
 3*0 by 110 (the direct excess of temperature of the 
 parallelepiped), and the answer is 330*0. There- 
 fore, the parallelepiped will cool, in comparison with 
 the cube, in the proportion of 330 to 158, or as 
 2*08 to 1 : so that if it requires two hours to cool 
 the cube, a half, or a quarter, or any other propor- 
 tional part of its excess of heat, the other vessel will 
 
COOLING. 
 
 63 
 
 lose the same proportional part of its excess of heat 
 in one hour. 
 
 71. It is evident that these different velocities of 
 cooling, are quite independent of the effect that the 
 respective bodies will produce, in warming a given 
 space; for as the cube contains upwards of six 
 times as much water as the other vessel, so it would 
 warm six times as much air, if both vessels were of 
 the same temperature. But if six of the oblong 
 vessels were used, they would heat just the same 
 quantity of air as the cube; but the latter would 
 require rather more than 2^ hours, to do what the 
 oblong vessels would accomplish in one hour, suppo- 
 sing the temperature to be the same in both cases. 
 In the previous example, the temperatures are sup- 
 posed to be different : otherwise the relative ratio 
 of cooling, of the two vessels, would have been as 
 2^ to 1, instead of 2 to 1 as stated. 
 
 72. In estimating the cooling of round pipes, the 
 relative ratio is very easily found ; because the in- 
 verse number of the mass divided hy the superficies^ is 
 exactly equal to the inverse of the diameters. There- 
 fore, supposing the temperature to be alike in all, 
 
 If the diameter of the pipes be - 1. 2. 3. 4 inches. 
 The ratio of cooling will be - - 4. 2. 1*3. 1 
 
 That is, a pipe of 1 inch diameter will cool four 
 times as fast as a pipe of 4 inches diameter; and so 
 on with the other sizes. These ratios, multiplied 
 
64 
 
 SIZE OF PIPES. 
 
 by the excess of heat which the pipes possess above 
 that of the air, will give the relative rate of cooling 
 when their temperatures are different, supposing 
 they are under 2 1 2° of Fahrenheit : but if the tem- 
 peratures are alike in all, the simple ratios given 
 above, will show their relative rate of cooling, with- 
 out multiplying by the temperatures. When the 
 pipes are much above 212°, as, for instance, with 
 the High Pressure system of heating, the ratio of 
 cooling must be calculated by the rules given in the 
 Vlth Chapter. 
 
 73. The unequal rate of cooling of the various 
 sizes of pipes, renders it necessary to consider the 
 purpose to which any building is to be applied, that 
 is required to be heated on this plan. If it be 
 desired that the heat shall be retained for a great 
 many hours after the fire is extinguished, then large 
 pipes will be indispensable ; but if the retention of 
 heat be unimportant, then small pipes may be 
 advantageously used. It may be taken as an inva- 
 riable rule, that, in no case, should pipes of greater 
 diameter than 4 inches be used, because, when they 
 are of a larger size than this, the quantity of water 
 they contain is so considerable, that it makes a great 
 difference in the cost of fuel, in consequence of the 
 increased length of time required to heat them. 
 (See art. 156.) For hot-houses, green-houses, con- 
 servatories, and such like buildings, pipes of 4 inches 
 diameter will generally be found the best ; though 
 
SIZE OF BOILERS. 
 
 65 
 
 occasionally, pipes of 3 inches diameter may be used 
 for such purposes, but never any of a smaller size. 
 In churches, dwelling-houses, manufactories, &c. 
 pipes of either 2 or 3 inches diameter will, perhaps, 
 upon the whole, be found the most advantageous; 
 for they will retain their heat sufficiently long for 
 ordinary purposes, and their temperature can be 
 sooner raised, and to more intensity, than larger 
 pipes : and, on this account, a less number of super- 
 ficial feet will suffice to warm a given space. 
 
 74. Tn adapting the boiler to a hot water ap- 
 paratus, it is not necessary, as is the case with a 
 steam boiler, to have its capacity exactly propor- 
 tional to that of the total quantity of pipe which 
 is attached to it : on the contrary, it is some- 
 times desirable even to invert this order, and to 
 attach a boiler of small capacity to pipes of large 
 size. It is not, however, meant, in recommending 
 a boiler of small capacity, to propose also that it 
 should be of small superficies; for it is indispen- 
 sable that it should present a large surface to the 
 fire, because, in every case, the larger the surface on 
 which the fire acts, the greater will be the economy 
 in fuel, and, therefore, the greater will be the effi^ct 
 of the apparatus. 
 
 75. The sketches of the boilers, figs. 13, 14, 15, 
 16, 17, & 18, and the section of the circular boiler, 
 fig. 19, are several diflferent forms which present 
 
 F 
 
66 SHAPE OF BOILERS. 
 
 various extents of surface in proportion to their 
 capacity. 
 
 Fig. 13. Fig. 14. Fig. 15. Fig. 16. 
 
 Fig. 17. Fig. 18. Fig. 19. 
 
 All except the two first, however, have but a 
 small capacity, relatively to their superficies, com- 
 pared with boilers which are used for steam. There 
 is no advantage whatever gained by using a boiler 
 which contains a large quantity of water; for, 
 as the lower pipe brings in a fresh supply of water, 
 as rapidly as the top pipe carries the hot water, 
 off, the boiler is always kept absolutely full. The 
 only plausible reason which can be assigned for 
 using a boiler of large capacity, is, that as the 
 apparatus then contains more water, it will retain 
 its heat a proportionably longer time. This, though 
 true in fact, is not a sufficient reason for using such 
 boilers: for the same end can be accomplished, 
 
SHAPE OF BOILERS. 
 
 67 
 
 either by using larger pipes, or by having a tank, 
 connected with the apparatus, which can be so 
 contrived, by being enclosed in brick, or wood, or 
 some other non-conductor, as to give off very little 
 of its heat by radiation, and yet to be a reservoir of 
 heat for the pipes after the fire has been extinguished. 
 If this tank communicates with the rest of the 
 apparatus by a stop-cock, the pipes can be made to 
 produce their maximum effect in a much shorter 
 time than if this additional quantity of water had 
 been contained in the boiler; and a more econo- 
 mical and efficient apparatus will be obtained. The 
 circulation will likewise be more rapid from 
 a boiler which contains but a small quantity of 
 water ; because the fire will have greater effect upon 
 it, and will render the water which is contained in 
 it, relatively lighter than that which is in the 
 descending pipe. 
 
 76. In proposing the adoption of boilers of small 
 capacity, however, it is necessary to accompany the 
 recommendation with a caution against running into 
 extremes ; for this error has been the cause of the 
 inefficiency of apparatus in many instances. The 
 sketch, fig. 1 8, is an instance of this sort, in which an 
 absurd extreme has occasionally been adopted. The 
 contents of a boiler of this shape, sometimes does 
 not exceed a couple of gallons, even when applied 
 to a very large furnace; and though this boiler 
 presents a large surface to the fire, the space allowed 
 
 F 2 
 
68 
 
 REPULSION OF WATER 
 
 for the water is so small, that the neutral salts and 
 alkaline earths, deposited by the water which evapo- 
 rates from the apparatus, contracts the water-way, 
 already far too small, and effectually impedes the 
 circulation, and also prevents the full force of the 
 fire from acting on the water. 
 
 77. But perhaps the more immediate cause of 
 failure, of this shaped boiler, arises in a different 
 way. The quantity of water which it contains 
 being so very small, and the heat of the fire, there- 
 fore, very intense upon it, a repulsion is caused 
 between the iron and the water, and the latter does 
 not receive the full quantity of heat. This extraor- 
 dinary effect is not hypothetical : it has been proved 
 to exist, by the most satisfactory experiments ; 
 particularly some which were made by the Members 
 of the Franklin Institution of Pennsylvania. The 
 repulsion between heated metals and water, they 
 ascertained to exist, to a certain extent, even at 
 very moderate degrees of heat ; being appreciably 
 different at various temperatures, below the boiling 
 point of water. But, as the temperature rises, the 
 repulsion increases with great rapidity ; so that iron, 
 when red hot, completely repels water, scarcely com- 
 municating to it any heat, except, perhaps, when 
 under considerable pressure. 
 
 78. The boiler in question, however, seldom or 
 never reaches the temperature of luminosity, though 
 it is still sufficiently high to make a considerable 
 
BY HOT IRON. 
 
 69 
 
 difference in the heating of the water. Added to 
 this, the form of it prevents the full effect of the heat 
 being communicated to the pipes : for the extreme 
 smallness of the water way, prevents the rapid com- 
 munication between the various parts, and therefore 
 the upright, or flow pipe, receives its principal supply 
 of heat from that portion of the boiler immediately 
 underneath where it is fixed, instead of that equa- 
 ble communication of heat from all parts, which is 
 the ordinary process in boilers of good proportions. 
 There is likewise a probability that steam would 
 form in this boiler, which would still farther interfere 
 with the circulation of the water. But were the 
 water way to be enlarged, all these inconveniences 
 and probable causes of failure would proportionably 
 decrease. 
 
 79. Though all these causes of inefficient action 
 may not exist simultaneously, yet they may act at 
 different stages of the working of the apparatus. 
 But they all apply equally to every boiler, in which 
 the rational limits of the surface, relatively to the 
 size, have given place to wild chimeras and fan- 
 ciful notions, not based on sound principles of phi- 
 losophy. 
 
 80. It is obvious that the extent of surface which 
 a boiler ought to expose to the fire, should be pro- 
 portional to the quantity of pipe that is required to 
 be heated by it : and it is not difficult to estimate 
 these relative proportions with sufficient accuracy. 
 
70 
 
 SURFACE OF BOILERS 
 
 notwitlistanding the various circumstances which 
 modify the effect. Reckoning the surface which a 
 steam boiler exposes to the fire, at 4 square feet, for 
 each cubic foot of water evaporated per hour ^ ; and 
 calculating the latent heat of steam at 1000°; we 
 shall find that the same extent of boiler surface, 
 which would evaporate a cubic foot of water, of the 
 temperature of 52°, into steam, of which the tension 
 is equal to one atmosphere, would supply the requi- 
 site heat to 232 feet of pipe, 4 inches diameter, 
 when its temperature is to be kept at 140° above 
 that of the surrounding air. The following propor- 
 tions for the surface which a boiler for a hot-water 
 apparatus ought to expose to the fire, will be found 
 useful. 
 
 Surface of Boiler . ■ n- o • r»- o D v. 
 
 exposed to the Fire. 4 m. Pipe. 3 in. Pipe. 2 in. Pipe. 
 
 31 square feet, will heat 200 feet, or 266 feet, or 400 feet. 
 
 5i 300 . . 400 . . 600 
 
 7 ...... 400 . . 533 .. 800 
 
 8i 500 . . 666 . . 1000 
 
 12 700 . . 933 . . 1400 
 
 17 1000 . . 1333 . . 2000 
 
 81. A small apparatus ought, perhaps, to have 
 rather more surface of boiler, in proportion to the 
 
 ' The surface of a steam boiler which it is necessary to expose 
 to the action of the fire, in order to evaporate one cubic foot of 
 water per hour, varies from 2 to 10 square feet, according to the 
 rapidity of the draught, and the intensity of the heat of the 
 furnace. When the very small surfaces are used, mechanical 
 means are requisite for blowing the fire. 
 
EXPOSED TO THE FIRE. 
 
 71 
 
 length of pipe, than a larger one ; as the fire is less 
 intense, and burns to less advantage in a small, than 
 in a large furnace. It depends, however, upon a 
 variety of circumstances, whether it will be expe- 
 dient to increase the quantity of pipe, in proportion 
 to the surface of the boiler, beyond what is here 
 stated; for although many causes tend to mo- 
 dify the eifect, the above calculation will be found 
 a good average proportion, under ordinary circum- 
 stances. The effect depends greatly upon the quality 
 of the coal, the height of the chimney, the rapidity 
 of draught, the construction of the furnace, and 
 many other particulars ; but it will always be found 
 more economical, as regards the consumption of 
 fuel, to work with a larger surface of boiler at a 
 moderate heat, than to keep the boiler at its maxi- 
 mum temperature. 
 
 82. But beside all these causes that modify the 
 effect, there is another that will greatly alter the 
 proportions which may be employed. The data 
 from which the calculation of the boiler surface is 
 made, assumes the difference to be 1 40° between the 
 temperature of the pipe and the air of the room 
 which is heated ; the pipe being 200°, and the air 60°. 
 But if this difference of temperature be reduced, 
 either by the air in the room being higher, or by 
 the apparatus being worked below its maximum 
 temperature ; then, in either case, a given surface of 
 boiler will suffice for a greater length of pipe. For 
 
72 
 
 SURFACE OF BOILERS 
 
 if the difference of temperature between the water 
 and the air, be only 120°, instead of 140°, the same 
 surface of boiler will supply the requisite degree of 
 heat to ^ more pipe; and if the difference be only 
 100°, the same boiler will supply above ^ more 
 pipe than the quantity before stated. It will, there- 
 fore, frequently occur in practice, that the quantity 
 of pipe in proportion to a given surface of boiler, 
 may be considerably increased beyond the amount 
 which is given in the preceding Table : because, in 
 forcing houses, for instance, the temperature of the 
 air will always be above 60° ; and in the warming of 
 churches, workhouses, or other large buildings, the 
 temperature of the water will generally be consi- 
 derably below 200° — the pipe not being required 
 to be worked at its greatest intensity — and, 
 therefore, in both these instances, a larger propor- 
 tion of pipe may safely be applied to a given sized 
 boiler. 
 
 83. In order to estimate the quantity of surface, 
 which is acted upon by the fire, an allowance 
 must be made for the flues which circulate round 
 the exterior of the boiler. Thus, suppose the boiler, 
 fig. 1 5, to be 30 inches long ; there will be about 
 8{- square feet of surface exposed to the direct action 
 of the fire : and suppose also there are four exter- 
 nal flues, one on each side, and two on the top of 
 the boiler, each being 1 2 inches wide ; we may reckon 
 that one half the effect is produced by these flues. 
 
EXPOSED TO THE FIRE. 
 
 73 
 
 which would have obtained, had the direct action of 
 the fire been employed on the like extent of sur- 
 face ; therefore the flues will be equal to 5 square 
 feet of surface exposed to the direct action of the 
 fire, making altogether 13f square feet, as the avail- 
 able heating surface of a boiler of this shape and 
 size. This would be sufficient to heat about 800 
 feet of pipe 4 inches diameter, when the excess of 
 its temperature above that of the surrounding air, is 
 140°, as before stated. A boiler of the same shape, 
 and 24 inches long, has about 1 1 square feet of sur- 
 face, when calculated by the preceding rule : a boiler 
 36 inches long, has \Q\ square feet of surface ; and 
 a boiler 42 inches long has 19 square feet of surface; 
 the increase being directly proportional, in the sim- 
 ple ratio, to the length. 
 
 84. A circular boiler 30 inches diameter, like fig. 
 19, with a 9-inch circular flue round the outside, will 
 expose, as nearly as possible, the same extent of sur- 
 face as a boiler 30 inches long, of the shape last de- 
 scribed ; and therefore the one will be as effective as 
 the other. The surface of other sizes of this shaped 
 boiler can be easily calculated ; but instead of vary- 
 ing in the simple ratio of the length or diameter, it 
 will be found to be proportional to the square of the 
 diameter^ so that the proportion of surface increases 
 more rapidly than in the arched boiler. Thus a 
 circular boiler 24 inches diameter, has 8f square 
 
74 
 
 SURFACE OF BOILERS. 
 
 feet of surface exposed to the fire ; a 30-inch has 
 13f square feet; a 36-inch, 19f square feet; and a 
 42-inch, 26 1 square feet: the small sizes having 
 less surface, and the large sizes having more, than 
 the arched boilers of the shape of fig. 15. 
 
CHAPTER V. 
 
 On the Construction and Dimensions of Furnaces. 
 
 85. Although the construction of the furnace for 
 a hot-water apparatus, is a matter of some import- 
 ance, it is not intended to enter here at any great 
 length into the subject. To investigate the various 
 inventions for furnaces which have been brought 
 forward, would occupy much space ; and such a 
 course of inquiry appears to be unnecessary, because 
 most persons who erect hot-water apparatus have 
 had some experience in the construction of the 
 ordinary descriptions of fire-work, and this, in fact, 
 is all that is needful, or indeed desirable, for fur- 
 naces which are used for this purpose. The in- 
 tense heat that is required for some descriptions 
 of steam-engine furnaces is here unnecessary ; but 
 a moderate heat, economically applied, and the 
 furnace constructed so that the fuel shall burn for 
 several hours without attention is the object to be 
 attained, and which is by no means difficult to 
 accomplish, with a moderate degree of care. 
 
76 
 
 CONSTRUCTION OF 
 
 86. The difficulties which attend the erection of 
 furnaces for a hot-water apparatus, are comparatively 
 trifling to those required for steam boilers. When 
 a boiler is required to supply pipes for warming a 
 building by steam, its size must be much larger than 
 one for warming the same building with hot water. 
 In the former case the capacity of the boiler must 
 be considerably larger than that of the whole 
 length of pipe : in the latter, its capacity may be 
 half, or a quarter, or a tenth, or even a twentieth 
 of the capacity of the pipes, without causing any 
 diminution of the effect, provided (art. 76) this re- 
 duction in the size of the boiler, be not carried to an 
 extravagant length. 
 
 87. In large steam boiler furnaces, in order to 
 permit of the flue extending round the boiler, an 
 extremely brisk fire and rapid draught are required, 
 otherwise the heated and inflamed gases will not be 
 of a sufficiently high temperature to impart heat to 
 the boiler ; but they will, in fact, before completing 
 the circuit of the flues, and reaching the chimney, 
 act as a cold body, and abstract heat from the boiler 
 instead of imparting it. No such difficulty, however, 
 occurs with boilers for hot water apparatus. A very 
 moderate draught will suffice to carry the heated 
 smoke, and inflamed gases, round a boiler of the 
 comparatively limited size which is here required; 
 and they will act as a heating body to a boiler of 
 this kind, when at a temperature which would make 
 
FURNACES. 
 
 77 
 
 it act as a cold body to a steam boiler ; because, in 
 the latter case, the water is seldom of a less tem- 
 perature than 220° to 230°, while, in the former, it 
 is rarely above 180° to 200°. 
 
 88. Passing over then, as unnecessary for the 
 present purpose, many ingenious forms which have 
 been given to furnaces, it will be sufficient to 
 describe the simple plan of construction which is 
 most usually adopted. 
 
 The heat should be confined within the furnace 
 as much as possible, by contracting the farther 
 end of it, at the part called the throat, so as to 
 allow only a small space for the smoke and inflamed 
 gases to pass out. The only entrance for the air 
 should be through the bars of the grate, and the 
 heated gaseous matter will then pass directly upward 
 to the bottom of the boiler, which will act as a 
 reverbatory, and cause a more perfect combustion of 
 the fuel than would otherwise take place. The 
 lightness of the heated gaseous matter causes it to 
 ascend the flue, forcing its passage through the 
 throat of the furnace with a velocity proportional to 
 the smallness of the passage, the vertical height of 
 the chimney, and the levity of the gases, arising 
 from their expansion by the heat of the furnace. 
 
 89. In this arrangement, the whole of the air 
 which supports the combustion passes through the 
 fire from below ; and any air admitted at the furnace 
 door, between the fuel and the boiler, reduces the 
 
78 
 
 ADMISSION OF AIR. 
 
 intensity of the heat. The only case where the 
 admission of air above the fuel will be at all 
 advantageous, is when coal which emits a vast 
 quantity of flame is used, and which, therefore, 
 contains a large quantity of hydrogen, and propor- 
 tionably less oxygen, than Newcastle coal. Some 
 of the Staffordshire and Scotch coals are of this 
 description ; and here, a portion of air admitted at 
 the top of the fuel, will promote the more perfect 
 combustion of the gaseous products of the coal. 
 But, even in this case, less heat will be received by 
 the boiler, in a given time, unless the air be warmed 
 before it enters the furnace ; for as air will not 
 support combustion until it attains a temperature of 
 from 900° to 1000°, of Fahrenheit, if a current of cold 
 air passes between the fuel and the boiler, a certain 
 portion of heat is required to raise the temperature 
 of the air, which heat would, otherwise, have been 
 received directly by the boiler. 
 
 90. In all ordinary cases, then, the greatest 
 economy, as well as the greatest effect, will be pro- 
 duced by admitting air only through the ash-pit of 
 the furnace ; and the rapidity of combustion of the 
 coal will depend upon the quantity of air admitted 
 through the bars, and upon the velocity of its ad- 
 mission. 
 
 91. The quantity of coal which is required to be 
 burnt in each particular furnace, must determine 
 the area of the bars : and as this been ascertained 
 
 1 
 
DIMENSIONS OF BARS. 
 
 79 
 
 experimentally for steam boilers, it is merely neces- 
 sary to reduce it to a standard suitable for a hot 
 water boiler. Supposing the ordinary kind of fur- 
 nace bars to alford about 30 inches of opening for the 
 air, in each square foot of surface — measured as the 
 bars are placed in the furnace, and allowing half-inch 
 openings between the bars, when the bars them- 
 selves are about 1^ inches wide, — then the relative 
 proportions between the area of the bars and the 
 length of pipe should be as follows : — 
 
 Area of Bars. 4 in. Pipe. 3 in. Pipe. 2 in. Pipe, 
 
 75 Square inches will supply 150 feet, or 200 feet, or 300 feet. 
 
 100 200 . . 266 . . 400 . . 
 
 150 300 . . 400 . . 600 . . 
 
 200 400 . . 533 . . 800 . . 
 
 250 500 .. 666 . . 1000 . . 
 
 300 600 . . 800 . . 1200 . . 
 
 400 800 . . 1066 . . 1600 . . 
 
 500 1000 . . 1333 . . 2000 . . 
 
 Thus, suppose there are 600 feet of pipe, 4 inches 
 diameter, in an apparatus ; then the area of the bars 
 should be 300 square inches : so that 13 inches in 
 breadth and 23 inches in length will give the requi- 
 site quantity of surface. But when it is required 
 to obtain the greatest heat in the shortest time, the 
 area of the bars should be increased, so that a larger 
 fire may be produced*. 
 
 ' The above proportions for the area of the bars may, in many 
 cases, be considerably reduced, particularly in the larger appa- 
 ratus ; because these proportions are calculated to give the maxi- 
 
80 
 
 SIZE OF FURNACES. 
 
 92. In order to make the fire burn for a lonjr 
 time without attention, the furnace should extend 
 beyond the bars both in length and breadth ; and 
 the coals which are placed on this blank part of the 
 furnace, in consequence of receiving no air from 
 below, will burn very slowly, and will only enter 
 into complete combustion when the coal which lies 
 directly on the bars has burned away. 
 
 93. This plan of constructing furnaces is so well 
 known as scarcely to need further description : it 
 may, however, be observed, that the size of this 
 blank, or dumb part of the furnace, should be com- 
 parative to the length of time the fire is required 
 to burn ; being larger or smaller in proportion as the 
 fire is required to burn for a longer or a shorter 
 period. As the maximum effect of the furnace is but 
 seldom required, the register to the ash-pit door, 
 and the damper to the chimney, must be used to 
 regulate the draught, and thus limit the consumption 
 of fuel. 
 
 94. The relative sizes of the furnace bars, and of 
 the boiler, which have been stated in this and the 
 preceding chapter, are all given with reference to 
 certain lengths of pipe, which they will respectively 
 heat. But to complete the calculations, it is neces- 
 sary to ascertain the actual amount of heat which 
 
 mum effect, and in many cases this is never required : a less 
 quantity of coal will, therefore, be used, and, of course, a less area 
 of the bars will be sufficient. 
 
SIZE OF FURNACES. 
 
 81 
 
 a given quantity of pipe will afford, under the 
 various circumstances which occur in the application 
 of it to the warming of buildings of different de- 
 scriptions. Before entering into this inquiry, how- 
 ever, it may be necessary to premise some observa- 
 tions on the general laws of heat. 
 
 G 
 
CHAPTER VI. 
 
 General Laws of Heat — Radiation and Conduction — Law of 
 Cooling in Air and other Gases — Ratio of Cooling — Law of 
 Cooling by Radiation — Laws of Radiation — Effect of Surface 
 on Radiation — Effect of Colour on Radiation — Capacity of 
 Bodies for Caloric. 
 
 95. However various are the methods by which 
 artificial heat is distributed in the warming of build- 
 ings, they are all subject to certain conditions, which 
 constitute the primary laws of heat; and in the 
 present chapter some of these laws, which bear upon 
 the subject before us, will be considered. 
 
 96. Heated bodies give off their caloric by two 
 distinct modes, — radiation and conduction. These 
 are governed by different laws ; but the rate of 
 cooling by both modes increases considerably in pro- 
 portion as the heated body is of a greater tempera- 
 ture above the surrounding medium. This variation 
 was long supposed to be exactly proportional to the 
 simple ratio of the excess of heat ; that is to say, 
 supposing any quantity of heat given off in a certain 
 time at a specified difference of temperature, at 
 double that difference, twice the quantity of heat 
 would be given off in the same time. This law was 
 
LAWS OF HEAT. 
 
 83 
 
 originally proposed by Newton in the Principia; 
 and, although rejected as erroneous by some philo- 
 sophers, it was followed by Richmann, Kraft, Dalton, 
 Leslie, and many others, and was usually considered 
 accurate, until the masterly and elaborate experi- 
 ments of M. M. Petit and Dulong proved that, 
 though approximately correct for low temperatures, 
 it becomes extremely inaccurate at the higher de- 
 grees of heat ^ 
 
 97. The cooling of a heated body, under ordi- 
 nary circumstances, is evidently the combined effects 
 of radiation and conduction. The conductive power 
 of the air is principally owing to the extreme mo- 
 bility of its particles ; for, otherwise, it is one of the 
 worst conductors we are acquainted with ; so that, 
 when confined in such a manner as to prevent its 
 freedom of motion, it is a most useful non-con- 
 ductor. 
 
 98. The proportion which radiation and con- 
 duction bear to each other, has in general been very 
 erroneously estimated. Count Rumford considered 
 the united effect, compared with radiation alone, 
 was as 5 to 3 ; and Franklin supposed it to be as 
 5 to 2. 
 
 ' As the present inquiry relates merely to simple heat, the 
 recent important experiments of Nobili and Melloni on radiation 
 by luminous hot bodies — which prove the existence of two 
 distinct kinds of heating rays given off at the same time from the 
 same body — do not affect the question ; as it is only at a tem- 
 perature amounting to luminosity, that these effects occur. 
 
 g2 
 
84 
 
 LAWS OF HEAT. 
 
 99. No such general law, however, can be de- 
 duced ; for the relative proportions vary with the 
 temperature, and with the peculiar substance or 
 surface of the heated body. For, while the cooling 
 effect of the air hy conduction is the same on all sub- 
 stances, and in all states of the surface of those sub- 
 stances, — radiation varies materially, according to 
 the nature of the surface. 
 
 100. The influence of the air, by its power of 
 conduction, varies also with its elasticity or barome- 
 tric pressure. The greater its elastic force, the 
 greater also is its cooling power, according to the 
 following law : — When the elasticity of the air varies 
 in a geometrical progression, whose ratio is 2, its cool- 
 ing power changes likewise in a geometrical progression, 
 whose ratio is 1*366. 
 
 101. The same law holds with all gases, as well 
 as with atmospheric air ; but the ratio of the pro- 
 gression varies for each gas. 
 
 102. To show the relative velocities of cooling, 
 at different temperatures, the following table, con- 
 structed from the experiments of Petit and Dulong, 
 is given. The first column shows the excess of 
 temperature^ of the heated body above the sur- 
 
 * The temperatures in this chapter are all expressed in degrees 
 of the Centigrade thermometer. As the zero of this thermometer is 
 the freezing point of water, and from that to the boiling point of 
 the same fluid is 100°; — in order to find the number of degrees 
 of Fahrenheit's scale, which answers to any given temperature of 
 the Centigrade, multiply the number of degrees of Centigrade by 
 
LAWS OF HEAT. 
 
 85 
 
 rounding air; the second column shows the rate of 
 cooling of a thermometer with a plain bulb ; and 
 the third column gives the rate of cooling when the 
 bulb was covered with silver leaf. The fourth 
 column shows the amount due to the cooling of the 
 air alone ; and by deducting this from the second 
 and third columns respectively, we shall find what 
 is the amount of radiation, under the two different 
 states of surface, noticed at the top of the second and 
 third columns. 
 
 Excess of 
 Temperature of 
 the Thermometer 
 above that of 
 the Air : 
 Centigrade Scale. 
 
 Total Velocity 
 of cooling of the 
 naked Bulb. 
 
 Total Velocity 
 
 of cooling 
 of Bulb covered 
 with Silver Leaf. 
 
 Amount of 
 cooling due to 
 Conduction of 
 the Air alone. 
 
 260° 
 
 24-42 
 
 10-96 
 
 8-10 
 
 240° 
 
 21-12 
 
 9-82 
 
 7-41 
 
 220° 
 
 17-92 
 
 8-59 
 
 6-61 
 
 200° 
 
 15-30 
 
 7-57 
 
 5-92 
 
 180° 
 
 13-04 
 
 6-57 
 
 5-19 
 
 160° 
 
 10-70 
 
 5-59 
 
 4-50 
 
 140° 
 
 8-75 
 
 4-61 
 
 3-73 
 
 120° 
 
 6-82 
 
 3-80 
 
 3-11 
 
 100° 
 
 5-57 
 
 3-06 
 
 2-53 
 
 80° 
 
 4-15 
 
 2-32 
 
 1-93 
 
 60° 
 
 2-86 
 
 1-60 
 
 1-33 
 
 40° 
 
 1-74 
 
 •96 
 
 •80 
 
 20° 
 
 •77 
 
 •42 
 
 •34 
 
 10° 
 
 -37 
 
 •19 
 
 •14 
 
 9, and divide the product by 5 ; add 32 to the quotient thus 
 obtained, and this sum will be the number of degrees of FahreU' 
 heit required. As, however, in the above table, the temperatures 
 given are only the excess, and not the absolute temperatures, 
 the 32° to be added by this rule must be omitted. 
 
