LIBRARY OF THI: UNIVERSITY OF CALIFORNIA. Received... -NOV 19-1&9J- , 18 A ccessions No. ^5/ J74r^ Shelf No. . THE THEORIES AND PRACTICE OF CENTRIFUGAL VENTILATING i: ;;'':- MACHINES. ,' : V BY DANIEL MURGUE, ENGINEER -TO THE COLLIERY COMPANY OF BESSEQES. TRANSLATED, AND SUPPLIED WITH AN INTRODUCTION, BY A. L. STEAYENSON, LONDON: E. & F. N. SPON, 16, CHARING CROSS. NEW YORK : 35, MUKEAY STEEET. 1883. \ INTRODUCTION. LITTLE if anything was done towards the application of machinery to the purposes of ventilation until very recent years, although, so early as the year 1657, Agricola, in his interesting work " De re Metallica," gives particulars and a drawing of a mechanical ventilator for mines, driven by water-power, and at the Hartz mines, nearly 200 years ago, another, somewhat similar to the Struve, was in operation. In the year 1849, Mr. Warrington Smyth referred to this in his evidence before the House of Lords' Committee, and at the same time Mr. Struve said his ventilator at the Eaglesbush Colliery, then the only place where it was yet applied, began its work in February 1849. Mr. Brunton also then x explained and gave drawings of his centrifugal ventilator. But so late as the year 1852 a Committee of the House of Commons reported : " Your Committee are of opinion " That any system of ventilation depending on complicate machinery is undesirable, since under any disarrangement or fracture of its parts the ventilation is stopped or becomes inefficient. " That the two systems which alone can be considered as rival powers are the furnace and steam jet. u Your Committee are unanimously of opinion "that the steam jet is the most powerful and at the same time least expensive method for the ventilation of mines." a 2 iv INTRODUCTION. In 1861 the centrifugal fan at Elsecar was described to the North of England Institute of Mining Engineers by the late Mr. J. J. Atkinson, and to him must be given the credit of having, in several valuable papers on the subject, first shown clearly the superiority of mechanical ventilators over every other system. From that time until now the question as to which fan is the best has been a source of constant contention ; every fresh invention being introduced as at least 10 per cent, better than anything which preceded it. Numberless experiments have been made by private individuals and committees to ascertain the truth of these questions. Nearly all the results obtained have varied, and the question to-day still remains unanswered " Which ven- tilator is the best ; and which, taking all circumstances into account, should I, as a mining engineer, adopt ? " The cause of this unsolved state of the problem is not far to seek. The useful effect of a fan is not the only question involved. We must consider 1. First cost ; 2. Durability; 3. Efficiency. The enormous first cost and want of durability of some of our largest ventilators, has overshadowed in a great degree the question of efficiency, especially where, as at many collieries, steam is obtained from the heat of coke-ovens. Some of the results published as to efficiency, are the work of experi- menters quite unused to the rigorous accuracy demanded in scientific research, still it is very important, and to appreciate reliable data, such for instance as the recent report of the North of England Institute, there is wanted a general know- ledge of the laws governing the variation in results under varying conditions of work. To supply this hitherto un- INTRODUCTION. V supplied need of the engineer in England, I have been led to translate and publish the very excellent treatise of M. Murgue. Many attempts have been made to follow these laws of ventilators, but nothing approaching the lucidity of his methods has been attained ; a little attention and study on the part of those who care thoroughly to understand the various questions involved, will give a perfect mastery over them, and then when seeking to know which is the best ventilator, they will at least be able to make the selection with their eyes open. The leading ideas given by M. Murgue are First, That every mine may be assimilated to an orifice in a thin plate, which he calls its " Equivalent Orifice." Second, That a ventilator, even whilst exhausting the air from the mine, forms at the same time an obstacle to the passage of this air, causing a sensible loss of duty, so that the depression produced by the ventilator is always higher than what we observe in the galleries of approach, some part of this depression being employed in overcoming the various resistances in the fan ; this he treats as the " Orifice of Passage" Third, The theoretical depression or water gauge, due to the speed of the periphery, is in a perfect fan equal to twice the height of column necessary to generate such velocity in a falling body. This meets a difficulty experienced by a writer on the subject,* who