86 
 
 LAWS OF HEAT. 
 
 103. Some very remarkable effects may be per- 
 ceived by an inspection of the above table. It 
 appears that the ratio of heat lost by contact of the 
 air alone, is constant at all temperatures ; that is, 
 whatever is the ratio between 40° and 80°, for in- 
 stance, is also the ratio between 80° and 160°, or 
 between 100° and 200°. This law is expressed by 
 the formula, — 
 
 v = n. t 
 
 where t represents the excess of temperature, and 
 n a number which varies with the size of the heated 
 body. In the case represented in the foregoing 
 table w=z 0-00857. 
 
 104. Another remarkable law is, that the cooling 
 effect of the air is the same, for the like excess of heat, 
 on all bodies without regard to the particular state or 
 nature of their surface. This was ascertained by 
 Petit and Dulong, in a series of experiments not 
 necessary here to detail, but which abundantly prove 
 the accuracy of the deduction ^ 
 
 105. By comparing the second and third columns 
 in the above table, it will be immediately perceived 
 that the loss of heat by radiation (deducting the 
 cooling by conduction of the air given in the fourth 
 column) varies greatly with the nature of the radi- 
 ating surface ; though, whatever be the nature of the 
 
 ^ Annals of Philosophy, vol. xiii. 
 
LAWS OF HEAT. 
 
 87 
 
 surface, the loss of heat follows the same law in all casesy 
 though in a different ratio, 
 
 106. It should be observed that, in this table, 
 the second, third, and fourth columns show the 
 number of degrees of heat which were lost per 
 minute, by the body which was the subject of expe- 
 riment ; and, therefore, these numbers represent the 
 velocity of cooling. 
 
 107. When the numbers in the last column 
 are deducted from those in the second and third 
 columns, the difference will show the loss of heat by 
 radiation, for the plain and silvered bulb respect- 
 ively ; the fourth column being the loss by conduc- 
 tion of the air, which is the same for all surfaces. 
 It will immediately be perceived, therefore, that the 
 loss of heat by conduction and by radiation, bear no 
 constant ratio to each other. But, while conduction 
 proceeds by a regular geometrical progression, radiation 
 follows another law, viz. when a body cools in vacuo 
 surrounded by a medium whose temperature is constant, 
 the velocity of cooling, for excess of temperature in 
 arithmetical progression, increases as the terms of 
 a geometrical progression, diminished by a constant 
 quantity. This law is represented by the formula, — 
 
 \-m.a' {a'—\) 
 
 where a is a constant quantity for all bodies 
 = 1*0077 ; t the excess of temperature of the radi- 
 ating body ; the temperature of the surrounding 
 
88 
 
 LAWS OF HEAT. 
 
 medium ; and m a coefficient which varies with the 
 size and nature of the radiating body, to be deter- 
 mined for each particular case. It will likewise 
 appear that, when we compare the total cooling of 
 two different surfaces, the law is more rapid at low 
 temperatures, and less rapid at high temperatures, 
 for the body which radiates the least, in comparison 
 with that which radiates with greater power. 
 
 108. But the cooling of a body by conduction 
 of the air, differs from the effect of radiation in a 
 remarkable manner in this particular ; — that, while 
 the ratio of loss hy conduction continues the same, for 
 the same excess of temperature, whatever be the absolute 
 temperatures of the air and heated body, — radiation 
 increases in velocity, for like ej?cess of temperature, 
 when the absolute temperatures of the air and heated 
 body increase. The following table shows the law of 
 cooling by radiation, for the same body at different 
 temperatures : 
 
 Excess of 
 
 Velocity of Cooling when the suiTounding medium is at 
 
 Temperature 
 
 the undermentioned Temperatures. 
 
 of the 
 
 
 
 
 
 Thermometer. 
 
 0° 
 
 20° 
 
 40° 
 
 60° 
 
 220° 
 
 8-81 
 
 10-41 
 
 11-98 
 
 
 200° 
 
 7-40 
 
 8-58 
 
 10-01 
 
 11-64 
 
 180° 
 
 6-10 
 
 704 
 
 8-20 
 
 9-55 
 
 160° 
 
 4-89 
 
 5-67 
 
 6-61 
 
 7-68 
 
 140° 
 
 3-88 
 
 4-57 
 
 5-32 
 
 6-14 
 
 120° 
 
 3-02 
 
 3-56 
 
 4-15 
 
 4-84 
 
 100° 
 
 2 30 
 
 2-74 
 
 3-16 
 
 3-68 
 
LAWS OF HEAT. 
 
 89 
 
 It will be observed in this table, that, when the 
 absolute temperatures of the surrounding medium 
 and radiating body, are increased 20° of Centigrade, 
 the difference between their temperatures continuing the 
 same, the velocity of cooling is multiplied by 1*165, 
 which is the mean of all the ratios in the above 
 table, experimentally determined. 
 
 109. The total cooling of a body by radiation 
 and conduction, then, we shall find to be repre- 
 sented, under all circumstances, by this formula, — 
 
 m. (at — 1) -^n,f 
 
 The quantities a and h are constant for all bodies 
 and under all circumstances ; the first being 
 = 1-0077 and the latter = 1-233. The coeffi- 
 cient m will depend on the size and nature of the 
 heated surface, as well as upon the nature of the 
 surrounding medium. The coefficient n is inde- 
 pendent of the absolute temperature, as well as of 
 the nature of the surface of the body ; but will vary 
 with the elasticity and nature of the gas in which 
 the body is plunged : t is the excess of temperature 
 of the heated body, and Q the temperature of the 
 surrounding medium. 
 
 110. The fact, already adverted to, that the 
 ratio of cooling of those bodies that radiate least, is 
 more rapid at low temperatures, and less rapid at 
 high temperatures, than those bodies that radiate 
 
90 
 
 LAWS OF HEAT. 
 
 most, is perhaps one of the most remarkable of the 
 laws of cooling. It was first deduced experimentally 
 by Petit and Dulong, and it may be mathematically 
 proved from their formulae; but it is unnecessary 
 here to enter into the investigation. It appears, 
 however, that, when the total cooling of two bodies 
 is compared, the law is more rapid at low tempera- 
 tures, for the body which radiates least, and less 
 rapid, for the same body, at high temperatures ; 
 though separately for conduction and for radiation, 
 the law of cooling is, for the former, irrespective of 
 the nature of the body, and for the latter, that all 
 bodies preserve, at every difference of temperature, a 
 constant ratio in their radiating power. 
 
 111. To revert to the first table in this chapter. 
 We find the total cooling at 60° and 120° (of Centi- 
 grade), to be, about, as 3 to 7 ; at 60° and 180°, as 
 3 to 13 ; and at 60° and 240° as 3 to 21 : whereas, 
 according to the old law of Newton, they should 
 have been respectively as 3 to 6 ; as 3 to 9 ; and 
 as 3 to 12. But we find that the deviation in- 
 creases greatly with the increase of temperature, 
 and that when the ea^cess of temperature of the 
 heated body, above the surrounding air, is as high 
 as 240° of Centigrade (432° of Fahrenheit), the real 
 velocity of cooling is nearly double what it would 
 appear to be by the old and inaccurate law, varying, 
 however, with the nature of the surface. 
 
 112. But radiant heat is subject to other laws, 
 
 1 
 
LAWS OF HEAT. 
 
 91 
 
 beside those we have yet considered. Rays of heat 
 diverge in straight lines from every part of a heated 
 surface, and likewise from extremely minute depths 
 below the surface of hot bodies, being subject to the 
 laws of refraction the same as light. The intensity 
 of these rays decreases as the square of the distance, 
 and the emission of the rays is greatest in a line 
 perpendicular to the surface. The same law obtains 
 here, also, as with light, — that the eifect of the ray 
 is as the sine of the angle, which it forms with the 
 surface \ This law of the sines, first discovered by 
 Leslie, suggests a practical caution connected with 
 the subject before us, — namely, that the shape of the 
 pipes used to warm a building, is not wholly unimpor- 
 tant ; for, if flat pipes be used, and they be laid hori- 
 zontally, the major part of the radiated heat from the 
 
 1 Suppose 2; to be a body radi- 
 ating heat; x y a plane surface, 
 receiving two rays, radiated from 
 z, represented by the dotted lines 
 p, q. Then a, 5, is the sine of the 
 angle, the ray p forms, and c, d, 
 is the sine of the angle, the ray q 
 forms with the receiving surface. 
 
 The heating effect is greater in — 
 
 proportion as a 6 is longer than 
 c d: and if the ray proceeded in 
 a straight line, perpendicular to 
 the receiving surface, the effect would be the greatest possible. 
 
 The number of rays, radiated from any surface, is also found 
 to be greatest in a line perpendicular to the surface of the 
 radiating body. 
 
92 
 
 LAWS OF HEAT. 
 
 upper surface, will be received on the ceiling, and, 
 therefore, will produce but little beneficial effect. 
 The loss sustained in this way will be greater in 
 proportion to the higher temperature of the pipes, 
 for it will be seen by the table at the beginning 
 of this chapter, that the relative proportion which 
 radiation bears to conduction, increases with the 
 temperature : at the ordinary temperature of hot- 
 water pipes, about one-fourth the total cooling is 
 due to radiation. 
 
 113. The radiation of heat, we have already seen, 
 is greatly either increased or diminished, according 
 to the nature of the surface of the radiating body. 
 Professor Leslie has given the following as the 
 relative powers of radiation by different substances : 
 
 Lamp Black 100 
 
 Water (by estimate) 100 
 
 Writing Paper 98 
 
 Rosin 96 
 
 Sealing Wax 95 
 
 Crown Glass 90 
 
 China Ink 88 
 
 Ice 85 
 
 Red Lead 80 
 
 Isinglass 80 
 
 Plumbago 75 
 
 Thick Film of Oil 59 
 
 Film of Jelly . . • 54 
 
 Thinner Film of Oil 51 
 
 Tarnished Lead 45 
 
 Thin Film of Jelly (J of former) . . 38 
 
 Tin scratched with Sand-Paper ... 22 
 
 Mercury 20 
 
LAWS OF HEAT. 
 
 93 
 
 Clean Lead 19 
 
 Iron, polished 15 
 
 Tin Plate 12 
 
 Gold, Silver, and Copper 12 
 
 Thin Laminae of Gold, Silver, or Cop-l 
 per Leaf, on Glass J 
 
 114. As it has been established by the experi- 
 ments of M. M. Nobili and Melloni, as well as by 
 other experimentalists, that the radiating powers of 
 surfaces, for simple heat, are in the inverse order of their 
 conducting powers ; it follows that the above ratios of 
 radiating power, will by no means be proportional to 
 the total cooling of these respective bodies in air. 
 
 115. Professor Richmann, in order to ascertain 
 the conducting power of metals, enclosed thermo- 
 meters in hollow metallic vessels, which were heated 
 by being immersed in boiling water, until every part 
 had attained the same temperature. The heated 
 vessels were then exposed to the air, and their 
 times of cooling observed ; the difference in this 
 respect being considered as marking their conducting 
 power. The metals which appeared to have the 
 greatest power of retaining heat, were brass and 
 copper ; then iron and tin ; and lead the least of all. 
 The decrements of temperature in a given time being 
 as follows : 
 
 Lead ........ 25 
 
 Tin 17 
 
 Iron 11 
 
 Copper and Brass . . . . 10 
 
94 
 
 LAWS OF HEAT. 
 
 The result of this experiment must, however, neces- 
 sarily be inconclusive as regards conduction ; be- 
 cause the rate of cooling, under such circumstances, 
 would, if the bodies were extremely thin, be, in 
 fact, exactly proportional to their radiating powers, 
 which would prove nothing, a priori, as regards 
 conduction. The result would also vary materially 
 with the thickness of the metal. 
 
 116. The experiments of Ingenhausz and Dr. 
 Ure, on the same subject, were on a totally different 
 principle, and they vary but little from each other 
 in the results. They coated the ends of rods of 
 different metals with wax, and noted the time 
 required to melt it, when the opposite ends were 
 heated to a uniform temperature. Dr. Ure thus 
 found silver, to be by far the best conductor ; next 
 copper ; and then brass, tin, and wrought iron, 
 nearly equal ; then cast-iron and zinc ; and lead he 
 found by far the worst of all. 
 
 117. We might be led to conclude from all that 
 precedes, that those metals which are the worst con- 
 ductors, would be the most proper for vessels or 
 pipes, for radiating heat ; because, we find that the 
 heat lost by contact of the air, is the same for all 
 bodies, while those which radiate most, or are the 
 worst conductors, give out more heat in the same 
 time, than those bodies which radiate least, or are 
 good conductors. Such would be the case if the 
 vessels were infinitely thin ; but as this is not pos- 
 
LAWS OF HEAT. 
 
 95 
 
 sible, the slow conducting power of the metal, op- 
 poses an insuperable obstacle to the rapid cooling of 
 any liquid contained within it, by preventing the 
 exterior surface from reaching so high a tempera- 
 ture, as would that of a more perfectly conducting 
 metal, under similar circumstances; thus preventing 
 the loss of heat, both by contact of the air and by 
 radiation, the effect of both being proportional to 
 the excess of heat of the esterior surface of the 
 heated body. If a leaden vessel were infinitely thin, 
 the liquid contained in it would cool sooner than in 
 a similar vessel of copper, brass, or iron: but the 
 greater the thickness of the metal, the more appa- 
 rent becomes the deviation from this rule ; and, as 
 the vessels for containing water, must always have 
 some considerable thickness, those metals which are 
 the worst conductors, will oppose the greatest resist- 
 ance to the cooling of the contained liquid, although 
 apparently in opposition to the result of the prece- 
 ding experiments. 
 
 118. It is difficult on these grounds to account 
 for the effect which lead paint has in preventing the 
 free radiation of caloric, from bodies coated with it ; 
 because, in this case, the lead must be extremely 
 thin, and ought, therefore, to increase the amount of 
 radiation. The effect probably arises from the total 
 change of state which the lead undergoes by its 
 chemical combination with the carbonic acid, in the 
 process of making it into white lead. Practically, 
 
96 
 
 LAWS OF HEAT. 
 
 it is found to have an injurious tendency on the free 
 radiation of heat from most bodies ; varying, how- 
 ever, with their radiating powers. On a good radi- 
 ator, its effect is the most injurious, on a bad one, 
 less so : but its use should be avoided as much as 
 possible, in all cases where the free radiation of heat 
 is the object in view. 
 
 119. It is almost universally supposed that colour 
 has a considerable influence on radiant heat, and 
 also upon the absorption of heat — the two effects 
 being similar and equal. Sir H. Davy, by exposing 
 surfaces of various colours to the heat of the sun, 
 proved experimentally {Beddoe's Contributions, p. 
 44), that the absorbing power of different colours 
 was in this order ; — black, blue, green, red, yellow, 
 and white : black being the best, and white the 
 worst absorbent. In this order then, we should 
 expect to find the radiating powers of different co- 
 lours, and that by painting a body of a dark colour, 
 we should increase its power of radiation. This, 
 however, is not the case. There are the strongest 
 reasons for supposing that the absorption and radia- 
 tion of simple heat ; — that is, heat without light, or 
 heat from bodies below luminosity, — are wholly irre- 
 spective of colour, and depend only upon the state 
 or nature of the surface. Professor Powell considers 
 {Report on Rad, Heat, p. 290), after an elaborate 
 examination of all the phenomena attending the 
 heat received from the sun, that there is no simple 
 
LAWS OF HEAT. 
 
 97 
 
 radiant heat received by us from the sun's rays ; and 
 that the simple radiant heat, which no doubt is 
 initially radiated from the sun, is absorbed by the 
 atmosphere of that luminary, some small portion, 
 perhaps, which escapes, being stopped in the higher 
 regions of our own atmosphere. The experiment of 
 Sir H. Davy, on the absorption and radiation of 
 solar heat, by different colours, is not therefore 
 applicable to the case of simple heat, or such heat as 
 is given out by bodies below luminosity. 
 
 120. The Table, art. 113, evidently shows that 
 the radiation of heat, of the intensity used in those 
 experiments, bears no relation to colour. This tem- 
 perature was about 200°, and was, therefore, simple 
 heat. By this it appears, that lamp black, and white 
 paper, are equal in power, while Indian ink is much 
 less, and black lead still lower in the scale ; though, 
 as far as colour only is concerned, these last are 
 nearly the same as lamp black. But Professor 
 Powell has ascertained, {Rep. on Heat, p. 279.) that 
 the radiation and absorption of simple heat, is not 
 affected by colour, but only by the nature of the 
 surface. He found that a thermometer bulb, coated 
 with a paste of chalk, was affected even more than 
 a similar one coated with Indian ink. So, likewise, 
 Scheele found, that if two thermometers filled with 
 alcohol, one red, and the other colourless, were 
 exposed to the sun's rays, the coloured one would 
 
 H 
 
98 
 
 LAWS OF HEAT. 
 
 rise in temperature much more rapidly than the 
 other ; but if they were both plunged into the same 
 vessel of hot water, they rose equally in equal times. 
 
 121. We are fully justified, then, from these and 
 analogous experiments, in drawing the conclusion, 
 that the radiatio7i of simple heat is not influenced 
 by the colour of the heated body. Any difference 
 which appears to obtain in this respect, is, therefore, 
 solely referrible to the nature of the colouring sub- 
 stance. 
 
 122. The last of the laws of heat to which we 
 shall allude, is one which is, perhaps, more remark- 
 able than any that have been mentioned. It is that 
 which is called the capacity of bodies for calofic, or, 
 the law of specific heat. Though the principle is 
 simple, the law is intricate ; for it follows no constant 
 ratio with the density, elasticity, or other known 
 properties of matter ; though Dr. Martin considered 
 that the capacity of bodies for heat, was nearly in 
 the inverse order of their conducting powers. 
 
 123. The same quantity of heat which will raise 
 the temperature of a pound of water T, will raise 
 the temperature of a pound of oil 2°, or a pound 
 of mercury 23° ; and almost every known substance 
 possesses a capacity for caloric peculiar to itself. In 
 a subsequent chapter, a practical application of this 
 part of the laws of heat will be shown ; but to follow 
 ^t, in an extended manner, would lead to investiga- 
 
LAWS OF HEAT. 
 
 99 
 
 tions not connected with the subject of this treatise, 
 and only such of the laws of heat as are applicable 
 to this inquiry, were purposed to be here inves- 
 tigated. 
 
 H 2 
 
CHAPTER VIL 
 
 Experiments on Cooling. 
 
 J 24. From what has been stated in the preceding 
 chapter, it is evident, that the velocity with which a 
 heated body cools, depends upon various circum- 
 stances ; and experiments are necessary, in order to 
 obtain data for the calculations, which the known 
 laws of heat enable us afterwards to make. 
 
 125. No experiments on cooling are extant, that 
 appear to be suitable to the present purpose, ex- 
 cept some that were made by Tredgold, and these 
 are extremely erroneous in the application he has 
 made of them. For he has neglected all considera- 
 tions of the thickness of the body on which he 
 experimented, and has therefore estimated, that the 
 rate of cooling of a thin sheet-iron vessel, containing 
 a heated fluid, is the same only as it would be, were 
 it of any greater thickness. The same error also 
 occurs in his experiments on the cooling of glass; 
 and, consequently, all his conclusions on the disper- 
 
ON COOLING. 
 
 101 
 
 sion of heat, are entirely incorrect. Another source 
 of error lies in his having estimated the quantity of 
 water which the vessels contained, at too large an 
 amount, in order to allow for the specific heat of the 
 vessel. Had the total quantity of heat that the 
 vessel contained, been the object sought, this mode 
 of calculation would have been correct ; but it is 
 not so, when the rate of cooling only, is the element 
 required. The effect of each of these errors, is to 
 make the rate of dispersion appear to be more rapid 
 than the true velocity; and the result is, that in 
 some of his experiments the errors amount to 
 upwards of 16 per cent. 
 
 126. To ascertain by experiment the velocity of 
 cooling, for a surface of cast-iron, I used a pipe 30 
 inches long, 2^ inches diameter internally, and 3 
 inches diameter externally: the ends were closed, 
 and the bulb of a thermometer was inserted about 
 3 inches into the water at one end, the tempera- 
 ture being alike in every part of the pipe. The 
 exposed surface of the pipe was 287*244 square 
 inches, and the quantity of water contained in it 
 was 171*875 cubic inches. The rates of cooling 
 were tried with different states of the surface : first, 
 when it was in the usual state of cast-iron pipes, 
 covered with the brown surface of protoxide of iron; 
 next it was varnished black ; and finally, the varnish 
 was scraped off, and the pipe was painted white with 
 two coats of lead paint. The following Table shows 
 
102 
 
 EXPERIMENTS 
 
 the observed time of cooling, corrected and reduced 
 to the same excess of temperature above the circum- 
 ambient air. 
 
 TABLE of the Cooling of Iron. 
 
 Temperature of Room 67°. Maximum Temperature of 
 Thermometer 152°. 
 
 Thermometer 
 
 
 
 Black varnished 
 
 
 
 cooled, 
 
 Rusty Surface. 
 
 Surface. 
 
 Vvhite Surface. 
 
 
 
 Observed 
 
 Calcu- 
 
 Observed 
 
 Calcu- 
 
 Observed 
 
 Calcu- 
 
 from 
 
 to 
 
 Time. 
 
 lated 
 
 Time. 
 
 lated 
 
 Time. 
 
 lated 
 
 
 
 
 Time. 
 
 
 Time. 
 
 
 Time. 
 
 152° 
 
 150° 
 
 2' 30'' 
 
 2' 21'' 
 
 2' 16" 
 
 2' 16" 
 
 2' 19" 
 
 2' 24" 
 
 152 
 
 148 
 
 5 
 
 4 44 
 
 4 38 
 
 4 36 
 
 4 53 
 
 4 51 
 
 152 
 
 146 
 
 7 45 
 
 7 12 
 
 7 28 
 
 7 3 
 
 7 28 
 
 7 22 
 
 152 
 
 144 
 
 10 15 
 
 9 44 
 
 9 45 
 
 9 27 
 
 10 13 
 
 9 57 
 
 152 
 
 142 
 
 12 45 
 
 12 15 
 
 12 2 
 
 11 54 
 
 12 57 
 
 12 36 
 
 152 
 
 140 
 
 15 
 
 15 
 
 14 32 
 
 14 32 
 
 15 22 
 
 15 22 
 
 Minutes. 
 
 The ratios of f Black Varnished Surface . . 1*21 
 
 Cooling 1° are <^ Iron Surface 1*25 
 
 therefore, ^ White Painted Surface . . . 1*28^ 
 
 These ratios are in the proportion of 100, 103*3, 
 and 105*7; but as the relative heating effect, is the 
 inverse of the time of cooling, we shall find that 100 
 feet of varnished pipe, 103^ feet of plain iron pipe, 
 or 105f feet of iron pipe painted white, will each 
 produce an equal effect. 
 
 ' These ratios of cooling, it will be observed, are for pipes of 
 3 inches diameter : but the cooling of any other size can be cal- 
 culated from the data here given. 
 
ON COOLING. 103 
 
 127. Ill these experiments, it might have been 
 expected to find greater differences between the 
 effects of the various states of the surface, than 
 appears really to obtain. The greatest difference 
 only amounts to about 5^ per cent., but it would 
 probably be greater in proportion, with an increased 
 thickness of the coating of paint. 
 
 128. To ascertain the effect of glass windows in 
 cooling the air of a room, the following experiments 
 were made, with a vessel as nearly as possible 
 of the same thickness as ordinary window glass. 
 The temperature of the room, in these experiments, 
 was 65° ; the thickness of the glass was "0825 of an 
 inch ; the surface of the vessel measured 34*296 
 square inches, and it contained 9*794 cubic inches 
 of water. The time in which this vessel cooled, 
 when filled with hot water, is shown as follows : 
 
 TABLE of the Cooling of Glass. 
 
 Thermometer cooled, 
 
 Observed 
 
 Time 
 of Cooling. 
 
 Calculated 
 
 Time 
 of Cooling. 
 
 Average Rate 
 
 of the 
 Observed Time 
 of Cooling. 
 
 from 
 
 to 
 
 150° 
 150 
 150 
 150 
 
 140° 
 130 
 120 
 110 
 
 6' 40'' 
 14 15 
 23 30 
 34 
 
 6' 54" 
 14 43 
 23 40 
 34 
 
 1 
 
 ^1-176° per mi- 
 nute, at an ex- 
 cess of 65° 
 above the Tem- 
 perature of the 
 
 [ Air. 
 
 129. From the average rate of cooling which is 
 here given, the effect of glass in cooling the air of a 
 
104 
 
 EXPERIMENTS 
 
 room may easily be calculated. As the specific heat 
 of equal volumes of air and water \ is as 1 to 2990, 
 the above average will show that each square foot 
 of glass will cool 1*279 cubic feet of air T per 
 minute, when the temperature of the glass is V 
 above that of the external air. 
 
 130. But by this we shall only find the effect 
 of glass in a still atmosphere ; and, therefore, to as- 
 certain the cooling effect of external windows, when 
 exposed to the action of winds, farther experiments 
 are necessary. 
 
 131. In some researches of Leslie's, on the 
 cooling power of wind, he used a bright metallic 
 ball filled with hot water, and noted the time of 
 cooling when it was exposed to wind at different 
 velocities. The result he obtained was, that the 
 cooling effect on the ball was very nearly in a direct 
 ratio with the velocity. But it will be obvious, by 
 referring to the experiments of Petit and Dulong, 
 in the preceding chapter, that the relative cooling of 
 heated bodies, when exposed to air moving at 
 different velocities, must depend upon the nature of 
 the surfaces. For while the quantity of heat which 
 is abducted by the air, is proportional to the number 
 of particles of air which pass over the heated body 
 in a given time, the heat that is lost by radiation is 
 not only independent of this effect, but the relative 
 
 See Art. 139. 
 
ON COOLING. 
 
 105 
 
 proportion of beat lost by radiation, differs for each 
 particular substance. As the bright metal ball that 
 Leslie employed in his experiments, would lose only 
 an extremely small proportion of its heat by radia- 
 tion, it might naturally be concluded that the rate 
 of cooling would be nearly in a direct ratio with the 
 velocity of the air. But with a surface of glass, the 
 result must be very different, because the radiation 
 is then very considerable ; and, therefore, the total 
 cooling will be much slower than the simple ratio of 
 the velocity. For while a surface of glass of the 
 temperature of 120°, and at an excess of 52° above 
 the surrounding medium, loses about two-thirds of 
 its heat by radiation, a bright metallic surface, of the 
 same temperature, will only lose one-eleventh part 
 of its heat by the same cause. 
 
 132. In the following experiments it appears 
 that the cooling effect of wind, at different velocities, 
 on a thin surface of glass, is very nearly as the 
 square root of the velocity. In these experiments, 
 the velocity of the air was measured by the revolu- 
 tion of the vanes of a fan ; the temperature of the 
 air was 68° ; the time required to cool the thermo- 
 meter 20° was noted for every different velocity, 
 and the maximum temperature of the thermometer, 
 in each experiment, was 120°. In still air it re- 
 quired 5' 45^' to cool the thermometer this extent ; 
 and the following table shows the time of cooling 
 by air in motion. 
 
106 EXPERIMENTS 
 
 TABLE of the Cooling of Glass by Wind. 
 
 Velocity 
 of the Wind, 
 in Miles, 
 per hour. 
 
 Times of CooUng the Thermometer 20°. 
 From 120° to 100° of Fahrenheit. 
 
 Observed 
 
 Time 
 of CooHng. 
 
 Time, 
 reduced to 
 decimals of a 
 minute. 
 
 Corrected Time ; being 
 the Inverse of the 
 Square Root of the 
 
 Velocities ; in decimals 
 of a minute. 
 
 3-26 
 5-18 
 6'54 
 8-86 
 10-90 
 13-36 
 17-97 
 20-45 
 24-54 
 27-27 
 
 2' 35" 
 2 10 
 1 55 
 1 40 
 1 30 
 1 15 
 1 5 
 1 
 55 
 48 
 
 2-58 
 2-16 
 1-91 
 1-66 
 1-50 
 1-25 
 1-08 
 1-0 
 -91 
 •81 
 
 2-58 
 2-04 
 1-82 
 1-56 
 1-41 
 1-27 
 1-10 
 1-03 
 •94 
 -88 
 
 133. In consequence of the large quantity of 
 glass in buildings used for horticultural purposes, 
 the cooling effect of wind is of considerable import- 
 ance. We see, however, that with an increased 
 velocity, the cooling effect is considerably less in 
 proportion, on glass than on metal : and it will 
 be very much less on window-glass than even what 
 is here stated ; for, as glass is an extremely bad 
 conductor of heat, the increased thickness which 
 windows-glass possesses over that which composes 
 the bulb of a thermometer, will make a material 
 difference in the quantity of heat that is lost by the 
 abduction of the air, as there will be, in this case, a 
 greater difference between the temperature of the 
 
ON COOLING. 
 
 107 
 
 external and the internal surface. The cooling 
 effect of wind is therefore not near so considerable 
 on glass as is generally supposed ; and it will pro- 
 bably be nearly one-half less on window-glass than 
 what is shown by the preceding experiments. 
 
CHAPTER VIII. 
 
 Heat by Combustion — Quantity of Heat from Coal — Specific 
 Heat of Air and Water — Measure of Effect for Heated Iron 
 Pipe — Cooling Power of Glass — Quantity of Pipe required 
 to warm a given space — Quantity of Coal consumed — 
 Time required to heat a Building — Facile Method of Cal- 
 culating the Quantity of Pipe required in any Building. 
 
 134. Having in the preceding chapters investigated 
 some of the fundamental laws of heat, we proceed 
 to consider the particular effects practically dedu- 
 cible from them, so far as they relate to the subject 
 of the present inquiry. 
 
 135. Very erroneous notions are entertained by 
 many persons, as to the absolute quantity of heat 
 contained in different substances. This subject has 
 already been mentioned ; and, in the present chapter 
 we shall have occasion to apply this law of specific 
 heat in several calculations. 
 
 136. Of the effect produced by the decompo- 
 sition of combustible materials by fire, it may 
 also be observed that erroneous notions prevail : for 
 
HEAT FROM COALS. 
 
 109 
 
 the quantity of heat obtainable by the combustion 
 of any substance, is not, as many persons appear to 
 consider, illimitable, but is as fixed and determinate 
 as any other of the laws of heat. The amount of it 
 depends on the chemical composition of the parti- 
 cular substance ; but this, however, is quite inde- 
 pendent of any difference which obtains in the 
 effect, in consequence of the perfection or imperfec- 
 tion of the apparatus in which the combustion is 
 performed. 
 
 137. Though every kind of fuel differs in the 
 quantity of heat that it affords, it is unnecessary, 
 in such an inquiry as this, to regard any other than 
 the ordinary description used for purposes similar 
 to that we are now considering. The calculations 
 will therefore be made only with reference to New- 
 castle coal of a good average quality. 
 
 138. It is stated by Watt, that 1 lb. of coal will 
 raise the temperature of 45 lbs. of water from 55° 
 to 212°. Rumford states the same quantity of coal 
 will raise 36^2^ lbs. of water from 32° to 212°; and 
 Dr. Black has estimated that 1 lb. weight of coal 
 will make 48 lbs. of water boil, supposing it pre- 
 viously to be at a mean temperature. These quan- 
 tities, when reduced to a common standard, vary 
 but little from each other. Watt's experiment of 
 45 lbs. of water being heated from 55° to 212°, is 
 equal to 39^: lbs. only, if heated from 32° to 212° : 
 and this nearly agrees with Count Rumford's calcu- 
 
110 
 
 SPECIFIC HEAT 
 
 lation ; at least the variation is not more than might 
 be expected from a slight difference in the quality 
 of the coal. Dr. Black's estimate is as much in 
 excess, over the experiment of Watt, as Rumford's 
 is in defect: we may, therefore, take the average 
 of these three experiments, which will give as a 
 result, that 39 lbs. of water may be heated from 
 32° to 2 12° by 1 lb. of coal. 
 
 139. To ascertain the effect which a certain quan- 
 tity of hot water will produce, in warming the air 
 of a room, there appears to be no better method 
 than that of computing from the specific heat of 
 gases compared with water. 
 
 140. Every substance, it has before been ob- 
 served, has its peculiar specific heat. Now, 1 cubic 
 foot of water by losing T of its heat, will raise the 
 temperature of 2990 cubic feet of air\ the like 
 extent of 1° : and by losing 10° of its heat, it will 
 
 1 The specific heat of eqval weights of water and air, by the 
 experiments of Berard and Delaroche, is found to be as 1 to '26669: 
 but as the volume, or bulk, of an equal weight of atmo- 
 spheric air is to water, as 827*437 to 1, we shall have '26669 : 
 1 :: 827*437 = 3102, which is the number of cubic feet of air 
 that has the same specific heat as 1 cubic foot of water. This, 
 however, appears to be rather too high a calculation : for Dr. 
 Apjohn, in a memoir recently published {Rep. Brit. Sci. Assoc. 
 vol. iv.) gives the result of a new and accurate mode of deter- 
 mining the specific heat of permanently elastic fluids, by which 
 he makes the specific heat of atmospheric air '2767, when that of 
 water is represented by unity. Therefore '2767 : 1 !*. 827*437 
 = 2990, which is the number given in the text. 
 
OF AIR AND WATER. 
 
 Ill 
 
 raise the temperature of 2990 cubic feet of air 10°, 
 or 29,900 cubic feet 1°, and so on. 
 
 J 41. In order to know the time it will take to 
 heat a certain quantity of air, any required number 
 of degrees, by means of hot water contained in me- 
 tal pipes, we must calculate the effect from direct 
 experiment ; and, as the radiating and conducting 
 powers of different substances vary considerably, it 
 is necessary that the experiment be made with the 
 same material as the pipes for which we wish to 
 estimate the effect. 
 
 142. From the data obtained by experiments on 
 the cooling of iron pipes', it appears that the water 
 contained in a pipe 4 inches diameter, loses '851 of 
 a degree of heat per minute, when the excess of its 
 temperature is 125° above that of the circumambient 
 air. Therefore (by Art. 140), 1 foot in length, of 
 pipe, 4 inches diameter, will heat 222 cubic feet of 
 air 1° per minute, when the difference between the 
 temperature of the pipe and the air is 125°. 
 
 143. To calculate the quantity of pipe that will 
 be necessary to warm any particular room or build- 
 ing, and to maintain it at the required temperature, 
 the heat lost by the necessary ventilation, and by 
 the conducting and radiating power of the glass, 
 and of any metallic substances used in the building, 
 must be estimated. 
 
 144. The calculations of the quantity of air re- 
 ^ See Experiments on Cooling, Art. 126. 
 
112 
 
 LOSS OF HEAT 
 
 quired for ventilation, and the method of ventilating 
 buildings, are considered in a subsequent chapter. 
 (Chapter XI.) It is unnecessary, therefore, in this 
 place to pursue the subject further than to state, 
 that, in all public buildings, and rooms of dwelling- 
 houses, a quantity of air equal to 3^ cubic feet 
 for each individual the room contains, must be 
 changed per minute, in order to preserve the whole- 
 someness and purity of the atmosphere. 
 
 145. The loss of heat in all buildings having any 
 great extent of glass, we shall find to be very consi- 
 derable. It appears by experiment^ that 1 square 
 foot of glass will cool 1*279 cubic feet of air, as 
 many degrees per minute, as the internal tempera- 
 ture of the room exceeds the temperature of the 
 external air : that is, if the difference between the 
 internal and the external temperature of the room 
 be 30°, then 1*279 cubic feet of air will be cooled 
 30" by each square foot of glass, or, more correctly, 
 as much heat as is equal to this, will be given off 
 by each square foot of glass ; for, in reality, a very 
 much larger quantity of air will be affected by the 
 glass, but it will be cooled to a less extent. The 
 real loss of heat from the room will therefore be 
 what is here stated. 
 
 146. But though this effect is only in a still atmos- 
 phere, as intense cold is seldom or never accom- 
 
 ' Experiments on Cooling, Art. 129. 
 
IN BUILDINGS. 
 
 113 
 
 panied with high winds \ no additional allowance 
 needs be made for this cause, provided we calculate 
 sufficiently low for the external temperature. For 
 the highest winds are generally about March and 
 September: and the average temperature of the 
 former month is 46°, and the latter 59|-°. The 
 greatest diurnal variation of the thermometer is 20° 
 in March, and 18° in September, so that the average 
 temperature of the nights will be 36° in March^ 
 and 50° in September. But we shall find (Art. 
 152), that when the external atmosphere is at 36°, 
 the quantity of pipe required to warm a building to 
 65°, is only about one-half of what would be necessary 
 were the external air at 10° : therefore, if we cal- 
 culate that the external temperature will be 10°, 
 when we estimate the quantity of pipe required to 
 warm a building which is to be used during the 
 night, and that it will be 25° or 26°, externally, in 
 the case of such buildings as are only wanted to 
 
 ^ That intense cold is rarely accompanied by high winds, is 
 matter of common experience. The obliquity of the sun's rays 
 on the higher latitudes of the Northern hemisphere, when near 
 the time of the winter solstice, prevents the atmosphere of those 
 places which are distant from the Tropics from receiving any 
 considerable quantity of heat ; and, therefore, the air being all of 
 nearly equal density, there is but little tendency to aerial currents 
 in the lower strata. 
 
 ^ These temperatures are for the neighbourhood of London. 
 In March, 1837, the night temperature, obtained by a register 
 thermometer, only averaged 31*1°, which is nearly 5° lower than 
 has been known for many years. 
 
 I 
 
114 
 
 LOSS OF HEAT 
 
 be warmed during the day, the required heat can 
 then be maintained, even during the time of high 
 winds 
 
 147. But in such situations as are very much 
 exposed to high winds, it will be prudent to calcu- 
 late the external temperature from zero, or even 
 below that, according to circumstances; and, in 
 very warm and sheltered situations, a less range in 
 the temperature will be sufficient: a local know- 
 ledge of the situation will therefore be necessary to 
 guide the judgment in particular cases. 
 
 148. The difference between the cooling effect of 
 glass which is glazed in squares, and that which is 
 lapped, is very trifling in those buildings where the 
 air contains much moisture. This is the case in hot- 
 houses, where the plants are constantly steamed, and 
 therefore, for such buildings, no farther allowance 
 should be made on this account, for loss of heat^ 
 
 ^ By reckoning the external air at the above temperatures, the 
 wind may have a velocity of from 20 to 30 miles an hour, without 
 producing any diminution of the internal temperature ; for it is 
 probable that the cooling effect of wind on window glass, is not 
 above one half as much as appears by the experiments. Art. 132. 
 
 ^ The calculations of the specific heat of air, given in the note, 
 Art. 140, are only for dry air. If the temperature be at 60°, and 
 the air saturated with moisture, then the same quantity of heat 
 will only raise the temperature of 2967 cubic feet of this saturated 
 air any given number of degrees, which would have raised 2990 
 cubic feet of dry air to the like temperature. This 2967 cubic 
 feet of saturated air will contain 67 cubic inches of water ; and 
 this quantity of water will absorb as much heat during its conver- 
 sion into vapour, as would raise the temperature of 115,922 cubic 
 
 12 
 
IN BUILDINGS. 
 
 115 
 
 But in skylights of dwelling-houses, in consequence 
 of the greater dryness of the atmosphere, the heated 
 air will escape through the laps of the glass in 
 greater quantity, in proportion as less vapour is con- 
 densed on the surface. The height of the skylight 
 will also make a considerable difference in the 
 velocity of the escape of air through the laps, as it 
 depends upon the same principles which have been 
 explained (Art. 33), as governing the motion of 
 water ; the increased velocity being relatively as 
 the height and the difference of temperature be- 
 tween the internal and external air. 
 
 149. In making an estimate of the quantity of 
 glass contained in any particular building, the extent 
 of surface of the wood work must be carefully ex- 
 cluded from the calculation. This is particularly 
 necessary in buildings used for horticultural pur- 
 poses, where, from the smallness of the panes, the 
 wood-work occupies a considerable space. The 
 readiest way of calculating, and sufficiently accurate 
 for ordinary purposes, is to take the square surface 
 
 feet of air 1°. This is equal to the entire heat that 46 feet of 
 pipe, 4 inches diameter, will give off in ten minutes, when its 
 temperature is 140° above that of the air. The glass will, how- 
 ever, cool much less of this saturated air, than of dry air, for the 
 mixture of air and vapour has greater specific heat than dry air. 
 With lapped glass the loss of heat will be less with saturated than 
 with dry air, because the vapour when condensed upon the glass, 
 will run down and nearly fill up the crevices between the laps, 
 and effectually prevent the escape of the air, and thereby avoid 
 the loss of heat. 
 
 I 2 
 
116 
 
 QUANTITY OF PIPE 
 
 of the sashes, and then deduct one-eighth of the 
 amount for the wood-work. In the generality of 
 horticultural buildings, the wood-work fully amounts 
 to this quantity : but in some expensively finished 
 conservatories, &c., it is considerably less, and there- 
 fore the allowance must be made accordingly. When 
 the frames and sashes are made of metal, the radia- 
 tion of heat will be quite as much, from the frame 
 as from the glass ; therefore, in such cases, no deduc- 
 tion must be made. 
 
 150. Some loss of heat will likewise arise from 
 imperfect fitting of doors and windows. In these 
 cases the circumstances vary very considerably ; but 
 in the majority of instances, no allowance is neces- 
 sary for these sources of loss of heat, the external 
 temperature of the air having been reckoned suffi- 
 ciently low to supersede the necessity of any farther 
 deduction. 
 
 151. From the preceding calculations, the follow- 
 ing corollary may be drawn : — the quantity of air 
 to be warmed "per minute, in habitable rooms and 
 public buildings, must be 3^ cubic feet for each 
 person the room contains, and 1^ cubic feet for each 
 square foot of glass ; and for conservatories, forcing 
 houses, and other buildings of this description, the 
 quantity of air to be warmed jter minute, must be 
 \\ cubic feet for each square foot of glass which the 
 building contains. When the quantity of air re- 
 quired to be heated, has been thus ascertained, the 
 
FOR WARMING BUILDINGS. 
 
 117 
 
 length of pipe which will be necessary, may be found 
 by the following 
 
 Rule: — Multiply 125 by the difference between 
 the temperature at which the room is purposed to 
 be kept, when at its maximum, and the temperature 
 of the external air ; and divide this product by the 
 difference between the temperature of the pipes, and 
 the proposed temperature of the room : then, the 
 quotient thus obtained, when multiplied by the num- 
 ber of cubic feet of air to be warmed per minute, and 
 this product divided by 222, will give the number of 
 feet in length, of pipe 4 inches diameter, which will 
 produce the desired effect.^ 
 
 When the pipes which are to be used, are 3 
 inches diameter, then the number of feet of 4-inch 
 pipe, obtained by this rule, must be multiplied by 
 1*33, which will give the length of 3-inch pipe : or 
 to obtain the quantity of 2-inch pipe, the length of 
 
 ' Let p be the temperature of the pipe, and t the temperature 
 
 125 
 
 the room" is required to be kept at ; then = ^c, which will 
 
 represent the number of feet of pipe that will warm 222 cubic 
 feet of air 1° per minute, when p — t is different to the proportions 
 given in art. 142. If d represents the difference between the 
 internal and the external temperature of the room, and c the 
 number of cubic feet of air which are to be warmed per minute, 
 d.c 
 
 then X . = F, will be the number of feet of pipe 4 inches 
 
 diameter, which will warm any quantity of air per minute, 
 according to the calculations art. 142. 
 
 The rule given in the text has been arranged in such a man- 
 ner, that it may be worked without decimals. 
 
118 
 
 QUANTITY OF PIPE 
 
 pipe 4 inches diameter, obtained by the rule, must 
 be multiplied by 2 ; the length required of 3-inch 
 pipe, being one-third more than 4-inch, and the 
 length of 2-inch pipe being double that of the 
 4-inch, when the temperatures are the same in all. 
 
 152. By the following table, however, even the 
 simple calculations given in this rule may be dis- 
 pensed with. The table shows the quantity of pipe 
 4 inches diameter, which is required to heat 1000 
 cubic feet of air jier minute^ any number of degrees. 
 The temperature of the pipes is assumed to be 200"" 
 of Fahrenheit ; this being the most usual tempera- 
 ture at which they can be easily maintained. But 
 according to the length of pipe which is heated by 
 one boiler, the temperature will sometimes be greater 
 and sometimes less than this estimate, the tempera- 
 ture of the water being generally higher when only 
 a small quantity of pipe is used. When the quantity 
 of air to be warmed 'per minute is greater or less 
 than 1000 cubic feet, the proper quantity of pipe 
 will be found, by multiplying the length given in the 
 table, by the number of cubic feet of air to be 
 warmed per minute^ and dividing that product by 
 1000. 
 
FOR WARMING BUILDINGS. 
 
 119 
 
 TABLE of the Quantity of Pipe, 4 inches diameter, which will heat 
 1000 Cubic Feet of Air per minute, any required Number of 
 Degrees : the Temperature of the Pipe being 200° Fahrenheit. 
 
 Temperature 
 of external 
 
 Temperature at which the room is 
 
 required to t 
 
 e kept. 
 
 Fahrenheit's 
 Scale. 
 
 45° 
 
 50° 
 
 55° 
 
 60° 
 
 65° 
 
 70° 
 
 75" 
 
 80° 
 
 85° 
 
 90° 
 
 10° 
 
 126 
 
 150 
 
 174 
 
 200 
 
 229 
 
 259 
 
 292 
 
 328 
 
 367 
 
 409 
 
 12° 
 
 119 
 
 142 
 
 166 
 
 192 
 
 220 
 
 251 
 
 283 
 
 318 
 
 357 
 
 399 
 
 14° 
 
 112 
 
 135 
 
 159 
 
 184 
 
 212 
 
 242 
 
 274 
 
 309 
 
 347 
 
 388 
 
 16^ 
 
 105 
 
 127 
 
 151 
 
 176 
 
 204 
 
 233 
 
 265 
 
 300 
 
 337 
 
 378 
 
 18° 
 
 98 
 
 120 
 
 143 
 
 168 
 
 195 
 
 225 
 
 256 
 
 290 
 
 328 
 
 368 
 
 20° 
 
 91 
 
 112 
 
 135 
 
 160 
 
 187 
 
 216 
 
 247 
 
 28] 
 
 318 
 
 358 
 
 22° 
 
 83 
 
 105 
 
 128 
 
 152 
 
 179 
 
 207 
 
 238 
 
 271 
 
 308 
 
 347 
 
 24° 
 
 76 
 
 97 
 
 120 
 
 144 
 
 170 
 
 199 
 
 229 
 
 262 
 
 298 
 
 337 
 
 26° 
 
 69 
 
 90 
 
 112 
 
 136 
 
 162 
 
 190 
 
 220 
 
 253 
 
 288 
 
 327 
 
 28° 
 
 61 
 
 82 
 
 104 
 
 128 
 
 154 
 
 181 
 
 211 
 
 243 
 
 279 
 
 317 
 
 30° 
 
 54 
 
 75 
 
 97 
 
 120 
 
 145 
 
 173 
 
 202 
 
 234 
 
 269 
 
 307 
 
 Freezing? q.^O 
 point 5 
 
 4 7 
 
 67 
 
 89 
 
 112 
 
 137 
 
 164 
 
 193 
 
 225 
 
 259 
 
 296 
 
 34° 
 
 40 
 
 60 
 
 81 
 
 104 
 
 129 
 
 155 
 
 184 
 
 215 
 
 249 
 
 286 
 
 36° 
 
 32 
 
 52 
 
 73 
 
 96 
 
 120 
 
 147 
 
 175 
 
 206 
 
 239 
 
 276 
 
 38° 
 
 25 
 
 45 
 
 66 
 
 88 
 
 112 
 
 138 
 
 166 
 
 196 
 
 230 
 
 266 
 
 40° 
 
 18 
 
 37 
 
 58 
 
 80 
 
 104 
 
 129 
 
 157 
 
 187 
 
 220 
 
 255 
 
 42° 
 
 10 
 
 30 
 
 50 
 
 72 
 
 95 
 
 121 
 
 148 
 
 178 
 
 210 
 
 245 
 
 44° 
 
 3 
 
 22 
 
 42 
 
 64 
 
 87 
 
 112 
 
 139 
 
 168 
 
 200 
 
 235 
 
 46° 
 
 
 15 
 
 34 
 
 56 
 
 79 
 
 103 
 
 130 
 
 159 
 
 190 
 
 225 
 
 48° 
 
 
 7 
 
 27 
 
 48 
 
 70 
 
 95 
 
 121 
 
 150 
 
 181 
 
 214 
 
 50° 
 
 
 
 19 
 
 40 
 
 62 
 
 86 
 
 112 
 
 140 
 
 171 
 
 204 
 
 52° 
 
 
 
 11 
 
 32 
 
 54 
 
 77 
 
 103 
 
 131 
 
 161 
 
 194 
 
 To ascertain by the above 4;able, the quantity of pipe which 
 will heat 1000 cubic feet of air per minute ; — find, in the first 
 column, the temperature corresponding to that of the external 
 air, and in one of the other columns find the temperature of the 
 room : then, in this latter column, and on the line which corres- 
 ponds with the external temperature, the required number of feet 
 of pipe will be found. 
 
 153. If tbe buildiDOf which it is clesiD:ned to 
 warm, is required to be used only during the day, 
 the air, in this part of the country at least, is 
 
120 
 
 QUANTITY OF COAL 
 
 scarcely likely to be below 25° ; but if, — as for a 
 forcing-house, for instance, — it is required to be 
 warmed both day and night, then, perhaps, 1 0° will 
 not be too low to calculate from, or 22° below freez- 
 ing. Suppose, now, a forcing-house has to be kept 
 at 75° in the coldest weather, — which we will sup- 
 pose to be 10° of Fahrenheit, — then by the Table 
 we find, under the column 75°, and on the line with 
 10° for external temperature, the quantity 292, 
 which is the number of feet in length, of pipe 4 
 inches diameter, that are required to heat 1000 cubic 
 feet of air per minute, the proposed number of 
 degrees. Any other difference of temperature may 
 be found in the same way. 
 
 154. The quantity of coal necessary to supply 
 any determinate length of pipe, is easily ascertained 
 from the data given in Art. 138. After the water 
 in the pipes is heated to its maximum, the quantity 
 of coal consumed is, obviously, just what is required 
 to supply the heat given off from the pipes. Now, 
 by Art. 126 we find, that when pipes, four inches 
 diameter, are 1 46*8° hotter than the air of the room, 
 the water contained in them loses exactly 1° per 
 minute of its heat. By Art. 138 we find that lib. 
 of coal will raise the temperature of 39 lbs. of water 
 180°; therefore, as 100 feet in length of 4-inch 
 pipe contains exactly 544 lbs. of water, it will require 
 13*9 lbs. of coal to raise the temperature of this 
 quantity of water 180°. If, therefore, the water 
 loses r of heat per minute, or 60° per hour, this 
 
FOR WARMING BUILDINGS. 
 
 121 
 
 quantity of coal will supply 100 feet in length of 
 pipe, for three hours, if its temperature continues 
 constant with regard to the air of the room. On 
 this principle the following Table has been con- 
 structed. The temperature of the pipe is assumed 
 to be 200° : then, knowing the temperature of the 
 room, if we take the difference between the tem- 
 perature of the pipe and that of the room, — by 
 looking in the Table for the corresponding tempera- 
 ture, we shall find under it the number of pounds 
 weight of coal which will be required per hour, 
 for every 100 feet in length of pipe, in order to 
 maintain the stated temperature. Thus, suppose 
 the pipe to be 4 inches diameter, and its tempera- 
 ture 200°, while the room is at 75° ; then, under the 
 column headed 125°, (which is the difference be- 
 tween these two temperatures), we find 3*9 lbs. as 
 the quantity required per hour for every 100 feet of 
 pipCc The quantities stated in the Table are given 
 in pounds and tenths of a pound. 
 
 TABLE of the Quantity of Coal used per Hour, to heat 100 
 Feet in length of Pipe of different Sizes. 
 
 Diameter 
 of 
 Pipe, 
 
 Difference between the Temperature of the Pipe and the Room, 
 in Degrees of Fahrenheit. 
 
 in Inches. 
 
 150 
 
 145 
 
 140 
 
 135 
 
 130 
 
 125 
 
 120 
 
 115 
 
 110 
 
 105 
 
 100 
 
 95 
 
 90 
 
 85 
 
 80 
 
 4 
 
 4-7 
 
 45 
 
 44 
 
 42 
 
 41 
 
 3-9 
 
 3-7 
 
 36 
 
 3-4 
 
 3-2 
 
 31 
 
 2-9 
 
 2-8 
 
 2-6 
 
 2-5 
 
 3 
 
 3-5 
 
 3-4 
 
 33 
 
 31 
 
 30 
 
 29 
 
 2-8 
 
 2-7 
 
 2-5 
 
 2-4 
 
 2-3 
 
 2-2 
 
 21 
 
 20 
 
 1-8 
 
 2 
 
 23 
 
 2-2 
 
 2-2 
 
 21 
 
 20 
 
 19 
 
 1-8 
 
 1-8 
 
 1-7 
 
 16 
 
 1-5 
 
 1-4 
 
 1-4 
 
 1-3 
 
 1-2 
 
 1 
 
 11 
 
 
 M 
 
 10 
 
 10 
 
 •9 
 
 •9 
 
 •9 
 
 •8 
 
 ■8 
 
 •7 
 
 •7 
 
 •7 
 
 •6 
 
 •6 
 
122 
 
 TIME REQUIRED 
 
 155. It should be here observed, that an appa- 
 ratus will not always consume the same quantity of 
 coal : in fact, it will but seldom require so much as 
 the Table shows, because that is the calculation for 
 the maximum effect. Suppose the quantity of pipe 
 in a room has been accurately calculated, in order 
 to maintain the temperature at 75° when the ex- 
 ternal air is at 30° ; the consumption of coal, for pipes 
 of 4 inches diameter, will then be 3*9 lbs. per hour 
 for every 100 feet of pipe. But should the external 
 temperature now rise to 40°, 77 feet of pipe would 
 produce the same effect as 100 feet would in the 
 former case : therefore, the pipe must be heated to 
 a lower temperature, and only 3 lbs. of coal would 
 be used, instead of 3*9 lbs. As much coal, there- 
 fore, as would supply 77 feet of pipe at the maxi- 
 mum temperature, would suffice for 100 feet at this 
 reduced temperature. The quantity of fuel which 
 is consumed will, therefore, be continually subject to 
 variation, as it will alter with the temperature of the 
 external atmosphere : and in general, the average 
 quantity of coal required, will be about one-third 
 less than the amount given in the Table. 
 
 156. It may not be amiss to estimate the length 
 of time which will be necessary to heat a building 
 with pipes of different sizes. This will, of course, 
 depend upon many circumstances : nevertheless, an 
 approximation may be made to the average time 
 required. Suppose the pipe is to be heated to the 
 
FOR WARMING BUILDINGS 
 
 123 
 
 temperature of 200°, the water being at 40° before 
 lighting the fire ; then the maximum temperature 
 of the building will be attained with 
 
 4-inch Pipes, in about 4j hours 
 3-inch Pipes, in about 3j hours 
 2-inch Pipes, in about 2^ hours. 
 
 But if a larger quantity of coal than that given by 
 the Table be used ; if the surface of the boiler be 
 much increased in proportion to the length of pipe ; 
 if the quantity of pipe used be excessive ; or the 
 temperature of the external air is higher than the 
 estimated amount ; then, in each of these cases, 
 the time required for heating will be less. But if, 
 on the contrary, the required temperature be not 
 attained in the time given above, then, either too 
 small a quantity of pipe, too small a surface of 
 boiler, or too small a quantity of coal has been 
 used. 
 
 157. It should, however, be observed, that although 
 the mammum temperature will not be reached, at 
 an average, in less time than is above stated ; still, 
 the required temperature will very often not take 
 longer than half or two-thirds of this time, to be 
 attained : because the quantity of pipe being always 
 apportioned to meet the case of extreme cold, when 
 the external temperature is above that extreme 
 limit, the pipe, by being superabundant, will warm 
 the same space in a shorter time. 
 
124 
 
 RULE FOR CALCULATING 
 
 158. Various circumstances may, however, inter- 
 fere to diminish the effect of the apparatus ; such, 
 for instance, as damp walls, — particularly if the 
 building is new — excess of ventilation, &c. The 
 effect of damp walls in reducing the apparent power 
 of an apparatus is very considerable, in consequence 
 of the great quantity of heat which is necessary to 
 evaporate the moisture. For it will require as much 
 heat to vaporise one gallon of water from the walls 
 of a building, as would raise the temperature of 
 47,840 cubic feet of air 10°. The true power of an 
 apparatus can, therefore, never be ascertained, unless 
 the building be perfectly dry. The same cause, 
 though in a much less degree, becomes operative in 
 buildings which are only occasionally warmed ; and 
 a longer time will always be necessary to heat such 
 places, than those that are in constant use. 
 
 159. For estimating the quantity of pipe which is 
 required to warm any building, rules of a much 
 more facile character, though, at the same time, 
 much more loose and inaccurate than those which 
 have been already given, may easily be constructed ; 
 but they will answer sufficiently well in many com- 
 mon cases. Thus, in churches and very large public 
 rooms, which have only about an average number of 
 doors and windows, and moderate ventilation, by 
 taking the cubic measurement of the room, and 
 dividing the number thus obtained by 200, the 
 quotient will be the number of feet in lengthy of pipe 
 
THE QUANTITY OF PIPE. 
 
 125 
 
 4 inches diameter, which will be required to obtain a 
 temperature of about 55° to 58°. For smaller 
 rooms, dwelling-houses, &c. the cubic measurement 
 should be divided by 150, which will give the num- 
 ber of feet of 4-inch pipe. For greenhouses, con- 
 servatories, and such like buildings, where the 
 temperature is required to be kept at about 60°, 
 dividing the cubic measurement of the building by 
 30, will give the required quantity of pipe ; and for 
 forcing-houses, where it is desired to keep the tem- 
 perature at 70° to 75°, we must divide the cubic 
 measurement of the house by 20 ; but if the tem- 
 perature be required as high as 75° to 80°, then we 
 must divide by 18, to obtain the number of feet of 
 4-inch pipe. If the pipes are to be 3 inches 
 diameter, then we must add one-third to the quantity 
 thus obtained ; and if 2-inch pipes are to be used, 
 we must take double the length of 4-inch pipe. 
 
 160. The quantity of pipe estimated in this way 
 will only suit for such places as are built quite on 
 the usual plan ; but for others, — and indeed in all 
 cases where it can be done, — the method given in 
 the former part of this chapter should be employed. 
 (Art. 151 and 152.) 
 
 161. It should here be mentioned, that the cal- 
 culations for the quantity of pipe required for horti- 
 cultural buildings, have been made with regard to 
 the most economical mode of effecting the desired 
 object. Some of the most successful horticulturists. 
 
126 
 
 HEAT IN FORCING HOUSES. 
 
 however, have adopted the plan of using a much 
 stronger heat in their forcing-houses, and allowing, 
 at the same time, a much greater degree of ventila- 
 tion than usual. This plan is stated to produce a 
 finer fruitage ; but it will only be obtained at an 
 increased cost in the apparatus, and by a larger 
 expenditure of fuel. Where economy is not required, 
 it may, perhaps, be desirable to adopt this plan ; and 
 then the quantity of pipe which is used, must be 
 proportionally increased above the estimates which 
 are given in this chapter. 
 
CHAPTER IX, 
 
 Various Modifications of the Hot-water Apparatus — Kewley*s 
 Syphon Principle — The High Pressure System — Eckstein and 
 Busby's Circulator or Rotary Float, &c. 
 
 162. Under the common and generic term of "hot- 
 water apparatus," various plans have been brought 
 forward by different inventors, which, though essen- 
 tially different in some of their features from those 
 that have been already described, are, nevertheless, 
 merely modifications of the general principles that 
 have been explained. In the present chapter, some 
 of these peculiar modifications of the invention will 
 be investigated : and it will appear, that the original 
 principles of all are the same, but that other of the 
 fundamental laws of Nature are here brought into 
 action, conjointly with those that we have already 
 examined, and give rise to an apparent diversity of 
 operation. 
 