says " It is especially worthy of notice that the water gauge indicated at the inlet is greater than the theoretical result," the hitherto recognised theory having u 1 been , where u = speed in feet per second, and g = 32 2. ^9 Fourth, That there is an initial depression which each fan * See 'Proceedings of Northern Mining Institute,' vol. xiv., p. 80. vi INTRODUCTION. gives when acting on a closed space, and which approaches the theoretical limit in proportion to the perfection of the ventilator. Fifth, That this depression gradually varies and lowers according to conditions. A little further explanation of these theories seems de- sirable for the benefit of those whose time has been more given to the distribution of air in mines, than to its economic production. The equivalent orifice depends upon well known laws of the flow of fluids : 1st. That the speed of flow is the velocity due to the height of fall or height of column of the flowing air, which is represented by the formula for gravity = r V = 2nd. That the quantity which passes through an orifice in a thin plate is two-thirds or 65 that of the quantity due to the area of the full orifice, and the formula then becomes, for what is known as the " vena contracta," Q = 8m a A/h, where Q = quantity, m = 65, a = area, and h the height which must be reduced to air column, or as M. Murgue puts it reducing this we get v a (or equivalent orifice) = INTRODUCTION. where 8 = 1000, and 8 = 1*2000, or the relative densities of water and air. Simplifying this for water gauge as usually taken' in inches V -70V a = =-, or " 't and if we assume these as normal densities we may remove the fraction and obtain V 0-0243 V a - -- - or 41-26 Vh Vli In this case V = volume in cubic feet per second ; but as we generally speak of cubic feet per minute we may say 0-403 V _ taking V = 1000 cubic feet per minute, and h = inches of water gauge. The great value of this fiction is that it enables us to grasp at once the conditions under which a fan is working. We hear of one machine giving 100,000 cubic feet per minute under a water gauge of 3 inches, and of another where 75,000 cubic feet is got with a water gauge of 4 inches ; but this is not a tangible statement. If, however, we are told that the equivalent orifice of the first mine is equal to 22 feet, whilst that of the second is only 14, the difference is clearly demonstrated. Then as to the Orifice of Passage, as M. Murgue says, the fan suited to blow a cupola may give a depression as great as the largest Guibal, but it would be useless to ventilate a mine its orifice of passage is insufficient. To obtain this in any case we must refer to his theory of initial and effective depressions (p. 4) h = H - h M Vlii INTRODUCTION. where h represents the deficiency or difference between the initial and effective water gauge ; and we see a little further h a 2 on that ^ = -T, or as the orifice of passage diminishes h o the loss of effective depression increases. To calculate the area of this orifice of passage we must refer to its value in the equation H - h = h = M V 2 , V 2 or, Ji = That is to say, after finding for any ventilation the value of the initial and effective depression, the loss or useless depres- sion is equal to a function of the volume which depends upon the orifice of passage, and from the above equation ~v m V 2 62 2 h 2 g reducing of course h to the density of air in feet. We are now enabled to understand what is termed " the characteristic curve of the ventilator." In order to compare two machines they are regulated to the same speed of periphery, or their results may be easily reduced to equal speeds since the volume varies as the revolutions and the depressions as the squares of the speeds. The mine is altered, to say five different conditions : first by obstructing the passages ; then in the normal state ; and afterwards by opening some of the doors. With the equivalent orifices of these five different mines, or conditions of mine, plotted as abscissae, and the volumes as ordinates, we get a curve which shows clearly the effective- ness of each fan, and is called its " characteristic curve" We are next shown how the effective depression varies and INTRODUCTION. ix diminishes by a function of the volume depending upon the orifice of passage. The experiments upon the four different ventilators tested by the Commission of Gard are tabulated, and from them an equation for each is obtained, giving the initial depression and its coefficient of diminution as the volume increases. Taking, say Nos. 1 and 2 experiments on the Creal fan, with the square of the volume and depression observed, we get x -y (89,283) = 1-0598, x - y (195,766) = 1-0183, and from these constants are found. The average of the various experiments should be taken. Little more need be added, but a short reference to the remarks on the effect of the natural ventilation of the mine upon such investigations, given in the report of the Com- mission of Gard, of which M. Murgue was a leading member, will be useful.