 163. The first notable invention of this sort 
 
128 
 
 SYPHON PRINCIPLE. 
 
 which shall be mentioned, is Kewley's syphon prin- 
 ciple. The sketch, fig. Fig. 20. 
 20, shows this apparatus 
 in its simplest form. 
 The boiler is open at 
 the top, and the two 
 pipes dip into the water ; 
 the pipe a descending only a very short distance 
 below the surface, and the pipe b reaching nearly to 
 the bottom of the boiler. A small flexible metal 
 pipe, a;, is attached to the highest part of the pipes. 
 To this an air pump is connected, and the air in the 
 pipes being exhausted by this means, the atmos- 
 pheric pressure forces the water up the pipes and 
 fills them completely. This avoids the necessity of 
 having a reservoir of water higher than the top of 
 the boiler; for it is well known, that the usual 
 atmospheric pressure is capable of raising a column 
 of water in a vacuum, to about 30 feet in height, 
 varying, however, with the degree of pressure shown 
 by the barometer. 
 
 164. The water in the longer pipe, B, will acquire 
 a preponderance of weight over that in the pipe A, 
 even if it be at first of an equal temperature and 
 density; because the pipe b only receives the 
 particles of hot water which rise immediately under 
 its base, while the other receives the heat from all 
 parts of the bottom as well as the sides of the 
 
THE SYPHON PRINCIPLE. 
 
 129 
 
 boiler ; the water on the top being hotter than that 
 at the bottom. But as soon as the water circulates 
 through the pipes, it parts with its heat, and the 
 whole length of the pipe b will then be colder than 
 the pipe a, and the water will descend through b 
 with greater force. 
 
 165. In consequence of the long pipe b being 
 surrounded by the hot water in the boiler, the 
 water, while descending through it, receives a small 
 portion of heat, which lessens the difference of tem- 
 perature of the two pipes, and reduces the velocity 
 of the circulation. It appears probable, therefore, 
 that additional velocity of circulation would be 
 gained by placing the descending pipe, b, outside the 
 boiler, and attaching it to the side in the same 
 manner as the return pipe in fig. 5. The principal 
 inconvenience attending this would be the difficulty 
 of stopping the ends of the two pipes, a and b, 
 which is now done by a simple contrivance of two 
 plates screwed moveably to their base. This com- 
 pletely stops the water when necessary, — the ends 
 of the pipes being turned true to the plates, to make 
 them water tight, — and by reversing the action of 
 the pump, attached to the pipe ^, the soundness of 
 the joints can then be ascertained. A leaky joint is 
 difficult of detection by any other means, as there is 
 no emission of water from it in the usual way ; and 
 as the only immediate consequence of a leaky joint 
 is the immission of air, it is not observable except 
 
 K 
 
130 
 
 THE SYPHON PRINCIPLE. 
 
 by its stopping the circulation of the water, which 
 occurs, by the air accumulating and cutting off the 
 connection of the water between the two pipes. 
 
 166. If this plan of having the return pipe placed 
 outside the boiler were found to increase the motive 
 power of the apparatus, an advantage would be 
 gained in all those cases where the pipes are required 
 to pass under a doorway ; because, in all such cases, 
 the boiler must be set much lower beneath the level 
 of the floor, in the same manner, and for the same 
 reasons, which have already been explained with 
 regard to the common hot-water apparatus. But 
 by increasing the motive power, a less height would 
 be sufficient; and it would therefore prevent the 
 inconvenience sometimes found to attend this par- 
 ticular form of the apparatus, arising from the great 
 depth the furnace is required to be sunk beneath 
 the level of the pipes, in consequence of the very 
 large size of the boiler which is generally used. 
 
 167. A singular fact is connected with this 
 invention, which deserves notice, because it arises 
 from a philosophical principle, which, in some other 
 instances, has been applied in a most useful manner ; 
 though, with this invention, it is rather disad- 
 vantageous than otherwise. It has already been 
 stated, that the height to which the water will rise 
 in a vertical column, by the atmospheric pressure, is 
 about 30 feet above the boiler. Supposing this to 
 be the extreme limit to which the water will ascend, 
 
THE SYPHON PRINCIPLE. 
 
 J31 
 
 if the pipe be elongated in the least above this, a 
 
 vacuum will be formed, similar to that at the top of 
 
 a barometer, and the water at the top of the pipe 
 
 will, in this case, be without any 'pressure. But if, 
 
 instead of 30 feet, the pipe be continued upwards 
 
 only 15 feet, then the pressure on the water, in the 
 
 upper part of the pipe, will be 1\ lbs. on the square 
 
 inch, — or half the usual atmospheric pressure ; — and 
 
 so on for other heights. Now, the boiling point of 
 
 all liquids varies with the pressure. Water boils at 
 
 212°, under the mean pressure of 15 lbs. per square 
 
 inch; but by reducing the pressure, it boils at a 
 
 lower temperature; so that, at half the mean 
 
 pressure of the atmosphere, it boils at about 186°. 
 
 Suppose now that the pipes just described, rise 30 
 
 feet above the boiler, the w^ater at the top will boil 
 
 at the temperature of 161°, and will form steam in 
 
 the upper part of the pipe ; and this, by its great 
 
 expansion, will force the water down and overflow 
 
 the boiler, or the supply cistern. For at the ordinary 
 
 pressure of the atmosphere, steam occupies about 
 
 1700 times as much space as the water from which 
 
 it is formed, and still more at a diminished pressure ; 
 
 its expansion being inversely as the pressure. When 
 
 the pipes rise to other heights above the boiler than 
 
 that described above, the boiling points will be as 
 
 follows, — 
 
 at 5 feet high, the boiling point will be 203° 
 
 10 195° 
 
 15 186° 
 
 K 2 
 
132 
 
 THE SYPHON PRINCIPLE. 
 
 20 feet high, the boiling point will be 178° 
 
 25 169° 
 
 30 161° 
 
 therefore the water in the boiler must always be 
 kept below these temperatures, according to the 
 height to which the pipes ascend \ 
 
 168. This peculiarity, which applies only to pipes 
 on the syphon principle, is more a philosophical fact 
 than a practical difficulty ; for the water can gene- 
 rally be kept at a temperature sufficiently low for 
 any ordinary height that is required. And, in fact, 
 the boiling point will generally be higher than the 
 temperatures here stated ; because a small portion 
 of air always remains in the pipes, which increases 
 the pressure on the water, and makes the boiling 
 point higher than the calculated amount. 
 
 169. This form of the apparatus answers the 
 intended purpose extremely well, and has been 
 
 ^ These calculations are made by Wollaston's rule for his 
 thermometric barometer. But this rule, although accurate at 
 moderately small differences of pressure, is undoubtedly erroneous 
 at considerable reductions of pressure. Professor Robison esti- 
 mates the boiling point of water, in vacuo, at only 88°, instead of 
 161° which Wollaston's rule shows ; and it is probable that the 
 relative proportion between the pressure and the boiling point is 
 in a logarithmic ratio, instead of the common arithmetical propor- 
 tion of Wollaston's rule. This, in fact, is found to be the case 
 at temperatures above 212°. But it is probable that, in the 
 present case, Wollaston's rule will give a more accurate result than 
 the other ; because, as the vacuum in the pipes cannot be at all 
 perfect, the boiling points will be much higher than the calculated 
 temperature ; perhaps even higher than stated in the text. 
 
THE HIGH PRESSURE SYSTEM. 
 
 133 
 
 extensively applied in practice : and it exhibits not 
 only a considerable knowledge of the principles of 
 science, but also great ingenuity in their application. 
 
 170. The next invention which we shall consider, 
 is, the High Pressure hot-water apparatus. This 
 apparatus consists of a coil of small iron pipe, built 
 into a furnace, the pipe being carried from the 
 upper part of the coil, and continued round the room 
 or building which is to be warmed, forming a con- 
 tinuous pipe when again joined to the bottom of the 
 coil. The diameter of this pipe is one inch exter- 
 nally, and half an inch internally. A large pipe, of 
 about 2-i- inches diameter, is connected, either hori- 
 zontally or vertically, with the small pipe, and is 
 placed at the highest point of the apparatus. This 
 large pipe, which is called " the expansion pipe," has 
 an opening near to its lower extremity, by which the 
 apparatus is filled with water, the aperture being 
 afterwards secured by a strong screw ; but the ex- 
 pansion pipe itself cannot be filled higher than the 
 opening just named. After the water is introduced, 
 the screws are all securely fastened, and the appa- 
 ratus becomes completely hermetically sealed. The 
 expansion pipe, which is thus left empty, is calcu- 
 lated to hold about -~ as much water as the whole 
 of the small pipes ; this being necessary in order to 
 allow for the expansion that takes place in the 
 volume of the water when heated, and which, other- 
 wise, would inevitably burst the pipes, however 
 
134 
 
 THE HIGH PRESSURE SYSTEM. 
 
 strong they might be. For the expansive force of 
 water is almost irrepressible, in consequence of its 
 possessing but a very small degree of elasticity ; and 
 the increase which takes place in its volume, by 
 raising the temperature from 39° (the point of 
 greatest condensation) to 212, is equal to about ^-V 
 part of its bulk, and at higher temperatures the 
 expansion proceeds still more rapidly \ 
 
 171. The temperature of these pipes, when thus 
 arranged, can be raised to a very great extent ; for 
 being completely closed, and all communication cut 
 off from the atmosphere, the heat is not limited, as 
 usual, to the point of 212°, because the steam which 
 is formed is prevented from escaping, as it does in the 
 common form of hot-water apparatus. The most 
 important consideration respecting it, however, is 
 the question as to its safety ; for most persons are 
 aware that steam, when confined beyond a certain 
 point of tension, becomes extremely dangerous ; and 
 in this apparatus the boundary of what has hitherto 
 been used in other cases is very far exceeded. 
 
 172. On the first introduction of this plan, it was 
 usual to make the coil consist of one-fourth part of 
 the total quantity of pipe which was used in the ap- 
 paratus ; and it was considered that when this pro- 
 portion was observed, the heat of the pipes could not 
 be raised so high as to endanger them by bursting. 
 
 ' See Table IV. 
 
THE HIGH PRESSURE SYSTEM. 
 
 135 
 
 But in practice this has not always proved a preven- 
 tive to accident, even when the proportion which the 
 coil bears to the radiating surface is much smaller 
 than is here mentioned, 
 
 173. The average temperature of these pipes is 
 stated to be generally about 350° of Fahrenheit. But, 
 a most material difference of temperature occurs in 
 the several parts of the apparatus ; the difference, 
 amounting sometimes to as much as 200° or 300°. 
 This arises from the great resistance which the water 
 meets with, in consequence of the extremely small 
 size of the pipes, and also from the great number of 
 bends, or angles, that of necessity occur, in order to 
 accumulate a sufficient quantity of pipe. In these an- 
 gles, the bore of the pipe, already extremely small, is 
 still farther reduced, which causes the water to flow 
 so very slowly, that a gre^it portion of its heat is given 
 out, long before it has circulated round the building 
 which is to be warmed. The temperature of the 
 coil, however, is what we must ascertain, if we wish 
 to know the pressure this apparatus has to sustain, 
 and thence to judge of its safety : for by a funda- 
 mental law of hydrostatics, whatever is the greatest 
 amount of pressure on any part of the apparatus, 
 must also be the pressure on every other part. 
 
 174. Now the temperature of this apparatus is 
 found to vary, not only with the intensity of the 
 heat of the furnace, but also with the proportion 
 which the surface of the coil bears to the surface of 
 
136 THE HIGH PRESSURE SYSTEM. 
 
 the pipe which radiates the heat. In some appa- 
 ratus, if that part of the pipe which is immediately 
 above the furnace be filed bright, the iron will be- 
 come of a straw colour, which proves the tempera- 
 ture to be about ^ 450°. In other instances it will 
 become purple, which shows the temperature to be 
 about 530°; while, in some cases, it will become of 
 a full blue colour, which proves that the temperature 
 is then 560°. By this means the pressure on the 
 pipes may be known ; for as there is always steam 
 in some part of the apparatus, the pressure may be 
 calculated as soon as the temperature is ascertained. 
 By referring to Table I. we shall find that a tempe- 
 rature of 450° produces a pressure of 420 lbs. per 
 square inch, while a temperature of 530° makes 
 the pressure 900 lbs.; and when it reaches 560°, the 
 pressure is then 1150 lbs. per square inch. 
 
 175. Those who are acquainted with the working 
 of steam engines, are aware that a pressure of 45 to 
 48 lbs. per square inch is considered as the maxi- 
 mum for high pressure boilers : but we see that in 
 this apparatus the pressure varies from ten times to 
 twenty-four times that amount. And it will also be 
 borne in mind, that, in consequence of the extremely 
 small quantity of water used in these pipes, the 
 slightest increase in the heat of the furnace will 
 cause an immediate increase in the pressure on the 
 
 See Table VI. 
 
THE HIGH PRESSURE SYSTEM. 
 
 137 
 
 whole apparatus. For it appears, by a reference to 
 the Table last mentioned, that if the temperature of 
 the pipes be increased 50° above the amount before 
 stated, the pressure will be raised to 1800 lbs. per 
 square inch ; and by increasing the temperature 
 40° more, the pressure will be immediately raised 
 to 2500 lbs. per square inch; so that any accidental 
 circumstance, which causes the furnace to burn 
 more briskly than usual, may, at any moment, in- 
 crease the pressure to an immense amount. 
 
 176. The pipes which are used for this apparatus 
 are stated to be proved with a pressure of 2800 lbs. 
 per square inch \ This is very probable : for as 
 wrought iron, of the best quality, requires a longitu- 
 dinal strain of 55,419 lbs. to break a bar one inch 
 square ; so the force necessary to break a wrought 
 iron pipe, of one-inch diameter externally, and half- 
 an-inch diameter internally, would be 13,852 lbs., 
 which is equal to 8822 lbs. per square inch on the 
 internal diameter. But, on account of the expan- 
 sive force of the water and steam being transverse 
 to the grain of the iron, and, also, in consequence of 
 the welded joint of the pipe not being so strong as 
 the solid metal, these pipes will not bear any thing 
 like the calculated amount of pressure. It is evi- 
 dent, however, that no ordinary force can burst them ; 
 
 * As pipes are always proved when they are cold, this does 
 not at all show the strain they will bear when heated. On this 
 subject see the following note. 
 
138 
 
 THE HIGH PRESSURE SYSTEM. 
 
 but as this casualty does sometimes occur, this great 
 strength of the materials proves the impossibility of 
 regulating the temperature in hermetically sealed 
 pipes, so as to keep the expansive force of the steam 
 within even this immense limit. 
 
 177. Although this description of apparatus has 
 been erected by many different individuals, possess- 
 ing various degrees of mechanical knowledge, and 
 severally performing their work with different de- 
 grees of excellence, much uniformity appears in the 
 result, in those cases where failure has occurred. 
 From a comparison of a number of cases where acci- 
 dents have happened to apparatus erected on this 
 system, more than one-half have arisen from the 
 bursting of the coil, notwithstanding the increased 
 size of the expansion pipe renders this apparently 
 the weakest part of the apparatus ; the relative 
 strength of pipes, with the same thickness of metal, 
 being inversely as their diameters. 
 
 178. The cause of the explosions occurring prin- 
 cipally in the coil, is owing to the iron becoming 
 weaker in proportion as its temperature is raised ; 
 so that, as the pressure increases, the iron decreases 
 in strength to resist the strain \ Another circum- 
 
 ' The temperature of maximum strength for cast iron has been 
 estimated at about 300° ; but the " Committee on the Explosion 
 of Steam Boilers," appointed by the Franklin Institution, con- 
 sider that the maximum for wrought iron is somewhat higher. 
 After the temperature of maximum strength is once passed, the 
 decrease in the strength of wrought iron is very rapid : at a red 
 
THE HIGH PRESSURE SYSTEM. 
 
 139 
 
 stance also tends to produce the same elfect. It is 
 found, on breaking one of these pipes after it has 
 been used for some time in or near the fire, that the 
 iron has lost its fibrous texture, and that it presents 
 a crystallized appearance, similar to what is known 
 as " cold short iron." This singular change in the 
 texture of iron has been noticed in other instances. 
 Mr. Lowe {Brit. Sci Rep. 1834), has found that 
 wrought iron at a red heat, exposed to the steam of 
 water for a considerable time, becomes crystallized ; 
 and in many other instances also, even without the 
 presence of steam, the same effect has been ob- 
 served. It is not easy to account for this pheno- 
 menon on any of the known chemical properties 
 and habitudes of iron ; but, whatever may be the 
 cause, the effect undoubtedly is to weaken the 
 tenacity and cohesive strength of the metal. 
 
 179. But we shall find that, enormous as the 
 pressure appears to be with which these pipes are 
 proved, it is quite inadequate to the working pres- 
 sure which they sometimes have to resist. It has 
 been ascertained that the relative strength of wrought 
 iron at 300° and at 800° is about as 6 to 1 ; there- 
 fore, if the temperature of the iron, above 300°, 
 
 heat, or about 800°, it is only one-sixth of the maximum ; so 
 that in a range of less than 500° it loses five-sixths of its strength. 
 The maximum strength of copper, on the contrary, is at a very 
 low temperature ; for the strength increases with every reduction 
 of temperature, down to 32°, which is the lowest that has been 
 tried. — Journal of the Franklin Institution, 1836. 
 1 
 
140 THE HIGH PRESSURE SYSTEM. 
 
 increases in an arithmetical progression whose ratio 
 is 100, the relative strength will decrease in an 
 arithmetical progression whose ratio is 1 ; so that 
 we shall have — 
 
 Temperature, 300° 400° 500° 600° 700° 800° 
 Strength, 6 5 4 3 2 1 
 
 Now, according to this relative decrement of 
 strength, when the working pressure on pipes which 
 are heated to 600°, is 1600 lbs. per square mch\ the 
 iron at that temperature being reduced in strength 
 one half from its maximum, the proof pressure, 
 when the pipes are cold, should be 3200 lbs. per 
 square inch. By the same rule we shall find, that if 
 the pipes are to be used at higher temperatures, the 
 proof pressure, when cold, should be as follows : — 
 
 Temperature of Pipe Proof Pressure when cold, 
 
 when in Use. in lbs. per Square Inch. 
 
 And if we farther consider, that, after the iron has 
 been in use for some time, at a high temperature, 
 it loses its fibrous texture, and becomes, in its crys- 
 tallized state, only equal in strength to cast iron, 
 which is, at an average, less than one half the 
 
 650° 
 
 700° 
 
 750° 
 
 5,500 
 9,900 
 18,600 
 
 ' See Steam Pressures, Table 1. 
 
THE HIGH PRESSURE SYSTEM. 
 
 141 
 
 strength of wrought iron^ it will appear that the 
 proof pressure, when cold, for pipes which are to be 
 used in this kind of apparatus, ought, in fact, to be 
 double the amount here stated, and therefore, very 
 much greater than the amount to which they are 
 actually proved. But the pressure which is here 
 stated is obviously more than the iron could sustain; 
 and hence the cause of the pipes bursting after they 
 have been in use for some considerable time, if they 
 happen accidentally to get heated to very high 
 temperatures. 
 
 180. The question has sometimes been asked, 
 What would be the effect on this apparatus if the 
 expansion pipe were to be filled with water, as well 
 as the small circulatory pipe ? The almost imme- 
 diate consequence would be the bursting of the 
 pipes ; for scarcely any thing can resist the expan- 
 sive power of water. The force necessary to resist 
 its expansion, is equal to that which is required for 
 its artificial condensation. Now, at the tempera- 
 ture of 386°, water expands rather more than ^ of 
 its bulk ; and, to condense water this extent (Note, 
 Art. 19), requires a pressure of 27, 104 lbs. per square 
 inch: therefore, in an apparatus containing 800 
 feet of pipe, the bursting pressure, at this tem- 
 perature, on the circulating and expansion pipe 
 
 1 Professor Barlow, On the Strength of Materials. — Brit, 
 Set. Rep. vol. ii. 
 
142 
 
 THE HIGH PRESSURE SYSTEM. 
 
 together^ would be 417,022,l441bs. ! But as no- 
 thing could resist such a force as this, the apparatus 
 would burst before it reached even a fractional 
 part of this immense amount. For if the pipes 
 were filled completely full of cold water, without 
 allowing any room for expansion, and if they were 
 then hermetically sealed, as before described, by 
 increasing the temperature of the water only about 
 60°, the expansion of the water would cause a 
 pressure of 2000 lbs. per square inch, on every part 
 of the apparatus, reckoned by the internal measure- 
 ment. 
 
 181. The assertion has often been made, that the 
 heated fluid contained in an apparatus constructed 
 on this plan, will not scald, even if the pipes 
 should chance to burst, because higli-pressure steam, 
 it is well known, is not injurious in this respect. 
 But this is quite a mistaken notion ; for high-pres- 
 sure hot water will scald, though high-pressure 
 steam will not; and the fluid which would issue 
 through any fissure that might occur in these pipes, 
 could only be partially converted into steam, unless 
 its temperature were at least 1200°. This is ob- 
 viously impossible ; but were it the case, the water 
 would be all converted into steam the instant that 
 it issued from the pipe. The reason that high- 
 
 ^ The steam being an expansive force from within, the pres- 
 sure is only exerted on the inside measurement of the pipes. 
 
THE HIGH PRESSURE SYSTEM. 
 
 143 
 
 pressure steam does not scald, is in consequence of 
 its capacity for latent heat being greatly increased by 
 the high state of rarefaction it instantaneously 
 assumes when suddenly liberated : this lowers its 
 sensible temperature, and causes it to abstract heat 
 from every thing that it comes in contact with. 
 The scalding effect of high-pressure hot water, on 
 the contrary, when suddenly projected from a pipe 
 or boiler by explosion, will always be the same, 
 whatever its temperature, while confined within the 
 pipe, may be ; for the instant it is liberated, a 
 portion of it is converted into steam, and the 
 remainder sinks to the temperature of about 212°. 
 
 182. Among the advantages which have been 
 supposed to arise from the use of this invention, it 
 has |beenj imagined that, in consequence of the 
 quantity of water which the pipes contain being so 
 small, the consumption of coal would be less with 
 this than with any other description of hot-water 
 apparatus. We have seen, however, (Art. 154), 
 that the quantity of coal which is used, is in pro- 
 portion to the heat that is given off in the room 
 that is warmed; and a reference to the Table, 
 Art. 154, will show that the size of the pipe makes 
 no difference in the consumption of coal per hour, — 
 the only difference being in the length of time 
 required to warm the water in the first instance. 
 But there will, on the contrary, be a greater expen- 
 diture of fuel in this apparatus, in consequence of 
 
144 
 
 THE HIGH PRESSURE SYSTEM. 
 
 the coil affording less surface for the fire to impinge 
 against, than would be obtained by using a boiler. 
 In addition to this, the colder any surface may be, 
 when exposed to the action of a fire, the more heat 
 will it receive in a given time ; therefore, as the 
 heat of these pipes is nearly three times as great as 
 that of a boiler, there must be a considerable waste 
 of fuel from this cause. 
 
 183. In consequence of the intense heat of these 
 pipes, it is sometimes found that rooms which are 
 heated by them, have the same disagreeable and un- 
 wholesome smell which results from the use of hot- 
 air stoves and flues. In reality, the cause is the 
 same in both cases ; for it arises partly from the 
 decomposition of the particles of animal and vege- 
 table matter that continually float in the air, and 
 partly from a change which atmospheric air under- 
 goes, by passing over intensely heated metallic sur- 
 faces \ From some experiments recorded in the 
 PJiUosophical Transactions of the Royal Society, 
 made with a view of ascertaining the effect pro- 
 duced on the animal economy by breathing air 
 which has passed through heated media, it appears 
 that the air which has been heated by metallic sur- 
 faces of a high temperature, must needs be exceed- 
 
 * The exact nature of this change which the air undergoes has 
 not been ascertained ; but whatever be the chemical alteration 
 which occurs, a physical change undoubtedly takes place, by 
 which its electrical condition is altered. 
 
THE HIGH-PRESSURE SYSTEM. 
 
 145 
 
 ingly unwholesome. A curious circumstance is re- 
 lated in reference to these experiments, which is 
 illustrative of this fact : — 
 
 " A quantity of air which had been made to pass 
 through red-hot iron and brass tubes, was collected 
 in a glass receiver, and allowed to cool. A large 
 cat was then plunged into this factitious air, and 
 immediately she fell into convulsions, which, in a 
 minute, appeared to leave her without any signs of 
 life. She was, however, quickly taken out and 
 placed in the fresh air, when, after some time, she 
 began to move her eyes, and, after giving two or 
 three hideous squalls, appeared slowly to recover. 
 But on any person approaching her, she made the 
 most violent efforts her exhausted strength would 
 allow, to fly at them, insomuch that in a short time 
 no one could approach her. In about half an hour 
 she recovered, and then became as tame as before." 
 
 184. The high temperature of these pipes, and 
 the intensity at which the heat is radiated from 
 them, has sometimes been urged as an objection 
 against this invention, when applied to horticultural 
 purposes; because, any plants which are placed 
 within a certain distance of them, are destroyed. 
 Although, no doubt, this effect really takes place, it 
 can be easily avoided with proper care ; for, as 
 radiated heat decreases in intensity as the square of 
 the distance, it only requires that the plants should 
 be placed farther off from these pipes than from 
 
 L 
 
146 THE HIGH-PRESSURE SYSTEM. 
 
 those which are of a lower temperature. In com- 
 paring the effect of two different pipes, if one be 
 four times the heat of the other, — deducting the 
 temperature of the air in both cases, — the plants 
 must be placed twice as far off from the one as from 
 the other, in order to receive the same intensity of 
 heat from each. The only inconvenience, therefore, 
 is the loss of room, which, in some cases, may not 
 be of much importance. But a more serious ob- 
 jection by far, appears to lie in the inequality of 
 temperature which any building heated by these 
 pipes must have, in consequence of their being 
 so very much hotter in one part than in another. 
 This difference of temperature between various parts 
 of the same apparatus, has already been stated to 
 amount, in some cases, to as much as 200° or 300*", 
 varying, of course, with the length of pipe through 
 which the water passes. From what has been 
 stated in Chapter IV., it will also be observed 
 that, owing to the smallness of these pipes, this 
 kind of apparatus cools so rapidly w^hen the fire 
 slackens in intensity, that the heat of a building 
 which is warmed in this manner, will be materially 
 affected by the least alteration in the force of the 
 fire, instead of maintaining that permanence of tem- 
 perature which is so peculiarly the characteristic of 
 the hot-water apparatus, with large pipes. 
 
 185. These inconveniences and objections against 
 the apparatus, however, are of but secondary im- 
 
THE HIGH-PRESSURE SYSTEM. 147 
 
 portance in comparison with the question which 
 exists respecting its security. But as there are no 
 means of regulating the temperature in hermetically 
 sealed pipes, so there can be none for limiting the 
 pressure which they sustain : and it is only by me- 
 thods far too refined for general use, that the real 
 amount of the expansive force can be ascertained. 
 An apparatus which to all appearance, therefore, is 
 perfectly safe at any given time of inspection, may 
 in a few minutes afterwards have the pressure so 
 much increased by adventitious circumstances, as to 
 render it extremely dangerous, particularly if its 
 management be confided to unskilful hands: and 
 each day that it is used must add to its insecurity, 
 in consequence of the pipes which form the coil 
 continually becoming thinner by the action of the 
 fire. 
 
 186. This invention undoubtedly exhibits great 
 ingenuity; and, could it be rendered safe, and its 
 temperature be kept within a moderate limit, it would 
 be an acquisition in many cases, in consequence of 
 its facile mode of adaptation. Its safety would 
 perhaps be best accomplished by placing a valve in 
 the expansion-pipe, which, from its large size, would 
 be less likely to fail of performance than one which 
 was inserted in the smaller pipe. If this valve were 
 so contrived as to press with a weight of 135 lbs. per 
 square inch, the temperature of the pipes would not 
 exceed 350° in any part : the pressure would then 
 
 L 2 
 
148 
 
 ROTARY FLOAT CIRCULATOR. 
 
 be nine atmospheres, which is a limit more than 
 sufficient for any working apparatus, where safety is 
 a matter of importance. 
 
 187. An apparatus of a totally different character 
 from the preceding, follows next to be described. 
 It is an invention which, at first, appears to be sin- 
 gularly at variance with the general principles that 
 have been laid down in this treatise ; but, however 
 its mode of action may at first appear to differ from 
 the laws which have been explained, it is certain 
 that, if they are derived from the laws of Nature, 
 they must act equally, at all times, and under all 
 circumstances ; for the operation of the jDhysical laws 
 can never be suspended, though they may be occasion- 
 ally neutralized by a superior antagonist force. In the 
 case of two opposing forces, the resulting action is 
 proportional to their difference of power ; but when 
 the antagonist force is removed, each will act ac- 
 cording to its own peculiar laws. 
 
 188. This is the case with the invention now to 
 be described. By it, hot water is made to descend 
 to any required depth below the boiler, — apparently 
 in opposition to the law of gravity, — while the cold 
 water will ascend, though of greater specific weight. 
 
 189. Eckstein and Busby's Patent Circulator, or 
 Rotary Float, is an invention by which centrifugal 
 force is made to overcome the force of gravity, in 
 the circulation of hot water. The boiler, which is 
 either open or closed at the top, has a pipe a 
 
ROTARY FLOAT CIRCULATOR. 
 
 149 
 
 attached to its circum- 
 ference, which is carried 
 in any direction, either 
 downwards or around the 
 room to be warmed, and 
 
 Fig. -21. 
 
 finally returns into the | | 
 boiler, and ends exactly ^ 
 in its centre, as shown U ''^^ - I 
 
 at b, in the annexed figure. 
 
 190. The float, or circulator, has motion given to 
 it by means of a fly, similar to a smoke-jack, which 
 is placed in the chimney and is turned by the smoke 
 of the fire that is used to heat the boiler, — the float 
 being fixed on centres, and revolving freely in the 
 boiler. The centrifugal force imparted to the water 
 by the rapid rotation of this float, causes it to rise 
 higher at the periphery than in the centre of the 
 boiler ; and the velocity with which the float moves, 
 determines the extent of this deviation from the 
 level. The end of the pipe b, being in the centre, 
 is then under a less pressure, or head of water, than 
 the pipe a, — the former being, by its position, 
 removed from the greater pressure at the sides, 
 which is caused by the centrifugal force imparted to 
 the water by the float, which acts on the pipe a, 
 placed at the circumference. 
 
 191. Suppose now the velocity of rotation to be 
 such as to impart a centrifugal force sufficient to 
 raise the water one mch higher at the circumference 
 
150 
 
 ROTARY FLOAT CIRCULATOR. 
 
 than in the centre, — there will then be a pressure of 
 24 6i grains per square inch, upon the pipe a, more 
 than upon the pipe ^, supposing the temperature of 
 the water to be about 1 80°. This additional pres- 
 sure will allow^ the water in the pipe a to descend 
 42 feet below the boiler, if it does not lose more 
 than 6° of heat before it returns back ao^ain to the 
 boiler- through the pipe^; if it lose 10°, then it will 
 only descend 25^ feet, and so on for other tempe- 
 ratures. Now, as a pipe 4 inches diameter loses 
 •817 of a degree of heat per minute, when its tem- 
 perature is 120° above that of the room (Art. 126); 
 this pipe may be of as great a length as the distance 
 through which the water will flow in seven minutes 
 and a half, in the first case, or twelve minutes in the 
 second. 
 
 192. The length of pipe through which the water 
 will circulate in the abovementioned times, will 
 depend upon the depth to which it descends below 
 the boiler. In this apparatus, the shorter the dis- 
 tance through which the water flows, the greater is 
 the rapidity of circulation ; — an eflect which is the 
 reverse of what occurs in the common form of hot- 
 water apparatus. In general, the circulation is here 
 very rapid ; but the distance through which the 
 w^ater will travel is more limited than with the 
 ^ common plan of circulation. For, suppose the water 
 to be raised, by the centrifugal force, one inch higher 
 at the periphery than at the centre of the boiler. 
 
ROTARY FLOAT CIRCULATOR. 
 
 151 
 
 and that it descends 42 feet ; if the water in the 
 pipe lose 6° of heat during its transit, the circula- 
 tion will then be extremely slow ; because, by the 
 Table, Art. 26, we find that the difference of weight 
 between two columns of water 42 feet high, and 6° 
 difference of temperature, is 242 grains per square 
 inch on the area of the pipe, which is within 4 grains 
 of the weight of the one-inch additional height of 
 the water in the boiler. But if the difference be- 
 tween the temperature of the two pipes be only 4°, 
 then the difference between the weight of the two 
 columns will be 160 grains per square inch of the 
 area of the pipe ; and, by Art. 33, we shall find that 
 this will give a velocity of 81 feet per minute, so 
 that the pipe may in this case be about 400 feet 
 long. But if the water only lose 3° of heat during 
 its transit through the pipes, then (by Art. 33) its 
 velocity will be 100 feet per minute, provided it 
 descends only 42 feet below the boiler ; and there- 
 fore, the pipe may be about 350 feet in length. If 
 the depth of the descent below the boiler be only one 
 half the amount above mentioned, — or 21 feet in- 
 stead of 42, — then the length of pipe through which 
 the water will circulate, will be just double the 
 amount that has been stated for the several differ- 
 ences of temperature. 
 
 193. These calculations are all made for pipes of 
 4 inches diameter ; but if smaller pipes be used, the 
 distance through which the water will circulate, will 
 
152 
 
 ROTARY FLOAT CIRCULATOR. 
 
 be less ; because, as the quantity of heat lost in a 
 given time by different sized pipes, is as the inverse 
 of their diameters, so also will be the distance that the 
 water will flow, if the velocity of its motion be the 
 same^ 
 
 194. If greater velocity be given to the fly-wheel 
 and float, the centrifugal force, and the height of the 
 water at the circumference of the boiler, will both 
 be increased ; and the distances to which the pipes 
 can be carried, may then likewise be extended. 
 
 195. By using a close boiler instead of an open 
 one, a range of pipes may be taken upwards, which 
 will act on the common plan of circulation, while 
 another range of pipes may proceed from the bottom, 
 and act on the principle which has here been ex- 
 plained. In this case the centrifugal force, of which 
 the additional height at the circumference of the 
 boiler is merely the index or measure of effect, 
 will still be of equal power, provided the velocity 
 of the float continues the same ; and the water will 
 therefore descend to the same extent as before. 
 The spindle of the float must, in this latter case, 
 
 ^ It will be observed from what has been stated respecting the 
 common plan of circulation, that the whole of these effects are ex- 
 actly the reverse of what there occurs. In that, the greater the 
 difference of temperature between the pipes, the more rapid the 
 circulation : in this, the circulation is more rapid in proportion as 
 the pipes are nearer to the same temperature. In the former, the 
 circulation is more rapid when the pipes are moderately small : in 
 the latter, the larger the pipe, the greater the velocity of circulation. 
 
ROTARY FLOAT CIRCULATOR. 
 
 153 
 
 pass through a stuffing box on the top of the boiler, 
 or some other contrivance to answer the same pur- 
 pose must be adopted. 
 
 196. This invention, which is a happy application 
 of dynamical principles, to overcome one of the most 
 constant of Nature's laws, by the development of an 
 antagonist force, has hitherto been but little used. 
 It is, however, clearly capable of being efficiently 
 applied, in those cases where the same object cannot 
 be accomplished by any of the more simple means 
 which have been previously described. 
 
 197. Various other forms of hot- water apparatus 
 have been proposed by Price, Fowler, Weeks, Smal- 
 ley, Saul, and others ; and several of these have been 
 made the subject of patents. But none of them 
 appear to merit particular notice, as they present no 
 new features in principle ; the chief object which 
 the inventors have aimed at, being some fancied 
 advantages by adopting peculiar shapes either of the 
 boiler, or the radiating surfaces. Some of these 
 inventions, however, are decidedly erroneous on sci- 
 entific principles, and, of course, objectionable in 
 practice. One of these plans may be mentioned, in 
 which the boiler consists of a number of cast-iron 
 pipes, li or 2 inches diameter, which are fastened 
 together in the form of an arch. These pipes are 
 not only liable to crack by the unequal expansion 
 to which they are subject, but they must also become 
 stopped up in a short time, by the sediment from the 
 
154 
 
 RADIATING SURFACES. 
 
 water, which will, of course, prevent the circulation. 
 Another plan, now nearly, if not wholly, laid aside, 
 consisted in making the flow pipe of about ten or 
 twelve times the area of the return pipe ; a contri- 
 vance, which, by lessening the rapidity of circulation, 
 prevented the full effect of the heat in the boiler 
 from becoming available. 
 
 198. The advantage which may be derived from 
 any peculiar forms of the apparatus, must depend 
 entirely upon the purpose for which it is required. 
 No rule can be laid down which is applicable to 
 every case. But in all places where a long continu- 
 ance and uniformity of temperature are required, the 
 form of the pipes, tanks, boxes, or other radiating 
 surfaces, must be such as to afford only a small sur- 
 face to a large body of water; while, on the con- 
 trary, where these objects are not matters of import- 
 ance, the radiating surface may advantageously be 
 increased, relatively to the quantity of water. This 
 may be accomplished either by using smaller pipes, 
 or by altering the shape of the radiating surfaces ; 
 and a variety of ways of effecting this object, will 
 naturally suggest themselves to an ingenious mind. 
 
CHAPTER X. 
 
 Summary of the Subject, and General Remarks. 
 
 ] 99. Having in the preceding Chapters arranged, 
 under distinct heads, the various remarks on the 
 principles of warming by the circulation of hot 
 water, it may here be desirable to bring under 
 general review, the principal facts which it has been 
 the object of this work to explain. There are, be- 
 sides, many minor points connected with the inven- 
 tion, that could not conveniently be brought under 
 notice in any of the foregoing divisions, under which 
 the subject has been treated, but which, neverthe- 
 less, may be found useful to those who are inves- 
 tigating its principles and application. 
 
 200. A correct knowledge of the cause of circu- 
 lation of the water, it has already been observed, is 
 absolutely necessary to the successful application of 
 this invention in many of its more complicated 
 arrangements. Some estimate must be formed of 
 
 1 
 
156 
 
 GENERAL SUMMARY. 
 
 the amount of the motive power possessed by an 
 apparatus of this sort, otherwise it will be impossible 
 to ascertain what will be the result of any particular 
 position or determinate length of the pipes, in many 
 peculiar cases ; as, for instance, in such forms of 
 apparatus as figures 10, 11, and 21. It is also 
 necessary, in order to make provision for the escape 
 of the air from an apparatus of this kind, to have 
 some knowledge of the laws which regulate the mo- 
 tion of fluids, in order to ascertain where the air 
 will lodge, and why it should accumulate in one 
 place rather than another. No circumstance con- 
 nected with the subject requires greater caution 
 than this. In every part of the apparatus where an 
 alteration of the level occurs, a vent for the air must 
 be provided ; because, from the extreme levity of air 
 compared with water (Art. 13), it is impossible that 
 the air can ever descend, so as to pass an obstruction 
 lower than the place where it is confined. Thus, in 
 fig. 7, if the air accumulate in the pipe between a 
 and ^, it is evident that a vent at c, although it 
 would take off the air from ^, /^, and from c, D, could 
 not receive any portion of that which is confined 
 between a, or between e, f, because, in that case, 
 it must descend through the pipe e,f^ before it could 
 escape. The principle is the same in all cases, 
 however large, or however small the descent may 
 be : and the accidental misplacing of a pipe in the 
 fixing, by which one end may be made a little 
 
GENERAL SUMMARY. 
 
 157 
 
 higher then the other, will as effectually prevent 
 the escape of air through a vent placed at the lower 
 end, as though the deviation from the level were as 
 many feet, as it may, perhaps, be indies. It is, how- 
 ever, impossible to give multiplied examples of this 
 part of the subject, for probably no two instances, 
 precisely similar, may occur; but it deserves the 
 most serious attention in following out its practical 
 consequences, for many failures have arisen from its 
 neglect. 
 
 201. When any particular obstructions are re- 
 quired to be overcome, in consequence of numerous 
 alterations in the level of the pipes ; when the pipes 
 are required to descend below tlie boiler; or, in 
 short, when any other variation from what may be 
 considered as the usual form and arrangement of the 
 apparatus may be desirable, it is essentially necessary 
 to have some data on which to found a calculation 
 as to what will be the practical result of the required 
 deviation ; for no partial experiment of a tentative 
 character, or even the effect shown by a miniature 
 model, will give any thing like an accurate idea of 
 what will be the result, when the experiment is 
 made on a large scale. The reason of this is obvious. 
 It has been shown, that the greater the distance 
 through which the water flows, the greater does the 
 motive power become, in consequence of the water 
 being colder in the return pipe relatively to the flow 
 pipe. This will, therefore, prevent partial experi- 
 
158 
 
 GENERAL SUMMARY. 
 
 ments, — that is, working models, exhibiting only a 
 particular portion of the whole apparatus, — from 
 being conclusive : and, with a miniature model, 
 although the decreased time and distance of transit, 
 are compensated by the reduced size of the pipe 
 exerting a greater cooling power on the water, the 
 friction being much greater in small than in large 
 pipes, the velocity will be reduced in a very sensible 
 degree, and the results rendered wholly inconclusive. 
 In general, the successful working of a miniature 
 model, will be conclusive that the experiment on a 
 larger scale will perform still better ; but the failure 
 of the model will be no proof that the larger appa- 
 ratus will not be successful. 
 
 202. The data on which calculations may be 
 founded, sufficiently accurate for this purpose, have 
 been given in the preceding Chapters; and by 
 following out, in detail, the rules which are there 
 given, a tolerably accurate judgment may be formed, 
 as to the result that may be expected, under almost 
 every form of the apparatus that may be adopted. 
 
 203. The quantity of heating surface required to 
 warm any given space, has been fully discussed in 
 Chapter VIII., as likewise the consumption of 
 fuel, and other matters connected with this part of 
 the subject. The fact, that the consumption of fuel 
 to warm a given space, is irrespective of the size of 
 the pipes, and the quantity of water they contain, 
 is, perhaps, not in accordance with the generally 
 
GENERAL SUMMARY. 
 
 159 
 
 received opinion ; but, nevertheless, it will be found 
 correct, in so far, at least, as regards the maintaining 
 the temperature of a building at a given standard, 
 after the water in the apparatus is heated. But by 
 using moderately small pipes, a saving both of time 
 and fuel will be effected ; because, the smaller the 
 quantity of water employed, the less fuel will it 
 require to heat it to a given temperature. For the 
 greater expenditure of fuel which occurs in conse- 
 quence of using large pipes, is merely owing to the 
 larger body of water requiring a longer time to heat, 
 than would a less quantity ; but, when once the tem- 
 perature of the pipes has attained its equilibrium, 
 it requires only the same quantity of fuel to continue 
 them at that temperature, whatever the size of the 
 pipes may be : therefore, in those buildings in which 
 the heat is constantly maintained, it is quite unim- 
 portant, on the score of economy, what is the size of 
 the pipes ; but in others, pipes of a moderately small 
 size will be found more economical than large ones, 
 and they should therefore be used in those cases 
 where permanence of temperature is not a matter of 
 importance. 
 
 204. The shape and size of the radiating surfaces, 
 or vessels, also makes a material difference in the 
 time requisite to warm a given space to any deter- 
 minate temperature. The greater the surface, 
 relatively to the mass, the more of its heat will the 
 hot body part with in a given time. (Art. 70.) A 
 
160 
 
 GENERAL SUMMARY. 
 
 very great difference obtains in this respect, in 
 different cases : for one body will cool three or four, 
 or even eight or ten times as rapidly as another ; 
 and by sufficiently increasing the surface, in propor- 
 tion to the mass, almost any degree of rapidity of 
 heating a room or building may be attained. In 
 many cases, however, this rapidity of heating is 
 attended with considerable disadvantage ; for the 
 apparatus is then unable to retain its heat for a 
 sufficient length of time, after the fire is extin- 
 guished. 
 
 205. In the preceding pages, all mention of the 
 mechanical operation of fitting together the different 
 parts of the apparatus, has purposely been avoided ; 
 neither is it here intended to enter into the subject. 
 The necessary knowledge for this purpose is easily 
 acquired by a good workman, even if he do not 
 already possess it. The only part, therefore, which 
 it is proposed to allude to, is the erroneous notion 
 which some persons entertain respecting the joints 
 of the pipes. That these require to be well made, 
 there is no question ; but to ensure their soundness 
 or strength, it is by no means necessary, as some 
 persons suppose, to use flange pipes : on the con- 
 trary, not only are socket pipes both neater, and less 
 liable to leak, but it is doubtful whether they are not 
 even stronger than flange joints. If the joints of 
 the socket pipes be put together with iron cement, 
 the pipe itself will break, before the faucet end of 
 
GENERAL SUMMARY. 
 
 161 
 
 the one pipe, can be drawn out of the socket of the 
 other. In a hot-water apparatus, there is no expan- 
 sive force employed which could, under any circum- 
 stances, force the pipes asunder; and, even for 
 steam pipes, it is probable that, contrary to the 
 usual practice, socket joints might be employed with 
 advantage, and that economy and superior neatness, 
 united with an equal degree of strength, would 
 result from their use. 
 
 206. There are a great number of useful purposes 
 to which this principle of heating is applicable, but 
 to which it has hitherto been but sparingly applied, 
 though it offers the promise of great utility. Such 
 are the uses to which it may be adapted in various 
 manufactories, — in paper-making, calico-printing, 
 dyeing, and starch-making ; and also for druggists, 
 seedsmen, and innumerable other purposes of general 
 utility. For many of these purposes it is exceed- 
 ingly convenient, as the form of the heating surface 
 can be made of any shape to suit the peculiar 
 object ' to which it is to be applied ; and its equality 
 of temperature prevents all those inconveniences 
 
 ^ One of the most ingenious applications of hot water that I 
 have seen, is a kiln erected for Messrs. Keen, and Co. of Garlick 
 Hill, Upper Thames Street. The whole floor of the kiln presents 
 a surface which is warmed by the water circulating through it, 
 and nothing appears which could reveal the method by which the 
 heat is obtained. The saving is found to be very great, both in 
 the preservation of the articles which are dried in it, and also by 
 the great economy of fuel. 
 
 M 
 
162 
 
 GENERAL SUMMARY. 
 
 that arise from unequal degrees of heat, which are 
 consequent on most other of the existing methods 
 of warming. 
 
 207. All the rules which have been given in the 
 previous pages, have been framed to suit the cases 
 of most common occurrence. There are some cases, 
 however, where apparatus of great magnitude are 
 required, in which these rules will not apply without 
 modification : but as such instances are of compara- 
 tively rare occurrence, and farther, as no person 
 that is a novice in the practical application of this 
 principle of warming, will be likely to undertake, for 
 his first essay, the erection of an apparatus of gigantic 
 dimensions, it is the less necessary to enter at length 
 into such cases as it may be supposed will render 
 any alteration of these principles necessary. It 
 may, however, be observed, that cases may occur 
 where a different construction of the boilers may be 
 desirable, to that which has been recommended ; for 
 instance, where, from the large quantity of heat 
 required, a furnace of very great power would be 
 necessary; and in that case, a boiler which exposes 
 a large surface, while it possesses only a small capa- 
 city, would obviously be injudicious, because the 
 intense heat, acting on a small body of water, would, 
 probably, generate steam of a high degree of elasti- 
 city in the boiler, and not only produce much in- 
 convenience, but even neutralize the effect of what 
 might otherwise be an efficient apparatus. Some 
 
GENERAL SUMMARY. 
 
 163 
 
 cases may occur, where two moderately small boilers 
 will be more economical and effective than one very 
 large one ; and many cases may arise where several 
 flow pipes, taken from different parts of a boiler, 
 will be more advantageous than one large main 
 pipe, particularly when the boiler is very large, or 
 the water is required to circulate at different alti- 
 tudes, varying considerably from each other. The 
 size of the pipes also ought to be regulated, not only 
 by the purpose to which the building is to be 
 applied, but also to the quantity of pipe actually 
 used in the building. For if the distance through 
 which the water has to travel before it returns 
 to the boiler, be very considerable, the size of the 
 pipes ought not to be so small as to cause any very 
 great degree of friction : neither ought they to be 
 too large; because, in this case, the water will never 
 reach so high a temperature as it otherwise would do, 
 and therefore its effect will be proportionably less. 
 
 208. These remarks relate principally to the 
 erection of the apparatus : others, however, may be 
 added, which apply more to its practical working. 
 One not unimportant subject, is the quality of the 
 water which is used. Sometimes the foulest and 
 most filthy water is used in a hot-water apparatus, 
 by which a thick coating of mud is deposited, and 
 which must, necessarily, not only much reduce the 
 effect of the apparatus, but also injure the boiler. 
 But a far more general, and in fact, an extremely 
 
 M 2 
 
164 
 
 GENERAL SUMMARY. 
 
 common error lies in using hard water, which contains 
 a large quantity of earthy salts. Rain-water ought 
 always to be used when it can possibly be obtained, 
 because all hard waters are impregnated with saline 
 matter, which forms the sediment, or incrustation, so 
 common in those vessels in which water is boiled. 
 This incrustation always accumulates in the boiler 
 of a hot-water apparatus in which hard water is 
 used, and forms a coating, varying in substance from 
 the thinnest lamina, to two or three inches in thick- 
 ness. When this deposit of saline matter occurs in 
 a boiler, not only is less heat received by the 
 water, in consequence of the conducting power being 
 lessened by the interposed substance, but the boiler 
 will be much injured by the increased heat of its 
 external surface, and more fuel will be consumed. 
 
 209. This kind of sediment can only be removed 
 from a boiler with great difficulty. It consists, 
 principally, of carbonate of lime and sulphate of 
 lime, together with the sulphates of soda and mag- 
 nesia, and several other salts, varying considerably 
 in different localities. A weak solution of muriatic 
 acid (1 part of acid by measure to 20 or 30 parts of 
 w^^er) will generally reduce this concreted sediment, 
 into a substance of less tenacity, which may then be 
 removed with slight mechanical force. By using 
 rain water, the inconvenience arising from these 
 deposits will, however, be entirely avoided, and the 
 apparatus will both last longer and be more efficient. 
 
GENERAL SUMMARY. 
 
 165 
 
 210. Some inconvenience has occasionally been 
 experienced when a hot-water apparatus has been 
 left for a long time without being used, and exposed 
 to considerable degrees of cold, by the water be- 
 coming frozen in the pipes ; for it is not only diffi- 
 cult in such cases to thaw the water, but sometimes 
 also the pipes crack. To prevent this, it will gene- 
 rally be sufficient to draw oif a portion of the water, 
 so that the horizontal pipes shall not be quite full ; 
 for the cracking of the pipes arises from the sudden 
 expansion which takes place in the water, at the 
 moment of its passing into the solid state of ice. 
 But when the apparatus is not likely to be used for 
 a considerable time, it would be much better, if the 
 weather be very cold, to empty the pipes entirely of 
 water; for it is always troublesome to thaw the 
 water when once frozen in the pipes. But in an 
 apparatus used in a building of which the tempera- 
 ture is always above 32°, this is obviously unneces- 
 sary, as the water cannot then be frozen. A plan, 
 however, might be adopted which would effectually 
 prevent the water freezing with any ordinary degree 
 of cold ; namely, by using salt water in the appa- 
 ratus, instead of fresh water. This plan would cer- 
 tainly be somewhat injurious to the apparatus, on 
 account of the action of the salt on the iron; but 
 the injury would not be at all extensive, and would 
 be very slow in its operation. Perhaps in this 
 country such a plan is unnecessary ; but should this 
 
166 
 
 GENERAL SUMMARY. 
 
 kind of apparatus be adopted in colder climates, the 
 suggestion might be useful. The larger the quantity 
 of salt which a given portion of water contains, the 
 greater is the degree of cold necessary to congeal it. 
 Thus, the quantity of salt contained in sea water is 
 about 3|- per cent.^; this requires, according to 
 Dr. Marcet, a temperature of about 28° to freeze it : 
 but if the quantity of salt be increased to 4*3 per 
 cent., the water will not freeze until the cold be 
 reduced to 27^° of Fahrenheit, or 4^° below the 
 ordinary freezing point of fresh water. When the 
 water contains 6'6 per cent, of salt, it will not 
 freeze until the temperature be reduced to 25|- of 
 Fahrenheit; and if it contains 11*1 per cent., the 
 temperature must reach as low as 21^ before the 
 water will congeal. 
 
 211. The effect which would be produced on cast- 
 iron pipes and boilers, by any of these quantities of 
 salt, would not be of much importance ; although, in 
 process of time, it would certainly, in some degree, 
 corrode the apparatus^. When the apparatus has 
 
 ^ This quantity varies considerably in different localities. In 
 the English Channel the quantity is as above stated ; but on the 
 coast of Spain it contains about 6 per cent., while the water of 
 the Baltic only contains about 1^ per cent. Between the Tropics 
 the quantity is very large ; — as much as 10 per cent, is stated to 
 exist in some of the tropical seas and oceans. 
 
 ^ A remarkable difference obtains in the rate at which oxyda- 
 tion acts on cast and on wrought iron. Hard cast iron will resist 
 oxydation about three times as long as wrought iron ; and, 
 according to the experiments of Mr. Daniell, the same difference 
 
GENERAL SUMMARY. 
 
 167 
 
 been once filled with salt water, the waste which 
 occurs in the water, by evaporation, should only be 
 supplied with fresh water ; for as the salt does not 
 evaporate, the same quantity of salt will remain in 
 the apparatus, and will combine with the fresh water 
 when added. 
 
 212. As water can hold in solution as much as 35 
 per cent, of common salt (chloride of sodium), there 
 is no fear of any deposit forming in the boiler from 
 this cause. The reason of a deposit forming in boilers 
 where hard water is used, is, because the water 
 leaves behind, on evaporation, the saline compounds 
 which it held in solution ; and as the water which is 
 added to supply the place of that which has evapo- 
 rated likewise contains the same extraneous matter, 
 the quantity presently becomes larger than the water 
 can hold in solution, and the residue is precipitated 
 and hardened by the heat of the fire. All the salts 
 of lime, which are usually contained in hard water, 
 are, likewise, soluble in this fluid only in a very 
 limited degree. For instance, sulphate of lime, one 
 of the most common ingredients in hard water, is 
 soluble in it only to the extent of f per cent., and 
 carbonate of lime in a still smaller proportion ; there- 
 fore the precipitation begins to take place as soon as 
 the quantity exceeds this small amount. 
 
 exists in the length of time requisite to produce a given effect by- 
 acids. The effect on soft cast iron will approach nearer to that 
 of wrought iron, varying with its hardness. 
 
168 
 
 GENERAL SUMMARY. 
 
 213. The necessity which exists for making suffi- 
 cient provision for the expansion, both of the pipes 
 and the water contained in them, has been men- 
 tioned in Chapter II. ; and the requisite informa- 
 tion respecting the sizes proper for the boilers, 
 furnaces, main pipes, &c., has been given in 
 Chapters III., IV., V. It, therefore, only remains 
 to observe, that when these rules are followed, no 
 doubts need be entertained, as to the successful and 
 safe performance of any apparatus erected conform- 
 ably to them : and, any one possessing an apparatus 
 constructed on these principles, has, what should 
 always be an object of paramount importance in 
 such matters, a machine that requires no care nor 
 attention, and of which the efficiency of performance 
 for many years may be calculated on with certainty. 
 
 It may, however, be remarked, that many appa- 
 ratus which have proved wholly abortive, as to any 
 beneficial effect, have failed through the most tri- 
 fling causes ; so trifling, indeed, that it may safely 
 be said, that alterations, which, if properly directed, 
 would not, in some cases, have cost more than a few 
 shillings in amount, would have converted the use- 
 less and unprofitable machine into a perfect and 
 efficient apparatus. In many of these instances, the 
 apparatus has been removed and destroyed, and the 
 whole cost sacrificed; though, had the opinion of 
 some scientific person been obtained, this waste and 
 destruction of property might have been avoided. 
 
CHAPTER XI. 
 
 ON VENTILATION. 
 
 Effects of Respiration, and the Chemical and Physical Alteration 
 of the Air — Amount of Ventilation — Rules for Calculating the 
 Proper Size for Ventilators — Different Methods of Producing 
 Ventilation — Importance of Ventilation on Health. 
 
 214. No system of warming buildings, however 
 good of itself, can be considered perfect without it 
 is accompanied by sufficient ventilation. The best 
 plan of artificial heat becomes inefficient without it ; 
 but with good ventilation, even the worst system of 
 warming may be rendered tolerable. 
 
 215. Ventilation is a subject which has always 
 attracted far less attention than it deserved. The 
 general principles which are known, are seldom 
 applied in a systematic manner. In small buildings 
 it is in general wholly overlooked ; and, in those of 
 a larger description, where it becomes impossible 
 entirely to neglect it, it generally fails in regard to 
 quantity. In fact, the fundamental principles of 
 ventilation are so simple, that almost the only diffi- 
 
170 
 
 REMARKS ON 
 
 culty, except in some few extraordinary cases, is to 
 apportion the proper amount, so that the ventilators 
 shall be sufficiently large, without causing any unne- 
 cessary waste of heat. Some calculations on this 
 subject may, therefore, perhaps, be useful. 
 
 216. In inhabited rooms, the quantity of air 
 which is vitiated by the inmates varies considerably 
 under different circumstances. When an individual 
 is in a state of repose, the quantity of oxygen con- 
 sumed, and the amount of vapour expulsed from the 
 system, are much inferior to what they are when 
 muscular exertion is used. It is, therefore, evident, 
 that the ventilation of a manufactory, or of a ball 
 room, ought to be much greater than is necessary 
 for churches, lecture-rooms, concert-rooms, or any 
 other building where the inmates are in a state of 
 quietness and inactivity. 
 
 217. Lavoisier ascertained that the consumption 
 of oxygen by a man, while engaged in strong mus- 
 cular exertion, compared with the same individual 
 while in a state of repose, was in the proportion of 
 32 to 14; and the quantity of vapour given off by 
 the body, under different states of activity, is also 
 found to vary in the same proportion. 
 
 218. The amount of the vapour which is discharged 
 from the lungs, is variously stated by Menzies, Sanc- 
 torius, Abernetliy, and Hales, at 6, 8, 9, and 20 
 ounces in 24 hours. The amount of perspiration 
 from the skin, Keil found, by experiments made 
 
VENTILATION. 
 
 171 
 
 upon himself, to be 31 ounces in 24 hours, or 10|- 
 grains per minute; but, according to Thenard, it 
 varies from 9 to 26 grains per minute. The quan- 
 tity of vapour thus given off from the system varies, 
 however, not only under the different degrees of 
 muscular exertion and repose, but also under the 
 ever changing hygrometric condition of the atmos- 
 phere : for the greater the quantity of vapour which 
 the air contains, the less will it be able to carry off 
 from the human body. For the air possesses a 
 desiccating power on the human body ; but, of 
 course, that power is lessened in proportion as it is 
 nearer to the point of saturation. 
 
 219. The hygrometric condition of the atmosphere 
 is ascertained by the dew point ^ The lower is the 
 dew point, the more moisture will be carried off 
 from the lungs by the air, in respiration ; and, there- 
 fore, less will be given off by perspiration, than 
 when the dew point is higher. This is often the 
 case in very cold weather, when a large quantity of 
 vapour is carried off from the lungs, and but little 
 
 ' The dew point is that thermometric temperature of the at- 
 mosphere at which vapour is condensed. By exposing a cold 
 body to the air, a fine dew is deposited on its surface, and, by 
 observing the temperature of this cold body, we know the exact 
 quantity of vapour contained in the air at that time. Warm air 
 contains a larger quantity of vapour than that which is colder ; 
 for air has the property of taking up water in solution in a quan- 
 tity proportional to its temperature. The Table II. shows the 
 quantity of vapour that the air contains when the dew point is 
 obtained in this manner. 
 