* The effect of natural ventilation is much less than is com- monly supposed, since it is not the yields which are to be added, but the depressions, and the volume to be obtained therefore, is like the hypothenuse of the rectangular triangle, thus say in cubic metres x = \/20 2 4- 5 2 = 20 615, and as all conditions additive or subtractive are covered by the equivalent orifice, it may be entirely neglected. If then, as is clearly demonstrated, the covered Guibal with evasee chimney most nearly meets theoretical requirements, how can its acknowledged defects in point of size, structural weakness, and heavy cost, be best met, so as to produce a machine perfect in every respect ? The answer is to be found in a ventilator I have recently designed, and which will be at work at Pagebank Colliery by the time this issues from * See ' Bulletin de la Societe de 1'Industrie Minerale,' 1878, p. 495. 6 X INTRODUCTION. the press. It is 20 feet diameter, built with, and from, a central wrought-iron diaphragm, like the Kammel and Schiele fans. It has the vanes in shape according to M. Murgue's demonstrations, made of iron and riveted to the diaphragm with angle irons, the sheet-iron cover, evasee chimney, and sliding shutter of Guibal type, with air admitted on both sides. The fan is driven by ropes, and will run about 110 revolutions, and much more if needed. A. L. STEAVENSON. DURHAM, 3rd February, 1883. THE THEOEIES AND PKACTICE OP CENTRIFUGAL VENTILATING MACHINES. IN publishing towards the end of 1872 the first part of this study, I entertained the hope that I should be able shortly to announce a new theory, firmly based on experience with large ventilating machines by centrifugal force a theory which up to that time appeared to me to be still somewhat cloudy. Seven years have since elapsed, and to-day only am I able to keep the promise I then made. This long interval will surprise few people who know how difficult it is to con- duct experimental researches and make them subservient to the exigencies of active life. It has not been altogether sterile, for beyond the unconscious labour of thought which I have given, by the sole aid of time the matter has become much clearer, and it has been permitted to me to add my study on the works incidental to the Commission on Ventila- tion of the district of Gard the results of which have been published in the later volume of 1878 being myself a member of that Commission, with M. Aguillon, then Govern- ment Engineer for Alais. The theoretical study which I propose to develop here comprehends not only that on ventilators with centrifugal force, but also many machines now almost abandoned which draw in the air by oblique surfaces, such, for example, as the ventilator or screw by B \ THE THEORIES AND PRACTICE OF M. Motte, and the helix, by M. Pasquet, and that with vanes like a windmill by M. Lesoinne. M. Devillez distinguishes them as ventilators by direct impulsion. But to separate these from the centrifugal machine does not seem to me to be justified, these machines being in fact exactly the same as those with centrifugal force, producing in the atmosphere of the mine a certain depression, which is ruled by the square of the speed. If the seam is thin, the circulation obtained is small ; if it is thick the result is considerable, but the depres- sion remains in every case theoretically the same. It is not, however, the same with the pneumatic machines of Fabry and Lemielle studied in the first part of this work, their mode of action being absolutely the reverse. These machines draw the air from the interior, cutting it off and throwing it out, so to speak, in equal quantities. It is not then the depression which remains constant, but the volume drawn. This difference of action between the two classes of machines presents itself with sufficient clearness. We shall show shortly how to replace the word " volume " by the word " depression," and conversely, so as to pass from the one to the other without any change in the theory. Also, having in my preceding memoirs on pneumatic machines, with the approbation of my friends, used the generic denomination of Yolumogen ventilators, I am now naturally led to call the machines which I discuss to-day Deprimogen ventilators, and I will shortly enumerate their principal characteristics and advantages. First, their mechanism is extremely simple ; all is reduced to the rotative system, turning on two bearings if the axis is horizontal, and on a foot-step and collar if it is vertical. Second, they leave free communication between the interior and the exterior air. Third, they can only give in thin seams a feeble result, but for thick seams otherwise. All their characteristics are in complete opposition to those of the well- known volumogen ventilators. I shall apply at every step CENTRIFUGAL VENTILATING MACHINES. 