172 
 
 REMARKS ON 
 
 by perspiration. When air is respired from the 
 lungs it is nearly of the temperature of the blood, 
 ■which is 98° Fahrenheit ; and it is then charged 
 with a large quantity of vapour. If we ascertain the 
 quantity of vapour which the air contains when ex- 
 pired, and deduct what it possessed before it was 
 inhaled, we shall learn the amount given off by the 
 lungs ; the quantity of air breathed per minute being 
 known. Now, suppose the temperature of the air, 
 before it is inhaled, to be 40°, and the dew point 
 30° ; as 800 cubic inches of air is the average quan- 
 tity breathed per minute, Yy^- of a grain ^ of vapour 
 will be received into the lungs with the air, per 
 minute. But when the air is again expired, the 
 temperature will be about 95°, and the dew point 
 probably about 85° : it will then contain 5*6 grains 
 of vapour in the 800 cubic inches ; so that upwards 
 of 4i grains per minute are given off from the lungs 
 under these circumstances. But if the dew point of 
 the air, before it is breathed, be 50°, which is fre- 
 quently the case in damp or warm weather, then 
 only 3i grains of vapour will be given off in the 
 same time. Dr. Dalton states, that in the torrid 
 zone, the dew point sometimes rises to 80°, and that 
 even in this country it occasionally reaches to 60°, 
 while, in winter, it is sometimes below zero. This 
 easily accounts for the variable quantity of moisture 
 
 See Table II. 
 
VENTILATION. 
 
 173 
 
 which is exhaled from the body and lungs at 
 different times. 
 
 2'20. The atmosphere, during damp weather, when 
 it is frequently nearly in a state of saturation, is 
 unable to carry off the full quantity of vapour from 
 the body. This causes the oppressive sensation that 
 is so often experienced under such circumstances ; 
 and the slightest exertion causes the perspiration to 
 condense upon the surface of the body, and a degree 
 of heat is experienced, much greater than the simple 
 thermometric temperature would occasion. This is 
 often the case likewise in badly ventilated rooms. 
 Here, however, another cause augments the incon- 
 venience : for experiments have proved, that air, 
 which has been once inhaled, loses about 10 per 
 cent, of its oxygen, or nearly one half that it con- 
 tains, and acquires from 8 to 8^ per cent, of carbonic 
 acid gas. This gas, it is well known, is as destruc- 
 tive to animal life as the oxygen is necessary for its 
 preservation, and, therefore, air cannot be breathed 
 a second time without serious inconvenience. For, 
 as it is found impossible to make atmospheric air 
 contain more than 10 per cent, of carbonic acid gas, 
 it follows, that, if breathing a quantity of air once, 
 impregnates it with per cent, of this gas, if it be 
 breathed a second time, it can only receive 1|- per 
 cent.; and, therefore, the remainder must be left in 
 the lungs, where it exerts a most deleterious effect. 
 The noxious qualities of this gas are well known ; 
 
174 
 
 REMARKS ON 
 
 the foul air of wells, which causes death in so many 
 instances, consists of this deleterious matter: and 
 it is extraordinary that the heart and muscles of 
 any animal that has been deprived of life by breath- 
 ing it, entirely lose their irritability, and become in- 
 sensible even to the powerful stimulus of galvanism. 
 
 221. Although the carbonic acid gas, given off 
 from the lungs, is rather more than 37 per cent, 
 heavier than the oxygen which is consumed, still, in 
 consequence of the dilatation of its volume by the 
 increased heat, and the greater levity of the vapour 
 given off from the lungs, the air is specifically lighter 
 at the moment of its expiration than at its inspira- 
 tion. For 800 cubic inches of pure air at the tem- 
 perature of 60°, and the dew point 40°, will weigh 
 243*395 grains ; but 800 cubic inches of air at 95°, 
 containing 8^ per cent, of carbonic acid gas^ and 
 
 * The quantity of carbon given off from the lungs being so 
 considerable, we cannot wonder that the subject of its origin has 
 been a deeply disputed question. Supposing 68 cubic inches of 
 carbonic acid gas to be given off from the lungs per minute, on 
 an average, that quantity will contain 8'63 grains of pure carbon, 
 which in 24 hours will amount to 28 ounces. As this frequently 
 exceeds the total quantity of food consumed in a day, it would 
 seem impossible that the food were the only source which yields 
 this substance : for, besides this, if the quantity of vapour from 
 perspiration and pulmonary transpiration, be taken at 10 grains 
 per minute for the former, and 3 grains for the latter, they will 
 amount to 42 ounces in 24 hours, making the vapour and carbon 
 together amount to nearly 4jlbs.; besides other excrementitious 
 matter from the body. Some other source, then, besides the food, 
 must exist for obtaining the matter which supports vitality, and 
 this probably is the air. We have already seen that expired air, 
 
VENTILATION. 
 
 175 
 
 5*6 grains of vapour, with the dew point 85°, will 
 only weigh 232*450 grains, being nearly 5 per cent, 
 lighter. Hence air, when expired from the lungs, 
 always rises upwards, and will flow through ventila- 
 tors in the ceiling, or the upper part of the walls of 
 a room, if such be provided for its escape; but, 
 otherwise, the vapour condenses, and the volume of 
 the air collapses as it cools ; it then becomes heavier 
 than the substrata of air, and sinks to the lower part 
 of the room contaminated with impurities. 
 
 is of less weight than the inspired, and it is probable that there 
 is an absorption of it in the system to some considerable extent. 
 It has been ascertained by Dr. Prout, that a vegetable diet 
 diminishes the quantity of carbonic acid gas given off, and, of 
 course, reduces the quantity of oxygen consumed; because car- 
 bonic acid gas contains exactly its own bulk of oxygen, united 
 to the given weight of pure carbon. The accuracy of Dr. Prout's 
 experiments has been confirmed by divers and persons making 
 use of the diving bell. In all hot climates, also, where, from the 
 rarified state of the air, less oxygen is received at each inspiration 
 than in the higher latitudes, the inhabitants feel but little desire 
 for animal food, and use, principally, a vegetable diet ; while, on 
 the contrary, the inhabitants of the Arctic regions use animal 
 food almost exclusively. Dr. Richardson, who accompanied 
 Capt. Franklyn on his voyage of discovery to the Polar seas, 
 says, that himself and the other individuals, who composed the 
 expedition, never felt the slightest wish for vegetable diet, but 
 desired the most stimulating animal food, and in much larger 
 quantities than they had ever before been accustomed to. In such 
 a climate, in consequence of the coldness and density of the at- 
 mosphere, the quantity of oxygen inhaled is much greater than 
 in warmer regions, and therefore allows the larger quantity of 
 carbon to be carried off, which the dieting on animal food pro- 
 duces. These results, therefore, accord with Dr. Prout's ex- 
 periments. 
 
176 
 
 REMARKS ON 
 
 222. Such being the effects resulting from want 
 of proper ventilation, it is necessary to inquire what 
 is the quantity of air to be changed per minute, to 
 maintain its purity in inhabited rooms and public 
 buildings. 
 
 223. Although 800 cubic inches of air per minute, 
 is a sufficient pulmonary supply for each individual, 
 a much larger quantity is necessary to carry off the 
 insensible perspiration. The amount of vapour 
 from this cause, we have seen, has been variously 
 stated by different experimentalists; but we may 
 not, perhaps, be far wrong in estimating it, on an 
 average, at 10 grains per minute, when the indivi- 
 dual is not making any particular muscular exer- 
 tions. If the temperature of a room be 60°, the air 
 will absorb 5*7 grains of vapour per cubic foot ; but, 
 the average dew point being about 45°, the air will 
 previously contain 3-5 grains ; so that a cubic foot 
 of air will only absorb an additional quantity of 
 about 2i grains of vapour. Under these circum- 
 stances, the perspiration from the body will saturate 
 4^ cubic feet of air per minute. But in estimating 
 the quantity of air which is to be warmed, in order 
 to allow of sufficient ventilation, this amount may 
 be considerably reduced; because, as 45° is the 
 average dew point for the whole year\ it will be 
 
 ' This is for the neighbourhood of London. It varies, of 
 course, in different places, and is much influenced by the prevail- 
 ing winds. An easterly wind travelling to us from the Conti- 
 
 ] 
 
VENTILATION. 
 
 177 
 
 much lower in winter and higher in summer, and, 
 probably, will not exceed 20° or 25° on an average, 
 during the time that artificial heat is required. 
 Every cubic foot of air will then absorb an additional 
 quantity of about 3^ to 4 grains of vapour ; and we 
 may therefore estimate the quantity of air which is 
 requisite to carry off the insensible perspiration, at 
 3 cubic feet, and for the pulmonary supply half a 
 cubic foot per minute, for each individual. 
 
 224. This calculation is sufficient for estimating 
 the quantity of air which in winter is required to be 
 warmed per minute, as explained Art. 151. But 
 for the purpose of summer ventilation a larger allow- 
 ance should be made. As the dew point is much 
 higher in summer, the air will absorb less moisture 
 from the body, while at the same time, the exhala- 
 tions from the body are considerably greater in 
 summer than in winter. For summer ventilation, 
 therefore, at least 5 cubic feet of air per minute, for 
 each person, ought to be changed, in order to main- 
 tain the purity of the room ; that is, 4^ cubic feet 
 
 nent of Europe, and across the dry and arid countries of the 
 Asiatic Continent, must necessarily part with much of its mois- 
 ture, acquired from the Pacific Ocean, before it reaches us ; and, 
 therefore, it will be to us a dry wind : while, on the contrary, 
 a westerly wind is always charged with a large quantity of mois- 
 ture, absorbed during its passage from the American Continent, 
 across the Atlantic. Its passage over this ocean, — a distance of 
 3000 miles, — occupies a period varying from 3 to 10 days ; dur- 
 ing which time it is constantly imbibing moisture from the 
 ocean. 
 
 N 
 
178 
 
 REMARKS ON 
 
 for tlie absorption of the insensible perspiration, and 
 lialf a cubic foot for the pulmonary transpiration. 
 
 225. Other causes of deterioration of the quality 
 of the air exist ; such as the consumption of oxygen, 
 and the elimination of extraneous gases, by the 
 burning of fires, candles, lamps, &c. : but as all gases 
 are capable of absorbing equal quantities of vapour, 
 it follows that, when air has been deteriorated by 
 these causes, so as to be less fit for respiration, it is 
 still just as capable of carrying off the vapour from 
 the surface of the body as pure air ; and, therefore, 
 no allowance needs be made for these causes of 
 vitiation. 
 
 226. When the quantity of air has been ascer- 
 tained which is necessary to be changed per minute 
 in any inhabited room or building, the next thing is 
 to estimate the proper size of the openings for the 
 emission of the vitiated and foul air, and also for the 
 admission of the fresh air which is required to supply 
 its place. 
 
 227. When an opening is made in the ceiling or 
 upper part of a room, the force which produces 
 motion in the air is the same universal law which 
 regulates the motion of falling bodies, and is pre- 
 cisely similar to the motion of water in a syphon, — 
 which has been already explained. (Art. 32.) The 
 total height from the floor of the room to the point 
 of final escape of the heated air, is the height of the 
 syphon. The force of motion is the difference of 
 
 1 
 
VENTILATION. 
 
 179 
 
 weight between this column of heated air and that 
 of a column of the external air of the same height. 
 Now air expands, when heated, of its bulk for 
 each degree of Fahrenheit ; and the velocity of mo- 
 tion is equal to the additional height which a given 
 weight of heated air must have, in order to balance 
 the same weight of cold air. Thus, suppose a room 
 1 2 feet in height, and the air 20° higher in the room 
 than the external temperature, — the air will expand 
 of its bulk, by the excess of temperature : there- 
 fore, 12^ feet of heated air will balance 12 feet of 
 air which is 20° lower in temperature. It has 
 already been explained (Art. 32), that, under such 
 circumstances, the motion of fluids is equal to the 
 velocity which a solid body would acquire, by falling 
 through a space equal to the excess of height which 
 the lighter body must have in order to balance the 
 heavier : this velocity is as the square root of 16 feet 
 is to \Q feet per second, so is the square root of the 
 given height to the velocity sought. This resolves 
 itself simply into multiplying the square root of 
 16 feet by the square root of the given height. But 
 as the acquired velocity of a gravitating body is 
 equal to twice the space it falls through in a given 
 time (Art. 32), the number thus found must be 
 doubled. In the case of the room we have before 
 supposed, as the additional height of the heated 
 column of air is 6 inches, so the square root of 
 6 inches, reduced to the decimal of a foot, multi- 
 
 N 2 
 
180 
 
 REMARKS ON 
 
 plied by the square root of 16 feet, and that product 
 multiplied by 2, will give 5*6 feet per second, as the 
 velocity of the air. An opening in the ceiling, 
 1 foot square, will therefore discharge 336 cubic 
 feet of air per minute. 
 
 228. It will be perceived that here also, as well 
 as in the case of the circulation of water (Art. 33), 
 if either the vertical height or the excess of tem- 
 perature of the room be increased fourfold, the 
 velocity will, in either case, be twice as rapid as 
 before. But whatever be the calculated velocity, 
 the real discharge will not be so great as this theo- 
 retical quantity, — not only in consequence of fric- 
 tion, but also because the air will be cooled in its 
 passage through the ventilating tubes, particularly if 
 they extend beyond the roof of the building. This 
 will considerably lessen the discharge; and we 
 ought therefore to deduct a certain amount from 
 the calculation, which, on an average, should be 
 about one fourth of the whole quantity. 
 
 229. The following Table will show the discharge 
 per minute through a ventilator 1 foot square, for 
 various heights and differences of temperature, — the 
 allowance which is above stated having here been 
 made. The discharge through a ventilator of any 
 other size may easily be calculated ; because, as the 
 area is here 144 square inches, we have only to 
 multiply the number of feet found by the Table, by 
 the number of square inches in the area of the pro- 
 
VENTILATION. 
 
 181 
 
 posed ventilator, and then, by dividing that number 
 by 144, the quotient will be the quantity sought, 
 which will represent the number of cubic feet of air 
 that will be discharged per minute by the proposed 
 ventilator. 
 
 TABLE of the Quantity of Air, in Cubic Feet, discharged per 
 Minute, through a Ventilator of which the Area is 1 square 
 Foot. 
 
 Height 
 
 Diflference between Temperature 
 
 of Room and 
 
 of 
 
 
 
 External Air. 
 
 
 
 Ventilator, 
 
 
 
 
 
 
 
 in Feet. 
 
 5° 
 
 10° 
 
 15° 
 
 20° 
 
 25° 
 
 30° 
 
 10 
 
 116 
 
 164 
 
 200 
 
 235 
 
 260 
 
 284 
 
 15 
 
 142 
 
 202 
 
 245 
 
 284 
 
 318 
 
 348 
 
 20 
 
 164 
 
 232 
 
 285 
 
 330 
 
 368 
 
 404 
 
 25 
 
 184 
 
 26 J 
 
 318 
 
 368 
 
 410 
 
 450 
 
 30 
 
 201 
 
 284 
 
 347 
 
 403 
 
 450 
 
 493 
 
 35 
 
 218 
 
 306 
 
 376 
 
 436 
 
 486 
 
 531 
 
 40 
 
 235 
 
 329 
 
 403 
 
 465 
 
 518 
 
 570 
 
 45 
 
 248 
 
 348 
 
 427 
 
 493 
 
 551 
 
 605 
 
 50 
 
 260 
 
 367 
 
 450 
 
 518 
 
 579 
 
 635 
 
 The above Table shows the discharge through a ventilator 
 of any height, and for any difference of temperature. Thus, 
 suppose the height of the ventilator, from the floor of the room 
 to the extreme point of discharge, to be 30 feet, and the differ- 
 ence between the temperature of the room and of the external air 
 to be 15°, then the discharge through a ventilator 1 foot square 
 will be 347 cubic feet 'per minute. If the height be 40 feet, and 
 the difference of temperature 20°, then the discharge will be 465 
 cubic feet per minute. 
 
 230. The height of the ventilator will, in some 
 
182 
 
 REMARKS ON 
 
 cases, be very considerably greater than the height 
 of the room. Suppose, for instance, a church is 
 required to be ventilated ; the ducts or channels 
 which carry off the heated air will probably pass for 
 a considerable height between the ceiling and the 
 roof, and will, most likely, also extend above the 
 roof. The total vertical height of all this must be 
 measured as the height of the ventilator; but, of 
 course, not taking into the account the lateral 
 length which may be given to it for the purpose of 
 uniting the several ventilators into one main trunk, 
 or for making the extreme termination at a more 
 convenient part of the roof. 
 
 231. As the discharge through any given height 
 and size of ventilator, is less in proportion as the 
 difference between the external and internal tem- 
 perature is smaller, it follows, that it will be most 
 difficult to obtain ventilation in hot weather. In 
 summer, either the number or the dimensions of the 
 ventilators should be increased; otherwise a room 
 which is well ventilated in winter, will be extremely 
 uncomfortable in summer. The increase in size can 
 be effected by having moveable ventilators, which 
 can be contracted at pleasure ; and the actual size 
 of the trunk or channel which conveys the air away, 
 should be sufficiently large to carry off the largest 
 quantity of air required for summer ventilation. 
 
 232. The openings for the admission of cold air, 
 should always be placed as near to the floor as 
 
VENTILATION. 
 
 183 
 
 possible. In size, they should be much larger than 
 the area of the ventilators, in order that the influx 
 of cold air may not proceed with too great velocity, 
 and cause a draught. In fact, the size of these 
 openings is a matter of indifference, provided only 
 that they be sufficiently large ; for the quantity of 
 air which enters through them depends entirely 
 upon the quantity that passes off through the venti- 
 lators, and not vice vei^sd : for if the passages for the 
 cold air were double the size of the ventilators, no 
 more cold air could enter, than a quantity equivalent 
 to that of the heated air which escapes at the 
 ceiling ; and none of the heated air can escape at 
 the cold air channels, because heated air cannot 
 descend. 
 
 233. The more numerous and divided are the 
 openings for the admission of cold air, the less 
 inconvenience will ; be experienced by currents : but 
 unless a sufficient quantity of cool air be admitted 
 in this manner, there will be a counter current of 
 cold air forced through the ventilators, which will 
 descend and produce a very disagreeable draught. 
 
 234. In all moderate sized buildings, this mode 
 of ventilation will be sufficient for every purpose. 
 But in buildings of very great magnitude, artificial 
 means of ventilation must be adopted, because the 
 mere difference of weight between the two columns 
 of air, will not be enough to expel the heated air 
 with sufficient velocity, particularly in hot weather. 
 
184 
 
 REMARKS ON 
 
 For theatres, this mode is generally inapplicable; 
 and it has likewise been found ineffectual for the 
 ventilation of the houses of Parliament. 
 
 235. The ventilation of the late House of Commons 
 was, for many years, a subject of complaint, and it 
 engaged the attention of many practical and scien- 
 tific men. The apparatus which has recently been 
 erected for this purpose, in the present House of 
 Commons, under the direction of Dr. Reid, for 
 producing ventilation by means of an immense 
 chimney draught, appears to be a most expensive 
 and cumbrous contrivance, for accomplishing an 
 object obtainable by far easier means. The thorough 
 ventilation of such a building as this, can only be 
 procured by two methods, — draught by heat, or 
 mechanical ventilation by a fan : but the latter of 
 these methods possesses so many advantages over 
 the former, that it appears surprising it should, for 
 so many years, have been neglected ; and that, of all 
 the numerous plans which have been tried, for 
 ventilating the late House of Commons, the draught 
 by heat, though applied in various ways, has been 
 the principle of them all. Dr. Ure has recently 
 written a valuable memoir on the subject of ventila- 
 tion, in which he compares the advantages of these 
 two methods; and he estimates the economy of 
 ventilating by a fan, compared with that by chimney 
 draught, as about 38 to I. In his calculations on 
 this subject, however, he has apparently been led 
 
VENTILATION. 
 
 185 
 
 into an error. His experiments on. the consumption 
 of fuel, to produce a given effect by chimney draught, 
 were all made on furnaces used either for steam 
 boilers, or for brewers' coppers. But, as it could 
 only be the residual heat of the furnace which 
 became available in his experiments, after the 
 principal part of the heat given off by the coal had 
 been absorbed by the boiler, it is certain that any 
 calculation, founded on the effect produced in this 
 manner, must be below the truth, as much probably 
 as a half or two-thirds. But although the relative 
 cost of fuel will not be so greatly different as 
 Dr. Ure supposes, under any circumstances the 
 difference between the two methods must be con- 
 siderable. 
 
 236. The efficiency of the mechanical method of 
 ventilation by a fan, turned by machinery, has been 
 proved so extensively in some of the largest manu- 
 factories in the kingdom, that it appears singular 
 Dr. Reid should have adopted so cumbrous and 
 expensive a contrivance as that which he has erected 
 at the present House of Commons. Whether or not 
 this method of ventilation be adopted in the new 
 Houses of Parliament, I have no doubt, that, ulti- 
 mately, the more simple, efficient, and economical 
 plan of ventilating by a fan will be resorted to. 
 
 237. As the motion of the air through tubes and 
 ventilators depends for its velocity upon the vertical 
 height of the tube only, it follows, that, if several 
 
186 
 
 REMARKS ON 
 
 ventilating tubes be used in the same room, they 
 must all be exactly of the same height ; if they are 
 not so, it frequently happens that cold air descends 
 through the lower tubes, and the highest one alone 
 conveys the heated air from the building. But the 
 horizontal length of the tube, it has already been 
 observed, makes no difference : and it is essential in 
 large buildings, when more than one ventilator is 
 necessary, either to connect the various lateral tubes 
 into one main trunk, or else to have all the various 
 tubes exactly of a similar altitude. Whether the 
 heated air merely rises by its want of gravity, or 
 whether it be drawn out of the building by means 
 of a chimney draught, as adopted by Dr. Reid in the 
 House of Commons, or exhausted mechanically by a 
 fan, this rule, respecting the vertical height being 
 the same in all the tubes, must be observed. 
 
 238. To conclude these remarks : — after what has 
 here been stated, it were unnecessary farther to 
 insist on the importance of ventilation, as regards 
 both the health and comfort of all those whose occu- 
 pations, or inclinations, confine them much within 
 doors. The important alterations which atmos- 
 pheric air undergoes in the process of breathing, 
 would alone be sufficient to establish the necessity 
 of attention to this subject. But the effects which 
 arise from this cause, are often greatly increased by 
 bad methods of warming: and these two causes 
 combined, are sufficient to produce the most exten- 
 
VENTILATION. 
 
 187 
 
 sive injury to the animal economy, when exposed to 
 their influence for any length of time. In the 
 following chapter, we shall endeavour, in following 
 out this subject, to investigate the principles of the 
 various methods of warming by artificial heat, and 
 the physiological effects which result from their 
 use. 
 
CHAPTER XIL 
 
 On the different Modes of distributing Artificial Heat — Advan- 
 tages of Radiating Heat at low Temperatures— Effects pro- 
 duced by Hot-Air Stoves in general — Nott's Stoves — Heating 
 by Flues — Dr. Arnott's Stoves — Gas Stoves — General 
 Remarks. 
 
 239. Important as are the alterations which take 
 place in atmospheric air by the process of respira- 
 tion, not less important are those produced upon it 
 by several of the methods now in use, for the 
 warming of buildings ; for the effects which result 
 from many of them are highly injurious to animal 
 life. 
 
 240. The effect produced on the animal economy 
 by atmospheric air which has passed over intensely 
 heated metallic surfaces, has already been noticed 
 (Art. 183). There are, however, other changes 
 produced on atmospheric air, by subjecting it to 
 the action of heat, which are extremely important. 
 
 241. When air passes over the heated surface of 
 a hot-air stove, the small particles of animal and 
 vegetable matter, which are always held suspended 
 
HOT-AIR STOVES. 
 
 189 
 
 in the air, are decomposed by the heat, and resolved 
 into their various elementary gases. This is one of 
 the causes of the unpleasant smell which usually 
 results from the use of such stoves. But in addition 
 to this, the hygrometric water of the atmosphere is 
 almost entirely decomposed ; the oxygen entering 
 into combination with the iron, and the hydrogen 
 mixing with the air. This alteration materially 
 affects the salubrity of the air : for not only is its 
 desiccating influence on the lungs and skin increased 
 to a most dangerous extent (Art. 218), but the 
 admixture of the disengaged hydrogen with the 
 atmospheric air, is, perhaps, even more injurious 
 than the alteration of its hygrometric state ; or, if 
 not, its effects are, at all events, sooner discovered. 
 
 242. Signer Cardone made some experiments on 
 the effects which result from the breathing of 
 hydrogen gas. He inhaled 30 cubic inches, which 
 is about one-ninth part the total capacity of the 
 lungs ; and the almost immediate effects he expe- 
 rienced were an oppressive difficulty of breathing, 
 and painful constriction at the superior orifice of 
 the stomach, followed by abundant perspiration, 
 tremor of the body, heat, nausea, and violent head- 
 ach ; his vision became indistinct, and a deep 
 murmur confused his hearing. Some of these 
 symptoms lasted a considerable time, and were 
 with difficulty got rid of. 
 
 243. The effects which are here described would 
 
190 
 
 VITIATION OF 
 
 not, of course, be so powerfully experienced with 
 the quantity of hydrogen that is disengaged by the 
 action of a hot-air stove : but neither is this quan- 
 tity so small as might be imagined, nor is it the 
 sole cause of the injury which results from the use 
 of such stoves. 
 
 244. We have already seen that the particles of 
 animal and vegetable matter, contained in the air, 
 are decomposed by the heat ; and they then produce 
 extraneous gases consisting of sulphuretted, phos- 
 phuretted, and carburetted hydrogen, with various 
 compounds of nitrogen and carbon, all of which are 
 of a character highly inimical to the animal economy. 
 The quantity of hydrogen which is eliminated by the 
 decomposition of the water contained in the air, is 
 1325 cubic inches for every cubic inch of water 
 which is decomposed ; and if the dew point of the 
 air be 45° at an average, this quantity of gas will be 
 given out from every 72 cubic feet of air which 
 passes over the heated surface of the stove. It is, 
 therefore, neither difficult to account for the ener- 
 vating effects produced by hot-air stoves, in conse- 
 quence of the air, when thus artificially dried, 
 abstracting too much moisture from the human 
 body, nor to foresee the injury which their constant 
 use must produce, when used in close rooms, by 
 breathing the extraneous gases which are evolved 
 from the decomposition of the constituent parts of 
 the atmosphere. 
 
ATMOSPHERIC AIR. 
 
 191 
 
 245. Though not usually susceptible of any diag- 
 nostic effects, I have, many times, felt sensibly 
 affected on entering rooms heated by a peculiar 
 kind of hot-air stove, which was invented by Dr. 
 Nott. The extreme heat of these stoves, produces, 
 in a very powerful degree, all the effects which are 
 above described : and perhaps no better proof needs 
 be desired, of the justice of the foregoing remarks, 
 as applied to hot-air stoves in general, than can be 
 obtained by any person standing near to one of 
 these stoves for a few minutes. The feeling of 
 oppression which is produced is intolerably painful ; 
 and the relief immediately experienced on going 
 into the fresh air, at once points out the cause of 
 the inconvenience. 
 
 246. The extreme dryness of the air, after it has 
 been deprived of its hygrometric water by passing 
 over a stove of this description, frequently produces 
 violent headach ^ ; and to remedy this evil it is 
 usual to place a vase, containing water, on the 
 stove, which, by yielding a portion of vapour to 
 the air, attempers its extreme dryness, and in some 
 degree mitigates this inconvenience. The evil, how- 
 ever, caimot be got rid of by such means ; for even 
 
 ^ This is a necessary consequence of exposure to an atmosphere 
 of excessive dryness : for the cold which is produced by the rapid 
 evaporation of moisture from the skin, contracts the capacity of 
 the absorbents, and causes the fluids to flow towards the head. 
 Tension of the brain is thus produced, with all its attendant 
 evils. 
 
192 
 
 BRICK FLUES. 
 
 if the proper quantity of moisture could be again 
 restored to the air, the effects which result from the 
 evolution of extraneous gases, would not be at all 
 removed. 
 
 247. As the power of iron to decompose water 
 increases with the temperature of the iron, the 
 limit to which the temperature of any metallic 
 surfaces ought to be raised, which are used for 
 radiating heat for the warming of buildings, should 
 not much, if at all, exceed 212°, if the preservation 
 of health is a matter of moment. The importance 
 of this rule cannot be too strongly insisted on. It 
 ought to be the fundamental principle of every 
 plan : for upon it depends the wholesomeness of 
 every system of artificial heat. 
 
 248. The various kinds of hot-air stoves, though 
 they differ considerably in their effects, are all 
 nearly similar in principle. In very large stoves, 
 the air frequently passes over a surface of iron, 
 nearly, if not quite, red hot, and is then conducted 
 through pipes, or tubes, into different parts of the 
 building which is to be warmed. This plan is 
 perhaps the most unwholesome of all ; because the 
 surface over which the air passes is generally of a 
 much higher temperature than in any of the other 
 methods. 
 
 249. The heating by means of brick flues is 
 nearly similar to the effect produced by hot-air 
 stoves. The flues are usually of a very high tem- 
 
DR. ARNOTT'S stoves. 
 
 193 
 
 peratiire, and always produce a most disagreeable 
 and unwholesome smell by the decomposition of 
 the floating particles of animal and vegetable matter 
 contained in the air; and, probably, also, by the 
 sublimation of a small portion of sulphur from the 
 substance of the bricks themselves, as well as by 
 the escape of various gases, generated during the 
 combustion of the fuel, through either the joints or 
 accidental fissures of the flues. The hygrometric 
 water of the atmosphere, however, is not decomposed 
 by this method of warming, because the materials 
 of which the flues are composed have not an aflinity 
 for oxygen such as that possessed by heated metal : 
 and in this particular flues are more wholesome 
 than hot-air stoves. 
 