3 in the course of the discussion which I am undertaking the method of the equivalent orifice through a thin plate a method which I have developed in my two previous studies. I shall employ as notations the letter a to designate the equivalent orifice, V will be the volume of air yielded per second, h will express the depression, for convenience of cal- culation, in the column of the fluid in movement, that is to say, in the column of air. I am supposing that air is an incompressible fluid, which is perfectly legitimate under the conditions, and on all occasions I shall simplify as far as possible every remark, knowing well that for a theory to be useful, the supreme quality after exactness is simplicity. 1. ESTABLISHMENT OF Two GENERAL FORMULA FOR DEPRIMOGEN VENTILATORS. Let us consider the deprimogen ventilator placed on a mine and turning at a rigorously uniform speed. Profiting by the fiction of the equivalent orifice, let us replace the mine ventilator by an orifice in a thin plate, which we can reduce or increase at will. If we suppose at first the equi- valent orifice equal to zero, that is to say, that the mine is completely shut off, the ventilator will produce in a confined space adjoining the ouie or inlet a certain depression, which I will call H. If now I open out and increase by degrees the equivalent orifice, what will become of this depression ? Theoretically it should remain invariable, the exhausting power of the vanes acting equally well upon the air whether in motion or in repose. But in effect it will be weakened in proportion as the ventilator is traversed by larger volumes, and finally it will disappear when the equivalent orifice B 2 4 THE THEORIES AND PRACTICE OF is increased to infinity. If I call this gradual reduction of initial depression h , the effective depression may then be expressed by the equation Ji = H - h . (1) h may increase from zero to H. What are the causes of this fall in depression h ? Evidently the frictions and losses of active force which the air experi- ences in passing through the ventilator frictions and losses which increase in proportion to the volume of air yielded, and absorb an increasing fraction of the initial depression. Those who have occupied themselves in studying this theory have generally sought to determine by calculation these frictions and losses of active force, which always leads them to complicated expressions. It has appeared to me much more simple to introduce here the method of the equivalent orifice, which evidently lends itself sufficiently well to represent the difficulty of the passage of the air through a ventilator as well as through a mine. I have already spoken in the second part of this work of this new application of the method, and I call it the orifice of passage. FIG. 1. L | 4- a/ t I We may, then, replace in imagination the mine and its ventilator by two orifices, a and o, placed one behind the CENTKIFUGAL VENTILATING MACHINES. 5 other (Fig. 1), and successively traversed by the current of air ; the first in virtue of the depression h, the second in virtue of the depression h volume, depressions, and orifices being connected by the formula for flow through a thin medium : V = 0-65a\/~2~pr (2) V = 0-650 ~2~0X (3) From these two relations I obtain the interesting proportion Ji a 2 r 1 h c? If now we substitute for h , in the equation (1)," the value which results from this proportion, it will become ,;' l =, H -* and, resolving it by the proportion to h, Such is the formula for the effective depression h. To obtain that of the effective volume V, it suffices to introduce the preceding value of h in equation (2). It becomes then, all reductions made, v , 0-65W2JH (5) From this we learn at once to determine the initial depres- sion H as a function of the diameter and of the speed. The equivalent orifice of the mine a is supposed to be known ; that of the passage o depends upon the dimensions and arrange- ments of the ventilator, and we see that it may be determined a priori. The depression and the volume of air yielded are found then to be expressed by our two formulae (4) and (5), THE THEOKIES AND PRACTICE OF with the aid of known quantities, which was the object to be gained. This forms but the first part of our theory, and there re- mains for us to see how to determine the initial depression H. This determination will be the object of the next paragraph ; but before undertaking it, I have pleasure in showing the wonderful parallelism which exists between the preceding theory and that which I have proposed in the two former parts of this study for the volumogen ventilator. I have said already that to pass from the one to the other it is sufficient to change the word " volume " to that of " depression," and conversely. This will be clearly seen from the following. Volumogen. In theory the volumogen ventilator should give a constant volume of air, equal to that which it affords when working freely on the atmosphere. In reality the volume obtained is always less than the theoretic volume, because of the unavoidable play of the joints of the machine, which gives place to a re- entry direct from the exte- rior air. If W represents the theo- retical volume, Y the re- entry of air, and V the effec- tive volume, I may write the equation V = W- V ; a being the equivalent orifice of the mine, we will call o the equivalent of the pas- Depr Imogen. In theory the deprimogen ventilator should afford a constant depression equal to that which it reaches when acting upon a closed space. In reality the de- pression obtained is always less than this initial depres- sion. A great part of this latter will be found to be absorbed by the frictions and losses of active power in the air traversing the machine. If H represents the initial depression, h the part ab- sorbed by the frictions, h the effective depression, I may write the equation h = H - Ji ; a being the equivalent orifice of the mine, we will call o the equivalent of the passage, CENTKIFUGAL VENTILATING MACHINES. sage, more or less compli- cated by the re-entry of the air. The depression produced by the ventilator being the same over the two orifices, the corresponding volumes will be evidently in the same proportion as the orifices themselves ~V o V = ~a If, then, I substitute for V in the first equation the value resulting from the preceding proportion, I ob- tain the equation V= W - V-; a which, reduced in the pro- portion to V, will give the first formula required vvJL If, now, in the value of the given depression by the well-known formula for the flow of air through a thin medium, /- Y V/i = o^7 If I replace V by the preced- ing value, I obtain the second formula W 0-65 (a + o) more or less complicated, formed in the ventilator it- self. The two orifices a and o being traversed by the same volume of air, we easily perceive that the correspond" ing depressions are in the inverse proportion of their squares If, then, I substitute for h in the first equation the value resulting from the pre- ceding proportion, I obtain the equation which, reduced in the pro- portion to h, will give the first formula required ll -"""- _ If, now, in the value of the given volume by the well-known formula for the flow of air through a thin medium, V = 0-65a If I replace h by the preced- ing value, I obtain the second formula V _ ' 65a o* 8 THE THEORIES AND PRACTICE OF We see the parallelism is perfect, and also that their characteristics are absolutely opposite. Thanks to this re- markable reciprocity, the two theories render each other more clear ; and I may say that more than once the volu- mogen ventilator has assisted me to understand the depri- mogen. In reality, it is not between the volume and the depression that the reciprocity is established, but between the volume and the square root of the depression. But that changes nothing in the curious result which I am about to show. Of the two formula which we are about to establish, as well for the volumogen ventilator as for the deprimogen, the most important is evidently that which gives the volume of air yielded per second. This volume is most especially interesting. The curve expressed by this formula, the equivalent orifice being drawn as abscissae and the volume of air as ordinates, characterises most distinctly the venti- lator to which it is applied, and furnishes a very simple and sure means to compare different machines. It is this curve which the Commission of Gard has set itself to deter- mine for the six ventilators submitted to their tests. They have given it the name of the characteristic curve of the ventilators. 2. DETERMINATION OF THE INITIAL DEPRESSION FOR VENTILATORS WITH CENTRIFUGAL FORCE. I preserve the name of Initial Depression for that value of the depression which is shown when the mine is shut off and rests virtually constant when we do away with the friction of the air. We know that in the volumogen ventilator the mechanical combinations which give place to the volume CENTEIFUGAL VENTILATING MACHINES. 