 250. A new kind of hot-air stove has lately been 
 invented by Dr. Arnott, which is intended to obviate 
 the bad effects resulting from those of the usual 
 construction. This stove consists of an oblong case, 
 or box, of wrought iron, about 3 feet long, 2 feet 
 wide, and 2 feet high. It is divided across the 
 middle by a partition which separates it into two 
 distinct compartments, communicating with each 
 other by small openings at top and bottom. The 
 fire is contained in a fire-clay basket, which is placed 
 in the first compartment, and the only air admitted 
 is through a small circular hole at the side ; the 
 door in the front, for supplying fuel, being made to 
 flt as close and as nearly air-tight as possible. A 
 
 o 
 
194 
 
 DR. ARNOTT'S stoves. 
 
 metal cover, attached to a series of expanding plates, 
 closes this hole : when the heat of the stove becomes 
 too great, the plates, by their expansion, draw the 
 cover, which closes the hole, inwards ; thus shutting 
 off the communication of the air, wholly or partially, 
 according as the temperature acts with greater or 
 less force on the expanding plates. On closing the 
 opening in this manner, the fire immediately slackens 
 for want of sufficient air to support combustion of 
 the fuel ; and the temperature of the stove decreas- 
 ing, the plates inside again collapse, and thus admit 
 more air to the fire : the combustion can therefore 
 be regulated so as to keep the stove at almost any 
 temperature. The air circulates within the two 
 chambers by the small openings which connect them, 
 but the room is warmed by the air passing over the 
 surface of the stove only. The smoke escapes 
 through a flue, in the usual manner ; and as the fire 
 never comes in contact with the surface of the stove, 
 every part of it is kept at a low temperature, — about 
 200° of Fahrenheit. 
 
 251. The temperature of this stove being so low, 
 no injurious effects are produced, as in other stoves, 
 by decomposing the vapour and the particles of 
 matter which are suspended in the air: but as a 
 large quantity of carbonic oxide is generated by coke 
 in a low state of combustion, there is a tendency for 
 this deleterious gas to escape into the room, in con- 
 sequence of the draught of the chimney being so 
 
DR. ARNOTT'S stoves. 
 
 195 
 
 small, that it barely causes its withdrawal from the 
 stove \ 
 
 252. The heat afforded by this stove is so incon- 
 siderable as to render it inapplicable, except in 
 rooms of small size. The large dimensions of the 
 stove is also an inconvenience ; and if its size be 
 reduced, the effect is also decreased in the same pro- 
 portion, which must therefore prevent its use, except 
 in a very limited degree. 
 
 253. The efficacy and advantages of any invention 
 for warming, do not, however, simply consist in the 
 fact, that the apparatus employed will not decom- 
 pose the vapour contained in the atmosphere, or 
 eliminate any permanently elastic gases ; for if, on 
 the contrary, a moist heat were produced, its influ- 
 ence on the human organization would be not less 
 injurious than we have shown results from an oppo- 
 site condition of the atmosphere. 
 
 254. As the air is only able to contain a definite 
 quantity of vapour (Chapter XI.), by adopting any 
 method of artificial heat which evolves an excess of 
 
 * This objection also lies against all stoves, which have a very 
 slow draught. The effects produced by the breathing of this gas 
 are extremely prejudicial to the animal economy. Sir H. Davy, 
 on trying the effects of inhaling a small quantity of it, was seized 
 with a temporary loss of sensation, succeeded by giddiness, sick- 
 ness, and acute pains in different parts of his body ; and it was 
 some days before he entirely recovered. But Mr. Witter, of 
 Dublin, who tried to repeat the experiments, was immediately 
 affected with apoplexy, and was restored with difficulty. 
 
 o 2 
 
196 
 
 GAS STOVES. 
 
 moisture, the natural exhalations from the lungs and 
 skin cannot be carried off. and pulmonary consump- 
 tion must ultimately be induced, provided the con- 
 tinuance of the exciting cause be of sufficient dura- 
 tion. A notable instance of this kind of heat is 
 that which is produced by the " gas stove," an inven- 
 tion by which the burning of carburetted hydrogen 
 gas is employed as a substitute for coal. The effects 
 of this plan are, however, very prejudicial to the 
 human frame, for the whole of the gas consumed in 
 these stoves is converted into two new compounds, 
 water and carbonic acid gas, — which are both exhaled 
 into the air of the room. The quantity of water, in 
 the form of vapour, distributed by one of these stoves, 
 is very considerable, for each cubic foot of carbu- 
 retted hydrogen gas w^hich is consumed, produces 2*6 
 cubic inches of water ; and as the consumption of 
 gas, in a moderate-sized stove of this description, is 
 from 12 to 15 cubic feet per hour, the total quan- 
 tity of water given off to the air, will be from a pint 
 to a pint and a quarter per hour. 
 
 255. The large quantity of oxygen gas, which is 
 abstracted from the air to support the flame of the 
 carburetted hydrogen, would not of itself be of much 
 consequence, provided the nitrogen, which is by this 
 means set free, could escape, as it does in other 
 stoves, without mixing with the air of the room. 
 But, in consequence of these stoves having no flues, 
 
GAS STOVES. 
 
 197 
 
 the whole of the nitrogen or azotic gas \ which is 
 eliminated from the atmosphere, amounting to eight 
 times the quantity of hydrogen consumed, or about 
 100 to 120 cubic feet per hour, together with about 
 12 or 15 cubic feet of carbonic acid gas, mixes with 
 the air in the room, and must be breathed by the 
 inmates, there being no outlet by which it can 
 escape. 
 
 256. The plan which has recently been tried of 
 introducing flues into these stoves, in order to carry 
 off the unwholesome products of the combustion, 
 would be a very great improvement, were it not that 
 in carrying off the extraneous gases and the steam, 
 the heat received in the room, is, at the same time, 
 so much reduced, as to render the stoves compara- 
 tively valueless, as regards their heating effect. If 
 the whole of the water, which is formed by a stove 
 burning for 15 hours, at the rate of 15 cubic feet of 
 gas per hour, escapes uncondensed in the state of 
 steam, which is the form it assumes before it be- 
 comes water ; as much heat will be carried off, as 
 would, had the steam been condensed at the tem- 
 perature of 60°, have heated 1 16,790 cubic feet of 
 air 10°. To this must be added, the loss from the 
 heated air that escapes through the flue, which is 
 probably about as much more ; and, together, the 
 
 ^ The name of azote (derived from two Greek words, signifying 
 without life,) was given to this gas, on account of its peculiarly 
 fatal effects on animal life. 
 
198 
 
 GAS STOVES. 
 
 amount thus lost is nearly one-half the heat which 
 the stove affords under the most favourable circum- 
 stances. This may be proved by the following cal- 
 culation, showing at the same time, the relative cost 
 of warming by gas and by coal. 
 
 257. The experiments of Dr. Dalton have proved 
 that by the combustion of one pound in weight of 
 carburetted hydrogen gas, as much heat is generated 
 as will melt 85 lbs. of ice. Now, a cubic foot of car- 
 buretted hydrogen weighs 292*89 grains, and, in a 
 stove burning 15 cubic feet an hour, for 15 hours a 
 day, there will be 225 cubic feet, or 9*4 1 lbs. of gas 
 consumed, which would, therefore, melt 799 lbs. of 
 ice; and the cost of this quantity of gas, at the usual 
 average price, would be two shillings and threepence. 
 The latent heat of water being 140°, it requires as 
 much heat to melt 1 lb. of ice, and to raise its temper- 
 ature from 32° to 33°, as would raise the temperature 
 of the same weight of water 141°; and as the cubic 
 foot of water weighs 62*33 lbs., therefore, the same 
 quantity of heat that would melt 799 lbs. of ice 
 would heat 12*8 cubic feet of water 140°^ or 179.2 
 cubic feet 10°. By referring to Art. 140, we shall 
 find that 1 cubic foot of water will raise the tem- 
 perature of 2990 cubic feet of air as many degrees 
 as the water loses ; and the combustion of 225 cubic 
 feet of carburetted hydrogen gas would therefore 
 raise the temperature of 535,808 cubic feet of air 
 10°. The quantity of coal which will produce the 
 
GAS STOVES. 
 
 199 
 
 same effect is easily ascertained. By Art. 138, we 
 find that 1 lb. of coal will heat 39 lbs. of water 180°, 
 or 702 lbs. of water 10°. This is equal to 11,170 
 lbs., or 179*20 cubic feet of water being heated 10° 
 by 15*91 lbs. of coal : and this number of cubic feet 
 of water multiplied by 2990 (Art. 140), will give 
 535,808 cubic feet, as the quantity of air that would 
 be heated 10° by 15*91 lbs. of coal, which is exactly 
 the same result as is obtained by the combustion of 
 225 cubic feet of carburetted hydrogen gas. The 
 only difference would be that the gas would cost 
 2s. 3(/., and the coal no more than 3g?., or, to allow 
 for extra expenditure of fuel, from imperfect con- 
 struction of the stove, say the coal will cost 5g?. ; so 
 that a gas stove, without a flue, will cost about five 
 times as much for fuel, as a hot-air stove which 
 burns coal, and about ten times as much as coal, if 
 the gas stove has a flue ^ 
 
 258. It requires no deep researches into the prin- 
 cijjles of physiology, to appreciate, in some degree, at 
 least, the merits of a niethod of artificial heat, which 
 is free from all the noxious effects which we have 
 seen result from the use of most of the inventions 
 that have been described. Although many persons 
 
 ^ This latter amount may be reduced by making the flue of the 
 stove very long and very large in diameter, so as to condense the 
 steam by exposing to it a large surface. This would save a con- 
 siderable portion of heat, but the form and size of the flue would 
 probably be very inconvenient. 
 
200 
 
 PHYSIOLOGICAL EFFECTS. 
 
 are not aware of the full extent of the injury that 
 results from these causes, the merest sciolist in the 
 investigation of natural phenomena must acknow- 
 ledge, that the more we deviate from the simplicity of 
 Nature's laws, the more fatal are the effects on that 
 most delicate of all her works — organic life. And it 
 needs no farther arguments to prove that it must be 
 injurious to breathe an atmosphere contaminated 
 by extraneous gases, which have not the power of 
 supporting animal life, or that extracting from the 
 air its natural humidity, or, on the contrary, loading 
 it with vast quantities of moisture, must produce 
 consequences inimical to the health of organized 
 beings. 
 
 259. Nor is it only to animal life that these 
 results ensue. It is equally on all departments of 
 organized existence, in the vegetable as well as the 
 animal kingdom, that the injurious effects of erro- 
 neous principles of warming exert their influence ; 
 for it will readily be conceded that we cannot violate 
 the one class of laws with impunity, any more than 
 we can the other. It is therefore only conformable 
 to what might be anticipated, that practical gar- 
 deners have almost universally acknowledged the 
 superior healthiness and productiveness of plants 
 cultivated in houses which are warmed by the circu- 
 lation of hot water. 
 
 260. The perfect freedom from all these noxious 
 effects which have been described, is not the least 
 
PHYSIOLOGICAL EFFECTS. 
 
 201 
 
 important of the advantages afforded by this method 
 of distributing artificial heat. It would, however, 
 be attended with disadvantages of a formidable cha- 
 racter, if it were applied to any inhabited rooms 
 which are not supplied with proper ventilation. 
 In a room warmed by stoves of the common con- 
 struction, the open fire-place itself affords sufficient 
 ventilation in ordinary cases ; but with all other 
 modes of warming, ventilation must be supplied, if 
 it be wished to avoid the evils resulting to the 
 human frame, from breathing a vitiated atmosphere, 
 whether it be rendered impure by having passed 
 through the lungs, or in consequence of extraneous 
 gases either generated or evolved by peculiar me- 
 thods of warming. 
 
 261. This remark would have been superfluous, 
 were it not that cases have occurred where the evils 
 that have arisen from defective ventilation have 
 been erroneously attributed to this plan of warming 
 by hot water ; and the vapour which is given off from 
 the lungs of the inmates of a room, and, under these 
 circumstances, is condensed upon the windows, has 
 been supposed to arise from the water in the appa- 
 ratus being converted into steam, and escaping 
 through the joints of the pipes. If this were a 
 solitary opinion, it might, like many others equally 
 erroneous, merely excite a smile from those who are 
 better acquainted with the subject ; but as this has 
 been seriously objected against the invention, by 
 
202 
 
 DEPOSITION OF VAPOUR 
 
 many who ought to know better, it may be worth 
 while to state the cause more at length. 
 
 262. The quantity of vapour given off from the 
 lungs, and also by exhalation from the skin, has 
 been estimated at from 12 to 13 grains per minute. 
 If, in consequence of imperfect ventilation of inha- 
 bited rooms, the air cannot escape after it has 
 received this additional quantity of vapour exhaled 
 from the body, it must, as soon as it has acquired a 
 larger quantity of moisture than the temperature of 
 the eternal air will support in the form of vapour 
 (Art. 219), deposit a portion of it upon the glass; 
 because, the glass being nearly of the same tempera- 
 ture as the external air, whatever quantity of the 
 internal air comes in contact with it, its temperature 
 is immediately lowered, and the excess of its vapour 
 is condensed upon the surface of the glass. Thus, 
 suppose the temperature of the air in a room to be 
 65°, and the dew point 55°, then, if the temperature 
 of the external air be only 35°, as much of the air 
 in the room as comes in contact with the glass, will 
 deposit whatever vapour it contains above the quan- 
 tity that a temperature of 35° will enable it to sus- 
 tain. Under these circumstances, the amount 
 deposited on the glass will be (Art. 219) about 
 2 grains for each cubic foot of air that is cooled by 
 the glass ; and the same effect, though in a less 
 degree, will take place on all the other cold surfaces 
 in the room. As each square foot of glass will cool 
 
 1 
 
ON WINDOWS. 
 
 203 
 
 one and a quarter cubic feet of air per minute, from 
 the internal to the external temperature (Art. 145), 
 we shall find that, under the circumstances we have 
 supposed, — which is purposely taken as an extreme 
 case, — the quantity of vapour deposited in this man- 
 ner will amount to 2^ grains per minute, on each 
 square foot of glass. 
 
 263. We need be at no loss, then, to discover the 
 cause of this accumulation of vapour on the windows 
 and walls of rooms which are badly ventilated ; and 
 whenever the quantity of moisture thus condensed 
 appears to be considerable, it may be taken as good 
 evidence that the ventilation of the room is imper- 
 fect. That the same effect does not result from the 
 use of hot-air stoves, is in consequence of the 
 vapour being decomposed by the intense heat ; but 
 when this method of avoiding the inconvenience is 
 adopted, a worse evil is produced than that which is 
 attempted to be removed, although, perhaps, it is 
 not so obvious to the sight. 
 
 264. Some of the preceding remarks have ex- 
 tended to a greater length, and have assumed a 
 more prominent place, than was intended ; but it 
 may not, perhaps, be deemed altogether super- 
 fluous, in concluding this Treatise, to observe, that 
 the investigation of the physiological effects of the 
 different systems of artificial heat, is not only inte- 
 resting in a scientific point of view to the physiolo- 
 gist, but it closely concerns almost every individual 
 
204 
 
 CONCLUDING REMARKS. 
 
 member of the community. It is a question which 
 affects not merely the personal comfort of indivi- 
 duals, but, according to the opinion of some of our 
 ablest pathologists, it influences the health, and even 
 affects the duration of life. Such a subject, then, 
 cannot but be deserving of investigation: and if 
 these observations, imperfect as they are, have the 
 effect of directing more general attention to the 
 inquiry, they will not have been made in vain. 
 
205 
 
 TABLE I. 
 
 TABLE of the Expansive Force of Steam, in Atmospheres, and 
 in lbs. per square inch; for temperatures above 212° of 
 Fahrenheit. 
 
 N.B. The steam is supposed to be in contact with the water from which it is 
 formed, and the water and steam to be alike in temperature. 
 
 rees 
 ?it. 
 
 Pressure. 
 
 CO 
 
 Pressure. 
 
 rees 
 
 Pressure. 
 
 Q § 
 
 )spheres. 
 
 lbs. 
 
 It in Deg 
 Fahrenht 
 
 )spheres. 
 
 lbs. 
 
 It in Deg 
 Fahrenh( 
 
 )spheres. 
 
 lbs. 
 
 w ° 
 
 Atm( 
 
 
 w 
 
 Atmc 
 
 
 a> 
 
 Atmc 
 
 
 212 
 
 1 
 
 15 
 
 431 
 
 23 
 
 345 
 
 646 
 
 150 
 
 2250 
 
 251 
 
 2 
 
 30 
 
 436 
 
 24 
 
 360 
 
 655 
 
 160 
 
 2400 
 
 275 
 
 3 
 
 45 
 
 439 
 
 25 
 
 375 
 
 663 
 
 170 
 
 2550 
 
 294 
 
 4 
 
 60 
 
 457 
 
 30 
 
 450 
 
 671 
 
 180 
 
 2700 
 
 308 
 
 5 
 
 75 
 
 473 
 
 35 
 
 525 
 
 679 
 
 190 
 
 2850 
 
 320 
 
 6 
 
 90 
 
 487 
 
 40 
 
 600 
 
 686 
 
 200 
 
 3000 
 
 332 
 
 7 
 
 105 
 
 499 
 
 45 
 
 675 
 
 694 
 
 210 
 
 3150 
 
 342 
 
 8 
 
 120 
 
 511 
 
 50 
 
 750 
 
 700 
 
 220 
 
 3300 
 
 351 
 
 9 
 
 135 
 
 521 
 
 55 
 
 825 
 
 707 
 
 230 
 
 3450 
 
 359 
 
 10 
 
 150 
 
 531 
 
 60 
 
 900 
 
 713 
 
 240 
 
 3600 
 
 367 
 
 11 
 
 165 
 
 540 
 
 65 
 
 975 
 
 719 
 
 250 
 
 3750 
 
 374 
 
 12 
 
 180 
 
 549 
 
 70 
 
 1050 
 
 726 
 
 260 
 
 3900 
 
 381 
 
 13 
 
 195 
 
 557 
 
 75 
 
 1125 
 
 731 
 
 270 
 
 4050 
 
 387 
 
 14 
 
 210 
 
 565 
 
 80 
 
 1200 
 
 737 
 
 280 
 
 4200 
 
 393 
 
 15 
 
 225 
 
 572 
 
 85 
 
 1275 
 
 742 
 
 290 
 
 4350 
 
 399 
 
 16 
 
 240 
 
 579 
 
 90 
 
 1350 
 
 748 
 
 300 
 
 4500 
 
 404 
 
 17 
 
 255 
 
 586 
 
 95 
 
 1425 
 
 753 
 
 310 
 
 4650 
 
 409 
 
 18 
 
 270 
 
 592 
 
 100 
 
 1500 
 
 758 
 
 320 
 
 4800 
 
 414 
 
 19 
 
 285 
 
 605 
 
 110 
 
 1650 
 
 763 
 
 330 
 
 4950 
 
 418 
 
 20 
 
 300 
 
 616 
 
 120 
 
 1800 
 
 768 
 
 340 
 
 5100 
 
 423 
 
 21 
 
 315 
 
 627 
 
 130 
 
 1950 
 
 772 
 
 350 
 
 5250 
 
 427 
 
 22 
 
 330 
 
 636 
 
 140 
 
 2100 
 
 
 
 
 The above Table is deduced from the experiments of M. M. 
 Dulong and Arago. Their calculations extend only as far as 50 
 atmospheres ; from thence the pressures are now calculated to 
 350 atmospheres by their formula, viz. : — 
 t =s/e-\ 
 •7153 
 
 where e represents the pressure in atmospheres, and t the tem- 
 
206 
 
 perature above 100° of Centigrade. In this equation each 100° 
 of Centigrade is represented by unity. 
 
 In reducing these temperatures from Centigrade to Fahrenheit's 
 scale, where the fractions amount to '5, they have been taken as 
 the next degree above, and all fractions below '5 have been 
 rejected. 
 
 TABLE IT. 
 
 TABLE of the Quantity of Vapour contained in Atmospheric 
 Air, at different Temperatures, when saturated. 
 
 Temperature of Air. 
 
 Quantity of Vapour per 
 Cubic Foot : in Grains 
 Weight. 
 
 Temperature of Air. 
 
 Quantity of Vapour per 
 Cubic Foot: in Grains 
 Weight. 
 
 Temperature of Air. 
 
 Quantity of Vapour per 
 Cubic Foot : in Grains 
 Weight. 
 
 20° 
 
 1-52 
 
 48° 
 
 3-98 
 
 76° 
 
 9-53 
 
 22 
 
 1-64 
 
 50 
 
 4-24 
 
 78 
 
 10-16 
 
 24 
 
 1-76 
 
 52 
 
 4-52 
 
 80 
 
 10-78 
 
 26 
 
 1-90 
 
 54 
 
 4'82 
 
 82 
 
 11-49 
 
 28 
 
 2-03 
 
 56 
 
 5-13 
 
 84 
 
 12-20 
 
 30 
 
 2*25 
 
 58 
 
 5-51 
 
 86 
 
 12-91 
 
 32 
 
 2-32 
 
 60 
 
 5-83 
 
 88 
 
 13-61 
 
 34 
 
 2-48 
 
 62 
 
 6-21 
 
 90 
 
 14-42 
 
 36 
 
 2-64 
 
 64 
 
 6-60 
 
 92 
 
 15-22 
 
 38 
 
 2-82 
 
 66 
 
 7-00 
 
 94 
 
 16-11 
 
 40 
 
 3-02 
 
 68 
 
 7-43 
 
 96 
 
 17-11 
 
 42 
 
 3-24 
 
 70 
 
 7-90 
 
 98 
 
 18-20 
 
 44 
 
 3-48 
 
 72 
 
 8-40 
 
 100 
 
 19-39 
 
 46 
 
 3-73 
 
 74 
 
 8-95 
 
 
 
 The above Table is computed from Dr. Dal ton's Experi- 
 ments on the Elastic Force of Vapour. 
 
207 
 
 TABLE III. 
 
 TABLE of the Expansion of Air and other Gases by Heat, 
 when perfectly free from Vapour. 
 
 Temperature, 
 Fahrenheit's 
 Scale. 
 
 Expansion. 
 
 Temperature, 
 Fahrenheit's 
 Scale. 
 
 Expansion. 
 
 32° 
 
 1000 
 
 100° 
 
 1152 
 
 35 
 
 1007 
 
 110 
 
 1178 
 
 40 
 
 1021 
 
 120 
 
 1194 
 
 45 
 
 1032 
 
 130 
 
 1215 
 
 50 
 
 1043 
 
 140 
 
 1235 
 
 55 
 
 1055 
 
 150 
 
 1255 
 
 60 
 
 1066 
 
 160 
 
 1275 
 
 65 
 
 1077 
 
 170 
 
 1295 
 
 70 
 
 1089 
 
 180 
 
 1315 
 
 75 
 
 1099 
 
 190 
 
 1334 
 
 80 
 
 1110 
 
 200 
 
 1354 
 
 85 
 
 1121 
 
 210 
 
 1372 
 
 90 
 
 1132 
 
 212 
 
 1376 
 
 95 
 
 1142 
 
 
 
 The above numbers are obtained from Dr. Dalton's 
 experiments, which give an average of part, or "00207 for 
 the expansion by each degree of Fahrenheit. Gay Lussac found 
 it to be equal to part, or '002083 for each degree of Fahren- 
 heit ; and that the same law extends to condensable vapours when 
 excluded from contact of the liquids which produce them. 
 
208 
 
 TABLE IV. 
 
 TABLE of the Specific Gravity and Expansion of Water 
 at different Temperatures. 
 
 S-j . 
 
 c 
 
 o 
 
 
 Weight 
 
 ture, 
 eit's 
 
 c 
 .2 
 
 
 Weight 
 
 Is ~ .3 
 >j c w 
 
 c 
 
 Specific 
 
 of 
 
 
 -« 
 
 Specific 
 
 of 
 
 
 
 
 1 Cubic 
 
 
 cS 
 
 1 Cubic 
 
 
 
 Gravity. 
 
 Inch, 
 
 el 
 
 X 
 
 Gravity. 
 
 Inch, 
 
 Eh ^ 
 
 
 in Grains. 
 
 
 
 in Grains. 
 
 30° 
 
 •00017 
 
 •9998 
 
 252714 
 
 121° 
 
 •01236 
 
 -9878 
 
 249-677 
 
 32 
 
 •00010 
 
 •9999 
 
 252-734 
 
 124 
 
 •01319 
 
 •9870 
 
 249 473 
 
 34 
 
 •00005 
 
 •9999 
 
 252^745 
 
 
 •01403 
 
 •9861 
 
 249-265 
 
 36 
 
 •00004 
 
 •9999 
 
 252-753 
 
 130 
 
 •01490 
 
 •9853 
 
 249053 
 
 38 
 
 •000002 
 
 •9999 
 
 252*758 
 
 133 
 
 •01578 
 
 •9844 
 
 248 836 
 
 39 
 
 •00000 
 
 10000 
 
 252-759 
 
 136 
 
 •01668 
 
 •9836 
 
 248-615 
 
 43 
 
 •00003 
 
 •9999 
 
 252750 
 
 139 
 
 •01760 
 
 •9827 
 
 248-391 
 
 46 
 
 •00010 
 
 •9999 
 
 252734 
 
 142 
 
 •01853 
 
 •9818 
 
 248-163 
 
 49 
 
 •00021 
 
 •9997 
 
 252704 
 
 145 
 
 •01947 
 
 •9809 
 
 247 931 
 
 52 
 
 •00036 
 
 •9996 
 
 252 667 
 
 148 
 
 •02043 
 
 •9799 
 
 247 697 
 
 55 
 
 •00054 
 
 •9994 
 
 252 621 
 
 151 
 
 •02141 
 
 •9790 
 
 247-459 
 
 58 
 
 •00076 
 
 •9992 
 
 252-566 
 
 154 
 
 •02240 
 
 •9780 
 
 247219 
 
 61 
 
 •00101 
 
 •9989 
 
 252502 
 
 157 
 
 •02340 
 
 •9771 
 
 246-976 
 
 64 
 
 •00130 
 
 •9986 
 
 252 429 
 
 160 
 
 •02441 
 
 •9760 
 
 246-707 
 
 67 
 
 •00163 
 
 •9983 
 
 252-349 
 
 163 
 
 •02543 
 
 •9751 
 
 246-483 
 
 70 
 
 •00198 
 
 •9981 
 
 252-285 
 
 166 
 
 •02647 
 
 -9741 
 
 246-233 
 
 73 
 
 •00237 
 
 •9976 
 
 252 162 
 
 169 
 
 •02751 
 
 •9731 
 
 245 982 
 
 76 
 
 •00278 
 
 •9972 
 
 252 058 
 
 172 
 
 •02856 
 
 •9721 
 
 245 729 
 
 79 
 
 •00323 
 
 •9967 
 
 251-945 
 
 175 
 
 -02962 
 
 •9711 
 
 245-474 
 
 82 
 
 •00371 
 
 •9963 
 
 251-825 
 
 178 
 
 •03068 
 
 -9701 
 
 245 218 
 
 85 
 
 •00422 
 
 •9958 
 
 251^698 
 
 181 
 
 •03176 
 
 •9691 
 
 244962 
 
 88 
 
 •00476 
 
 •9952 
 
 251 -564 
 
 184 
 
 •03284 
 
 •9681 
 
 244 704 
 
 91 
 
 •00533 
 
 •9947 
 
 251-422 
 
 187 
 
 •03392 
 
 •9671 
 
 244 446 
 
 94 
 
 .00592 
 
 •9941 
 
 251-275 
 
 190 
 
 •03501 
 
 •9660 
 
 244 187 
 
 97 
 
 •00654 
 
 •9935 
 
 251121 
 
 193 
 
 •03610 
 
 •9650 
 
 243^928 
 
 100 
 
 •00718 
 
 •9928 
 
 250960 
 
 196 
 
 •03720 
 
 •9640 
 
 243-669 
 
 103 
 
 •00785 
 
 •9922 
 
 250-794 
 
 199 
 
 •03829 
 
 •9630 
 
 243410 
 
 106 
 
 •00855 
 
 •9915 
 
 250621 
 
 202 
 
 •03939 
 
 •9619 
 
 243 151 
 
 109 
 
 •00927 
 
 •9908 
 
 250-443 
 
 205 
 
 •04049 
 
 •9609 
 
 242893 
 
 112 
 
 •01001 
 
 •9901 
 
 250259 
 
 208 
 
 •04159 
 
 •9599 
 
 242-635 
 
 115 
 
 •01077 
 
 •9893 
 
 250070 
 
 212 
 
 •04306 
 
 -9585 
 
 242 293 
 
 118 
 
 •01156 
 
 •9885 
 
 249^876 
 
 
 
 
 
 In the above Table the expansions are calculated by Dr. 
 Young's formula, 22/^ (1--002/) in 10 millionths. The 
 diminution of specific gravity is calculated by this equation : 
 •0000022/2 _ -00000000472 In both equations, / repre- 
 sents the number of degrees above or below 39° of Fahrenheit. 
 The absolute weight of a cubic inch of water, at any temperature, 
 may be found by multiplying the weight of a cubic inch at 39°, 
 by the specific gravity at the required temperature. 
 
209 
 
 TABLE V. 
 
 TABLE of the Specific Heat, Specific Gravity, and Expansion 
 by Heat of different Bodies. 
 Barometer 30 Inches. — Thermometer 60°. 
 
 Air (atmospheric) . . 
 — (dry) .... Apjohn 
 Aqueous vapour .... 
 
 Azote 
 
 — oxide of 
 
 Carbonic acid 
 
 — oxide 
 
 Hydrogen. . 
 Olefiant gas 
 Oxygen . . . . 
 Water . . . . 
 
 Water. . 
 Bismuth 
 Brass . . . 
 
 — wire 
 
 Cobalt 
 
 Copper 
 
 Gold 
 
 Glass (flint) 
 
 (tube) 
 
 Iron (cast) 
 
 (bar) 
 
 Lead 
 
 Nickel 
 
 Pewter (fine) 
 
 Platinum . , 
 
 Silver 
 
 Solder (lead 2 -j- tin 1) . 
 Spelter (brass 2-|- zinc 1) 
 Sreel (untempered) . . . 
 
 (yellow tempered) 
 
 Sulphur 
 
 Tellurium 
 
 Tin 
 
 Zinc 
 
 Specific Heat. 
 