9 engendered, differ absolutely in one machine from those in another, and require each time, for the determination of the volume, special methods of calculation. It is the same for deprimogen ventilators ; each type of machine produces the depression by particular methods, each requiring their special calculation. But I will not occupy myself here except with the centrifugal ventilator, the most perfect and therefore the most interesting of all. I will study first the uncovered ventilators with centrifugal force, such as were made by the first inventors (Combes, Letoret, Lambert, &c.), to whom the cover appeared, no doubt, the greatest obstacle to the free escape of the air into the atmosphere. This manner of looking at it, very plausible at first sight, is in reality quite erroneous. We know that to M. Guibal belongs the honour of having first shown that the cover is indispensable for making the ventilators develop their full useful effect. To-day almost every ventilator at work on the collieries possesses this ingenious addition. In order to proceed with regularity we must begin with those which have not got them. To avoid any difficulty in the establishment of my calcu- lations, I will suppose that the air of the mine before reaching the ouie is expanded in a large chamber where its speed may be considered almost nothing. In reality, this vestibule will be more useless than useful, but for our theory it has the ad- vantage of placing the ventilator between two motionless atmospheres, the air being drawn from one and thrown into the other. The situation is clear, and the analysis equally so. I propose, then, in the course of this discussion, to consider only an ideal ventilator, presenting no play, nor shocks, nor losses of quantity of any kind. In practice, of course, it is very far from attaining this ideal, the necessity of a simple construction, so as to work with certainty, obliging us to preserve numerous imperfections in detail ; but to introduce these imperfections in the calculation would be to 10 THE THEORIES AND PRACTICE OF expose ourselves to inextricable complications. It is much better to go straight to the theoretical result. The ventilator with centrifugal force without cover is re- presented in its essential features by Fig. 2, the vanes as drawn showing the profile somewhat bent and approaching the ouie in a manner to afford the desired inclination, so that the air penetrates without shock between these spaces. FIG. 2. These vanes are sufficiently numerous to assure the regular drawing of the air from the centre to the periphery without eddies or disturbances. I will call r the radius of the ouie or inlet, E that of the external circumference, CD the angular speed of rotation. The result, co E, expresses the absolute speed of the extremities of the vanes. This speed plays a preponderating role in all this discussion. I will call it the tangential speed, and I will mark it by the letter u. The depression produced by such a machine will result from a series of actions, some additive and some subtractive. We may, then, determine them successively and in their order, so as to draw the balance. First, the motionless air in the vestibule is brought CENTRIFUGAL VENTILATING MACHINES. 11 to the speed V , with which it traverses the ouie and penetrates between the spaces of the wings. There is then to the debit of the depression the height generative of this speed Second, the air once drawn between these vanes has a double movement, the movement relative to the dragging after the surface of the vanes, and the movement of drawing produced by the rotation of the machine, but theory requires that the total depression should be the sum of the elementary depressions due to each of these movements. Let us look first at the relative movement. The interval between two consecutive vanes forms an evasee canal which the air enters with a certain speed Vi, and leaves with a less speed V 2 . From this slowing action results, according to Bernouilli's theory, a gain of depression expressed by the difference YL_YI 20 20* But the speed of entry Vi is the resultant of two redt- angular speeds, the one V following the radius, the other &> r equal and opposite to the tangential speed of the wings. In the ideal ventilator which I have here supposed, the interior surface of the wings is directed exactly in accordance with this result, so that the composition of the speeds is produced without] obstacle, and the air slides without shock on the cutting surface of the vanes ; I may, then, replace in the preceding expressions V x 2 by the sum V 2 -f- &> 2 r 2 , and bring to the gain of the depression the algebraic sum 20 12 THE THEORIES AND PRACTICE OF Third, the movement of drawing in, which is a uniform rotation, creates the centrifugal force, which in its turn pro- duces a gradual increase of pressure from the ou'ie to the exterior circumference. If I isolate in imagination a pris- matic element of the air drawn in, placed at a distance x from the centre and presenting a height d x in the direction of the radius, a base S in the perpendicular direction, and a density 8, the mass in this element will be SdxB and the centrifugal force developed by the rotation Sd'xS , d F = --- o> 2 x. The increase of depression per unit of surface from one base to the other of this little prism will be got by dividing the preceding expression by S. We will divide again by 8, to have this pressure expressed as usual in the column of air, and we shall have finally for the differential increase of the pressure due to the centrifugal force , 7 d h = And integrating from x = r up to x = E, we shall have for a total difference of pressure from the circumference of the ouie to that at the outside of the vanes . a value to be carried to the credit of the depression produced by our ventilator. Our analysis is now complete, and we may make the CENTRIFUGAL VENTILATING MACHINES. 