 •2669 
 •2767 
 •8470 
 •2754 
 •2369 
 •2210 
 •2884 
 
 3-2936 
 •4207 
 •2361 
 
 1000 
 
 S 5 
 
 1000 
 •0288 
 
 •1498 
 •0949 
 •0298 
 
 •1100 
 •0293 
 •1035 
 
 •0314 
 •0557 
 
 •1880 
 •0912 
 •0514 
 ■0927 
 
 Specific 
 Gravity. 
 
 1000 
 
 •633 
 •9722 
 1-5277 
 1-5277 
 •9722 
 •0694 
 •9722 
 11111 
 
 Weight of 
 100 Cubic 
 Inches. 
 
 OJ o 
 
 % a 
 s s 
 
 1000 
 
 9-880 
 
 7- 824 
 
 8 - .396 
 8 600 
 8-900 
 
 19-250 
 2-760 
 2^520 
 7-248 
 7-788 
 
 11-350 
 8 279 
 
 21 470 
 10470 
 
 7-840 
 7816 
 1-990 
 
 6- 115 
 
 7- 291 
 7-191 
 
 Grains. 
 30519 
 
 19-321* 
 
 29-65 
 46-596 
 46-596 
 29-65 
 
 21 18 
 29-65 
 33 888 
 
 Ounces. 
 
 57-87 
 571-7 
 452-77 
 485^87 
 497-6 
 515-0 
 1114-0 
 159-72 
 145-83 
 418-9 
 4502 
 656-8 
 478-5 
 
 1242-4 
 605-8 
 
 453-7 
 
 452-31 
 
 115-1 
 
 3535 
 421-9 
 4160 
 
 Linear Expansion 
 by 180° of Heat, 
 from 32° to 212°. 
 
 00186671 
 00193000 
 
 00172244 
 ■00146606 
 00081166 
 •00087572 
 00111111 
 00122045 
 ■00284836 
 
 ■00228.300 
 •00099180 
 00208260 
 •00250800 
 00205800 
 •00107875 
 •00136900 
 
 •00217298 
 -00294200 
 
 — 6SI 
 
 ?38 
 
 TooS 
 
 *,* Air is taken as the standard for the specific gravity of the gases, and 
 water as the standard for the solids. 
 
 * Specific gravity of steam at 212°=-481. Weightof 100 cubic inches, 14-680 grains. 
 
210 
 
 TABLE VI. 
 
 TABLE of the Effects of Heat. 
 
 Wedgwood's 
 Scale. 
 
 Greatest heat observed .... 
 Hessian crucible fused .... 
 Cast iron thoroughly melted 
 Greatest heat of a smith's forge . . 
 Ditto of a plate-glass furnace 
 Ditto of a flint glass ditto . 
 Derby porcelain vitrifies .... 
 Welding heat of iron (greatest) . 
 
 Ditto ditto (least) . . . 
 
 Fine gold melts 
 
 Fine silver melts 
 
 Swedish copper melts 
 
 Brass melts 
 
 Diamond burns 
 
 Red heat fully visible in day light . 
 Iron red-hot in the twilight 
 
 Charcoal burns 
 
 Heat of a common fire 
 
 Iron bright-red in the dark 
 
 Zinc melts (680° Davy) • . 
 
 Mercury boils (Black 600°) (Secondat 644°) (Petit 
 
 and Dulong) 
 
 (Crichton 655°)(Irvine 672°) (Dalton) 
 
 Lowest ignition of iron in the dark 
 
 Lead melts (Guyton and Irvine 594°) (Crichton) . 
 Steel becomes dark blue, verging on black . . 
 
 Ditto a full blue 
 
 Sulphur burns 
 
 Steel becomes bright blue 
 
 Ditto purple 
 
 Ditto brown, with purple spots .... 
 
 Ditto brown 
 
 Bismuth melts 
 
 Steel becomes a full yellow . 
 
 Ditto a pale straw colour 
 
 Tin melts 
 
 Steel becomes very faint yellow ...... 
 
 Tin 3 + lead 2 -f- bismuth 1, melts .... 
 
 Tin and bismuth, equal parts, melts 
 
 Bismuth 5 -f tin 3 + lead 2, melts 
 
Table of the Effects of Heat [continued). 
 
 Water boils (barometer 30 in.) . . 
 
 Water freezes 
 
 Milk freezes 
 
 Vinegar freezes 
 
 Sea water freezes 
 
 Strong wine freezes 
 
 Quicksilver congeals 
 
 Sulphuric aether congeals . . . . 
 Natural temperature at Hudson's Bay 
 Great artificial cold 
 
 TABLE VII. 
 
 TABLE of the Quantity of Water contained in 100 Feet of 
 Pipe, of different diameters. 
 
 Diameter 
 of Pipe. 
 
 Contents of 100 Feet 
 in length. 
 
 Inches. 
 
 Gallons. 
 
 1 
 
 2 
 
 •84 
 
 1 
 
 3-39 
 
 li 
 
 7-64 
 
 2 
 
 13-58 
 
 
 21-22 
 
 3 
 
 30-56 
 
 4 
 
 54-33 
 
 5 
 
 84-90 
 
 6 
 
 122-26 
 
212 
 
 TABLE VIII. 
 
 TABLE of the Strength, or Cohesive Force, of different 
 Substances : By Geo. Rennie. 
 
 Bars of 6 inches long and a J of an inch square will break with 
 the following weights suspended lengthways: — 
 
 lbs. 
 
 Cast Iron (horizontal) 1166 
 
 Ditto (vertical) 1218 
 
 Cast Steel (tilted) 8391 
 
 Blistered Steel (hammered) . . . 8322 
 
 Shear Steel (ditto) .... 7977 
 
 Swedish Iron 4o04 
 
 English Iron 3492 
 
 Hard Gun-metal 2273 
 
 Wrought Copper (hammered) . . . 2112 
 
 Cast Copper 1192 
 
 Fine Yellow Brass 1123 
 
 Cast Tin 296 
 
 Cast Lead 114 
 
 *^* A round bar of best English Iron, one-inch diameter, when 
 subjected to a longitudinal strain, will break with a weight of 
 43,520 lbs., or rather less than 19j tons. This agrees very 
 nearly with the amount above stated. 
 
 TABLE of the Relative Cohesive Strength of Metals : 
 
 By SiCKENGER. 
 
 Gold .... 150,955 
 
 Silver .... 190,771 
 
 Platinum . . . 262,361 
 
 Copper .... 304,696 
 
 Soft Iron . . • 362,927 
 
 Hard Iron . . . 559,880 
 
INDEX. 
 
 PAGE 
 
 Air, admission of in furnaces 77 
 
 — conducting power of, for heat 83 
 
 — dry, effect of on the human body 191 
 
 — eifects produced on, by heated metals 189 
 
 — loss of heat by contact with 86 
 
 — quantity of, to be warmed in buildings 116 
 
 — quantity of vapour absorbed by 1 76 
 
 — vents in pipes, necessity for 16, 156 
 
 — vents, proper size of 17 
 
 — vents, proper position of ... , 46, 156 
 
 — and water, relative weights of 17 
 
 Angles vertical, their effect on circulation 36 
 
 Arnott, Dr., his hot-air stove 1 93 
 
 Ascent of water in vacuo 130 
 
 Bars for furnaces, size of 79 
 
 Boilers, shape of 66 
 
 small, objections against them 68 
 
 • surface of, exposed to the fire 71 
 
 surface of, required for certain lengths of pipe .... 70 
 
 Boiling point, influenced by pressure 131 
 
 Branch pipes, their effect 22, 53 
 
 Brick flues, effects of I93 
 
 Capacity of Boilers, proper proportions for 66 
 
 Carbonic oxide, effect of breathing 1 95 
 
 Centrifugal force, effect of 148 
 
 Circulation of water 7 
 
 ■ erroneous theory of 8 
 
 cause of 10 
 
 through inclined pipes 13 
 
 effects of gravity on 15 
 
 velocity of 33 
 
 below the boiler 44 
 
 Cisterns, supply, size, and position of 48 
 
 Close-topped boilers, advantage of 18 
 
 Cocks, size of 55 
 
 Coal, quantity of, to heat different sized pipes 121 
 
 Compression of water 21 
 
214 INDEX. 
 
 PAGE 
 
 Conducting power of air - 83 
 
 Conduction and Radiation, erroneous theory of 83 
 
 of heat, effect of surface on 84 
 
 Condensation of vapour on windows 201 
 
 Connecting pipes, size of 55 
 
 Colour, effect of, on heat 96 
 
 Cooling, influenced by shape of surface 62 
 
 power of glass . . . . , 104,112 
 
 Cost of burning gas for fuel 198 
 
 Deposits in boilers, effect of 68 
 
 . removal of 164 
 
 Effects of heated metallic surfaces ] 44 
 
 of thickness of bodies on their cooling powers . . . .100 
 
 Elasticity of air, effect on the conduction of heat 84 
 
 Experiments on the cooling of iron pipes 1 02 
 
 Falling bodies, velocity of descent of 32 
 
 Fluids, motion of 17 
 
 Freezing of water in pipes, effects of 1 65 
 
 Friction of water in pipes, effect of , .... 34 
 
 relative amount of 52 
 
 Furnaces, construction of , 75 
 
 proper size of 79 
 
 Gas stoves, their effect , 196 
 
 hydrogen, its cost when used for fuel 198 
 
 Glass, cooling power of 104 
 
 surface of in buildnigs, how to calculate 115 
 
 Gravitation of falling bodies 31 
 
 Heat of water and steam compared 59 
 
 Heat, simple 83 
 
 loss of, by contact with air 86 
 
 radiation of, influenced by surface 86 
 
 radiant, law of 91 
 
 loss of, effect of thickness of metals on 94 
 
 effect of colours on the radiation of 96 
 
 quantity of, obtained from coals 109 
 
 Heated metallic surfaces, effect of on air 144 
 
 High pressure system of warming 133 
 
 Hot-air stoves, effect of on the human body 1 90 
 
 Hydrogen gas, effect of on the animal economy 189 
 
 Iron pipes, loss of heat in Ill 
 
 strength of 137 
 
 temperature of maximum strength 138 
 
 crystallized 139 
 
 Joints of pipes 160 
 
INDEX. 215 
 
 PAGE 
 
 Kewley's syphon apparatus 128 
 
 Latent heat of steam 58 
 
 Law of the smes 91 
 
 Lead paint, effect of on radiation 95 
 
 Main pipes, proper size of 53 
 
 Metallic surfaces, effect of on air, when heated 145 
 
 Moisture reduces the effect of heating apparatus 124 
 
 Motive power 24 
 
 how to increase the 28 
 
 Nobili and Melloni, their experiments on heat 83, 93 
 
 Nott's hot-air stoves 191 
 
 Obstructions to circulation of water 41 
 
 Oxygen, quantity of consumed in respiration 1 70 
 
 Permanence of temperature 60 
 
 Pipes, expansion of 49 
 
 size of for different purposes 64 
 
 iron, loss of heat in Ill 
 
 rule for calculating requisite quantity of . . . . 117,124 
 
 joints of 160 
 
 Pressure of water 11, 19 
 
 Rate of cooling influenced by shape of surface 62 
 
 Radiation of heat influenced by temperature 88 
 
 by surface 86 
 
 by thickness of body 94 
 
 • the inverse of conducting power 93 
 
 not affected by colour 98 
 
 Repulsion of water by hot iron 68 
 
 Rotary float circulator 148 
 
 Saline deposits from hard water 164 
 
 Salts, quantity of, in hard water 167 
 
 Specific heat 98 
 
 ■ of air and water 110 
 
 Steam, quantity of heat contained in 58 
 
 high-pressure, does not scald 142 
 
 Stop-cocks, size of 56 
 
 Supply cisterns, size and position of 48 
 
 Surface, effect of, on the conduction of heat 84 
 
 on the radiation of heat 86 
 
 Syphon, motion of water in 31 
 
 Table of motive power, and pressure of water 27 
 
 of friction in pipes 52 
 
 of surface of boiler, to heat a given quantity of pipe . . 70 
 
 of area of furnace bars 79 
 
 of ratio of cooling 85 
 
216 
 
 INDCX. 
 
 PAGE 
 
 Table of velocity of cooling by radiation 88 
 
 of radiating power 92 
 
 of conducting power of metals 93 
 
 of cooling of iron pipes 102 
 
 of glass 103 
 
 power of wind 106 
 
 i of pipe required to heat any building 119 
 
 of coal 121 
 
 of strength of iron decreased by heat 140 
 
 of discharge of air through ventilators 181 
 
 of pressure of steam 205 
 
 of vapour in air 206 
 
 of expansion of air 207 
 
 . of specific gravity and expansion of water 208 
 
 of specific heat and expansion of various bodies .... 209 
 
 . of effects of heat 210 
 
 of contents of pipes 211 
 
 of strength of materials 212 
 
 Time required to heat buildings 123 
 
 Vapour, quantity of, from the human body 170 
 
 condensed on windows 202 
 
 Velocity of circulation 32 
 
 Ventilation, amount of, for summer and winter 177 
 
 different modes of 184 
 
 Ventilators, discharge of air through 179 
 
 Vertical angles, their effect 35 
 
 height, effect of the increase of 30 
 
 Water, a bad conductor of heat 8 
 
 . cause of circulation of 10 
 
 pressure of 19 
 
 compression of 21, 141 
 
 . • expansion of 48, 134 
 
 quantity of heat contained in 58 
 
 repulsion of, by hot iron 68 
 
 . quality of, used in boilers 164 
 
 velocity of circulation of 33 
 
 Wind, cooling power of 104 
 
 not prevalent in the coldest weather 113 
 
 allowance for the effect of 113 
 
 THE END. 
 
 Gilbert & Rivington, Printers, St. John's Square, London. 
 
Green on Diseases of the Skin 
 
 SECOND EDITION. 
 4_ 
 
 Just published^ in 1 thick vol. %vo. 
 
 WITH TWO ILLUSTRATIVE COLOURED PLATES, PRICE lis. BOARDS, 
 
 A PRACTICAL COMPENDIUM 
 
 OF THE 
 
 DISEASES OF THE SKIN, 
 
 INCLUDING 
 
 A PARTICULAR CONSIDERATION OF THE MORE FREQUENT 
 AND INTRACTABLE FORMS OF THESE AFFECTIONS. 
 
 BY 
 
 JONATHAN GREEN, M.D. 
 
 40, Great Marlborough Street, 
 FORMERLY SURGEON IN HIS MAJESTy's NAVY, AND MEMBER OF THE 
 ROYAL COLLEGE OF SURGEONS, LONDON, &C. &C. 
 
 BY PERMISSION) 
 
 DEDICATED TO SIR HENRY HALFORD, BART. 
 
 Physician to thf. King, &€* &c. &c. 
 
 Whittaker & Co., Ave Maria Lane ; to be had of all Booksellers. 
 
 • — 
 
 It has been the author's aim in this Compendium to condense 
 within the smallest possible space; not only the results of his own 
 experience, but the whole amount of practical information extant 
 upon this highly important class of diseases. His most particular 
 attention is constantly given to the characters by which they may 
 be distinguished one from another, and to the most approved and 
 available means of treatment recommended for the cure. 
 
REMARKS OF THE MEDICAL AND GENERAL PRESS, 
 
 ON Tllli riRST EDITION. 
 '* It is almost supcrHuous to say, that every professional reader ^yllo wishes to 
 be successful in the management of cutaneous diseases, will find it his interest 
 to study thoroughly the method of treatment recommended by Dr. Green."— 
 Edinburgh Medical and Surgical Journal. 
 
 The Practical Compendium of Dr. Green forms a popular and very usehil 
 introductory work to the larger one of Ilayer. His observations on Impetjgo 
 and Porrigo are certainly the most judicious we have ever read ; they are 
 derived from sound pathological views. To the student of medicine we do not 
 hesitate to recommend the Compendium of Dr. Green in preference to Bate- 
 man's Synopsis, (no mean praise) as more simple in its descriptions, and more 
 practically useful" in its therapeutic instructions. It is unnecessary to say more 
 of this work." — Medico-C/iirurgical Review. _ r m i 
 
 Upon the whole we are much pleased with this book; it cannot fail to be 
 instructive, as it is replete with the results of long and successful practice."— 
 Medical Quarterly/ Review. , , . i 
 
 " We earnestly recommend those who are interested in the subject, not only 
 to read this book, but to put the efficacy of the agents to the test."— London 
 Medical Gazette. . 
 
 " So far as the production of a compendium of all that is known on the 
 pathology, etiology, diagnosis, and treatment of cutaneous diseases is concerned, 
 the author seems to have succeeded in his object." — Lancet. 
 
 *' It is an excellent compendium, evincing great experience and success on 
 the part of the author." — London Medical and Surgical Journal. 
 
 " We can state from our own knowledge of the benefits experienced by 
 numerous patients, and heartily recommend both the work and the system it 
 advocates." — Literary Gazette. 
 
 " Dr. Green's book will recommend itself. It is not a mere book of nomen- 
 clature system, but enters largely into therapeutic details, which are mostly 
 satisfactory, laying down very precise rules for the management of herculean 
 remedies in the treatment of maladies that have long been the opprobria medi- 
 corum." — AthenfEum. 
 
 We take leave of this work with the full conviction that the author^ has 
 rendered an important service to the public, furnished the practitioner with a 
 most valuable book of reference, and evinced in his elucidation of an obscure 
 class of diseases, a thorough knowledge of their causes, treatment, and method 
 of cure." — Metropolitan. 
 
 " Such a work as the present has long been wanted. More empirical reme- 
 dies are in use, and more mistakes made in the treatment of cutaneous diseases, 
 than in any other class of disorders. The clearness with which Dr. Green has 
 classed the diseases of the skin, and the remedial details into which he has so 
 largely entered for the management of those intractable diseases in all their 
 varieties, render the present volume a most valuable addition to medical litera- 
 ture. It ought to obtain a place in the library of every professional adviser." — 
 Court Journal. 
 
 BV THE SAME AUTIIOU, 
 
 Published by Churchill^ Medical Bookseller, 
 prince's street, so ho, 
 
 OBSERVATIONS on the UTILITY of FUMIGATING and 
 other BATHS, with Abstracts from the Official Documents, ordering this Mode 
 of Treating Diseases to be adopted in the French Hospitals, and which rapidly 
 extended throughout the Continent; together with Ninety-two important Au- 
 thenticated Cases. Price Is. 6d. also, 
 
 A CHART of the DISEASES of the SKIN, wherein is defined 
 the distinguishing Characters by which they may be known, and the effects of the 
 Fumigating Baths in the Treatment are shown in the last column. Price Is. Qd, 
 
A 
 
 SHORT ACCOUNT 
 
 OF 
 
 FUMIGATING, HOT AIR, 
 
 AND 
 
 This account lays claim to confidence, as it is supported by the first 
 Medical Authorities, in this Country and on the Continent. 
 
 The above represents the Patent Fumigating, Warm Air, and 
 Vapour Apparatus for Baths, as introduced into England, early in 
 1822, by JONATHAN GREEN, M.D. They are improved upon 
 the plan of those used on the Continent, and of those directed to be 
 used in the Hospitals throughout France. 
 
 The left view shows the Bath open, and the right a person taking 
 the Bath, 
 
 LONDON : 
 40, GREAT MARLBOROUGH STREET. 
 1837. 
 
Fumigating, Hot Air, 
 
 In the treatment of various diseases Baths are very essential, and 
 have been much overlooked in this country. In a curative point of 
 view, immeasurably above all others are those administered in what 
 is called the Fumigating Apparatus, by means of which Medicines of 
 any degree of strength, and in the most favourable form for influ- 
 encing the system, viz. the Gaseous, are administered without unplea- 
 santness, or inconvenience to the patient. 
 
 No water is used in these Baths, except for Vapour. The Medi- 
 cines employed are such as the case may require, as Sulphur, Cam- 
 phor, Ammonia, Mercury, &c. &c., which, being converted by Heat 
 into the Gaseous form, surround the patient's body, the face only 
 being excluded; and as the Heat occasions absorption of the Medi- 
 cine, these Baths are particularly viseful in those cases, where the coats 
 of the stomach and bowels are too weak to receive the requisite remedies 
 in the ordinary way. 
 
 The temporary application of Heat, after this method, occasions 
 for the time an increased vigour to be given to all the internal and 
 external functions of the body, simultaneously, by which any hidden 
 or latent complaint is propelled outwards and through the pores of 
 the skin, as the Bath acts much on the principle of the cupping glass, 
 that is, drawing from within outwards. 
 
 The efficacy of this mode may be inferred from a knowledge of the 
 fact, that the milder forms of disease give way to the use of these 
 Baths alone. They may be taken by the most delicate persons and 
 children, being always tonic in effect, when properly administered, 
 and persons from their use are less liable to take cold.* 
 
 They are preservatives of Health, as they produce the good effects 
 of exercise, viz., increased and equal circulation and perspiration, 
 without fatigue. 
 
 The good effects of these Baths may be further judged of, as it is 
 indisputably admitted, that they — • 
 
 I. Equalize the circulation of the blood, and powerfully tend to prevent its 
 determination to the head, and likewise to remove giddiness, and prevent cold- 
 ness of the hands and feet. — See Dr. Green's Observations on Fumigating and 
 other Baths, Introduction. 
 
 II. They re-establish insensible perspiration, promote sweat, consequently 
 relieve or remove symptoms of inflammation ; therefore are indicated for gouty 
 and rlieumatic pains, swellings of the joints, lumbago, sciatica,, &c. — See London 
 Medical Repository/, Oct. 1823. 
 
 * See Transactions of the Royal Society, Vol. LXV. p. Ill, 484, and 494. 
 
and Vapour Baths. 
 
 III. They diminish nervous irritability, and have cured cases of tic doloureux. 
 — See Observations, p. 32. 
 
 IV. Most diseases of the skin, from rashes and pimples to leprosy, are best 
 treated by this method ; in proof of which the milder forms of skin disease give 
 way to this treatment alone. — See Medical and Physical Journal, December, 
 lH23-^and Oct. 1827-^and London Medical Repository, Apr. 1824. 
 
 V. They remove from the system the ill effects arising from the too free use 
 of mercury. -->S'e'e Cases in Observations, ^-c. p. 54-— 58, 
 
 VJ, They strengthen the stomach and give tone to the digestive organs, by 
 increasing the secretions. — See London Medical Repository, October, 1 824= 
 
 VII. They do good in all glandular and other swellings and obstructions, by 
 equalizing the circulation and quickening the activity of the absorbent vessels. 
 — See London Medical Repository, April, 1823. 
 
 VIII. They tend greatly to relieve all dropsical swellings submitted to their 
 operation. A common cold is always cured by these Baths, — See Observations, 
 S)C.p.37-S9, 
 
 IX. Dr. Green has yet had no case of ague which has not been cured 
 principally by them. And all slight affections of the above diseases, he believes 
 to be under the same control. — Sec London Medical and Physical Journal, 
 March, 1827. 
 
 After this statement, and in corroboration of it, it may be well to 
 bring before the reader's notice, though very briefly, the origin and 
 progress of these remedial means on the Continent, 
 
 To France the honour is due for discovering this mode of curing 
 various obstinate diseases, more successfully and speedily than by the 
 customary methods. The early trials by these means occasioned as 
 it were at the time a new era in the practice of Medicine. The minds 
 of all persons in Paris were greatly biassed in its favour, and it was 
 thought that all former modes of combatting diseases must succumb 
 to it. The French government (ever mindful of the public Health), 
 to set the matter at rest, and unequivocally to establish the merits or 
 supposed merits of the remedy, or otherwise, if found wanting, to 
 decry it, ordered separate Committees, composed of the leading Me- 
 dical Practitioners in Paris, to assemble at the Hospitals, and inves- 
 tigate the matter by trials, comparing these means with those already 
 in use ; and to insure impartiality, each of these Committees was pre- 
 sided over by an official officer appointed for the purpose, and the 
 results of the trials of each separate Committee was kept secret until 
 transmitted to a Central Committee. The conclusion only of the last 
 Report to the Government by the Central Committee is all that can be 
 adduced here ; it is as follows , — 
 
Fumigating, Hot Air, 
 
 CONCLUSION OF THE 
 REPORT OF THE CENTRAL COMMITTEE. 
 
 " We have given it our most deliberate attention, and urge that it should be 
 ur.ed in hospitals and great establishments. 
 
 " 'I'he Committee think it their duty not to dissimulate on the advantages of 
 this method, which cannot but be applicable also to the service of the Camp and 
 the Army. Done at a meeting held this twenty-second day of August, 1815. 
 
 Signed " LEROUX, 
 DUBOIS, 
 DUPUYTREN, 
 
 RICHERAND, . ^ , ^ . ^ . 
 HALLE 1 1* acuity ot Physic, Pans. 
 
 PINEL,' 
 PERCY, 
 
 Barons and Professors of the 
 
 After this the Fumigating Apparatus was ordered to be establislied in all 
 hospitals, prisons, poorhouses, &c. — See Memoirs and Beports on the Efficacy 
 of Fwnigations, printed hij order of the French Government, for General 
 Instruction — Translated by Dr. Price — Published by Longman (Sr Co. 
 
 The advantages of this new mode of treatment rapidly extended throughout 
 the Continent. — See the Woi k of Dr. De Carro ( the Sir Henry Halford of 
 Vienna) — Translated by Wallace — Published by Burgess Hill. 
 
 In 1 822, at St. Louis, the largest hospital in Paris, the surprising number of 
 127,752 of these Baths were administered ; as each year, from their first intro- 
 duction, had contributed to increase the estimation in which they were held. — « 
 See Dr. Bayer's Work, Vol. I. p. xxvi. — Published by Churchill. 
 
 In 1833, a work by Drs. Cazenave and Schedel, physicians to the hospital, 
 shows that the number had increased to upwards of 150,000 at the said hospital 
 in one year. — See Vol. I. p. xxxi. — Published by Balliere, Regent Street. 
 
 In November, 1836, the writer was at the Hospital of Saint Louis, 
 and found that in the years 1834 and 1835 upwards of the astounding 
 number of 180,000 had been administered each year, and for the year 
 1836, the number, it was judged, would be about the same, the Baths 
 being always in occupation. 
 
 If it is borne in mind that these Baths are erected at the other 
 hospitals, prisons, poorhouses, and other large establishments, it will 
 
and Vapour Baths. 
 
 at once appear evident how much importance is attached to theri as 
 curative means on the Continent, Here, it is true, they are not he] d in 
 so much estimation ; but this is owing to their not being much known. 
 This is not a bathing nation, and all new systems have many opposing 
 influences to contend with — these things are managed better in France. 
 The writer has the satisfaction of adding, that he has been required to 
 superintend their erection at three of our Metropolitan Hospitals, 
 and no doubt in time the remedy will attain its due share of popu- 
 larity in this country. At present, it is mostly known to be abused, 
 by misapplication and bad management, whereby this means of relief 
 runs much risk of being brought undeservedly into disrepute ; it is, 
 therefore, with pleasure, the writer can submit the following testimo- 
 nies from the Medical Press. 
 
 " The Fumigating Bath, as a Therapeutic xA-gent, is too important to be 
 trusted in any other hands than Medical, and from personal observations, we 
 can testify, that Ur. GREEN'S Establishment is by far the most complete in 
 London, and as it is carefully supenntended by himself, it deserves the Patron- 
 age of the Profession, and the confidence of the Public." — Medical and Chirur- 
 gical Review. 
 
 " In the adoption and effective application of one description of Therapeutic 
 Agents, Dr. GREEN, though not original, has very great merit. We allude to 
 the employment of those agents, which act directly on the cutaneous surface, in 
 the shape of Fumigating Baths. No doubt can be entertained of the efficacy of 
 these methods; and it is quite clear that many diseases, which are quite intrac- 
 table under the ordinary remedies, particularly of the Skin, speedily yield to 
 agents applied in this manner." — Edinburgh Quarterli/ Medical and Surgical 
 Journal. 
 
 THE BATES ARE THREE FOR A GUINEA. 
 
 Dr. GREEN cannot interfere in the cases of any Patients coming 
 from Medical Gentlemen, and is at home for consultation daily from 
 \2 till 5 o'clock, (Sundays excepted). 
 
For Domestic Use, as a most Efficient VAPOUR BATH, for Local or General 
 Purposes, the Writer can recommend the Jekyll Bath. 
 
 The above shows Captain JehyWs Paienl Povlahle Vapour Balk, price Twelve Guineas, with 
 Seat, Curtain, and Dresses, complete, accompanied with a book of cases and ample directions. 
 
 The Fumigating Baths are necessavily Fixtures. But tlie above represents a Por- 
 TABLE Vapour Bath, of very superior construction and manufacture, suitable to 
 Invalids who cannot leave their room, or for persons travelling, as a Vapour Bath 
 can be thus had in any place where there is a fire, and in as short a space of time as a tea- 
 kettle can be made to boil, and during which time the bath is put m readiness. It can 
 be used in a drawing-ioom without soiling the cleanest carpet. As a Vapour Bath, 
 it leaves nothing more to be desired, and is so durable as to be handed down from 
 family to family, and, including the seat for taking the bath, it occupies but a foot and 
 a half square. The whole is packed in a mahogany box, which slides and packs 
 between the legs of the seat. It can be used locally or generally, and with the head 
 inclosed or not, at the discretion of the bather. They were invented by the proprietor 
 (an amateur engineer of acknowledged excellence), and never made with a view to 
 profit ; and since the decease of Dr. Kentish are onlv to be had by order, to and from 
 Dr. GREEN, No. 40, GREAT MARLBOROUGH STREET. 
 
 description of the plate. 
 
 A. The Bath, as being taken. 
 
 B. The Boiler, with the safety-valve and 
 
 connecting tubes, 
 
 C. The Apparatus shown in perspective. 
 
 1. The Elbow- Joint, which attaches to the 
 
 Boiler. 
 
 2, Connecting Tubes. 
 
 3. Folding Tube with Key, to control the 
 
 Vapour. 
 
 4. The Disperser, into which perfumes may 
 
 be put. 
 
 5. The foot- stool. 
 
 6. Caned seat. 
 
 7. Telescope upright, with Spring Hoop, to 
 
 suspend the Curtain. 
 
GETTY RESEARCH INSTITUTE 
 
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