13 addition. Many terms, some positive and some negative, cancel themselves, and there will only remain, when designating by the letter u the tangential speed 55 cub. ft. 177-98 354-75 471-34 525-80 595-76 31676-78 125847-56 222163-19 276465-64 354929-98 in. 1-0303 0-9673 8976 0-8760 0-8543 in. 1-0228 0-9677 0-9114 0-8799 0-8342 in. + 0-0075 -0-0004 -0-0138 -0-0039 + 0-0201 Here the five points do not appear with the same perfec- tion as in that of Creal. Still the average straight line is exhibited with sufficient clearness. We may see by the numbers of the seventh column that the divergence exceeds hardly one-third of a millimetre. I may add that at Lalle the section for measuring is in a very inconvenient situation for observers, which will sufficiently explain the slight irre- gularity in the results. The equation for the average straight line is h = 1-0413 in. - -00000058 V 2 . Let us go, now, to the Guibal ventilator of Besseges, The experiments made on this machine are collected in the third table : I Equiva- lent Orifice. Speed of Rotation. Volume per Second. Square of Volume, X. Observed Depression, Calculated Depression. Difference. sq. ft. cub. ft. in. in. in. 1 3-921 76-39 187-32 35088-78 1 ' 1795 1-3042 -0-1247 9, 7-455 364-79 135269-26 1-2779 1-2763 +0-0016 3 20-914 J5 951-05 904496-10 1-0665 1-0681 -0-0016 4 25-521 fj 1114-00 1240986-00 0-9827 0-9764 + 0-0063 5 29-343 5 1225-15 1500992-52 0-8996 0-9059 -0-0063 30 THE THEORIES AND PRACTICE OF Here the four latter points range themselves in a straight line, having for their equation h = 1-3137 in. - -00000027 V 2 . The first point is certainly below this line. The variation is much too great to permit this to be attributed to any error in observation. Some experiments made before on the ven- tilator of Creal having always given me the same irregularity, I am led to assert as a fact that for very thin seams the depression is always below the mark which the results give for larger ones. If, putting the thing to an extreme, we shut completely off the gallery yielding the air to the ventilator, instead of the initial depression H, we find only a less value. Thus for the ventilator of Besseges 1 128 in. in place of 1 '313 in. To what can we attribute this depression, this shortcoming, if I may say so, of the depression in the case of thin mines ? The causes are numerous. A moment of reflection will enable us to discover them. As soon as we lower the movable shutter to accommodate the orifice of the outlet to the diminished yield, we transform this orifice into a straight rectangle, by which the air escapes in a thin stream. The perimeter friction increases in proportion to the section, and the loss of duty assumes a rapidly increasing importance. In the second place, the inclination which the vanes at their commencement present to the air so as to strike it without shock, only applies to a given yield ; with a circula- tion of air greater or less, there naturally follows a shock. In general this inclination is calculated for thick mines, and the useless effect, although unfelt, for average seams, rapidly increases for very thin ones, and helps to reduce the depression. At the same time, with thin seams it becomes certainly more difficult to obtain a flow with full mouth in the spaces CENTKIFUGAL VENTILATING MACHINES. 31 of the vanes and in the Guibal chimney a flow indispen- sable to realising the full restitution of the vis viva, in the manner of the ajutage of Venturi. This remark seems to be corroborated by the fact that in the case of thin seams the depression lacks absolute fixity : it is so vacillating that measurements taken at a few minutes' interval give quite different results. It follows from the preceding remarks that the straight line required by our theory cannot be followed up rigorously to the original ordinate. It bends when applied to very thin seams of from 4-304 sq. ft. to 5 '38 sq. ft. of equivalent FIG. 9. Square of orifice, as is shown in Fig. 9, the inflection beginning more or less quickly according to the machine. On the other hand, they seem to demand an indefinite continuation in the case of thick seams. This experiment on the Besseges ventilator shows it in fact as far as a mine of 29 '33 sq. ft. of equivalent orifice, a value rarely exceeded even in England. Mines having seldom if ever been found with less than 4 '30 sq. ft. of equivalent orifice, we may admit that within the limits met with in practice our theory is justified. I have not been able to utilise for the verification I seek the results obtained by the Commission with the ventilator of La Sagnette. This machine has a peculiarity which puts it outside of our theory. I said above that in covered ventilators 32 THE THEORIES AND PRACTICE OF the outlet constructed for the expulsion of the air should be regulated to the yield of the machine small with thin seams and larger for thick ones. At Besseges, with the aid of the moving slide, at Creal by taking away or adding deal boards to the cover, the Commission was able on each occa- sion to make this previous adaptation. At La Saguette the disposition of things did not adapt themselves to this : the orifice of outlet remained invariable, and would only suit, therefore, a particular mine. With seams thinner or thicker, and with these latter especially, considerable resistances arise, preventing the depression and yield from attaining the values we have a right to expect. The five points in this latter case did not range in a straight line ; the depression, at first feeble, gradually rose to a maximum for the state of mine for which it was intended. We may, then, with the aid of the numerical values which we have found for the constants H and M of our equation, determine the characteristic data of the three ven- tilators studied by us. I wish to speak of their manometrical result and of their orifices of passage. We have in effect the two following equations : H = ^, 0-65 o 2 20 If, taking the first of these equations, I give successively to H the three values obtained above, having taken care to ^ divide them by the proportion ^ of the densities of air and water, the following corresponding values of manometrical result will be obtained : For the ventilator of Besseges -691 Creal -572 Lalle -542 CENTKIFUOAL VENTILATING MACHINES. 33 These results fully confirm the theory that the Gruibal ventilator fitted with evasee chimney has the best results. That of Creal comes only second on the list, for its chimney is insufficient ; while the Lalle ventilator, which has neither cover nor chimney, necessarily comes last. We may, indeed, be astonished that this last machine reaches even so high a result. We have said above that a ventilator without a cover cannot obtain a result in mano- metrical effect superior to 50 ; but if we refer to the report of the Commission we shall find that this machine turns in a semicircular passage, which must certainly affect the yield in the same manner as a cover. I reach, then, the second equation and the data affecting M, and as I did to H, so the three values obtained in the course a of this paragraph must always be divided by -. From the o three equations which result I deduce for the orifice of passage o the following values : For the ventilator of Besseges 43-81 sq. ft. Creal 37-87 Lalle 30-02 The order of the orifices of passage is the same as that of the depressions, but we must not in consequence draw general deductions, for the theory will not warrant it. We understand in effect that the orifice of passage depends above everything on the construction and on the width which is given to the vanes and to the ouie, and to the section which allows the passage of the air. The Guibal of Besseges is 7 56 feet in width and 9 84 feet in the ouie. The ventilator of Creal is a large machine of 19*58 feet diameter and 11 '5 feet in the owe, but the width has been reduced to 3 6 feet. As to the ventilator of Lalle, 34 THE THEORIES AND PRACTICE OF the ouie is not more than 5 8 feet in diameter and the width from 4 32 feet at the axis to not more than 1 95 foot at the circumference. We find frequently in the industrial publications results of experiments made on ventilators with centrifugal force, especially since the impulse given by M. Guibal to machines of this class. The authors of these experiments have rarely taken the trouble to vary the resistance of the mine as was done by the Commission of Gard. In general they have only changed the speed of the ventilator, which, in virtue of the proportional law established, is equivalent to only one experiment. Such work cannot be utilised for the determination of the orifice of passage and manometrical result. I must, however, make an exception in favour of a study of great interest published in the Annales des Mines in 1860 by M. Tournaire. I reproduce the results obtained by him, but they only apply to the forge fan; still, it is in- teresting to show them in connection with large machines examined by the Commission. The ventilator of M. Tournaire was studied with the greatest care in its smallest details, excepting one point, which as we have seen above is of the highest importance it was not covered ; the air being driven out all round the circumference. It was 2*788 feet in diameter, and turned with a speed of 1500 to 1700 revolutions per minute, which gave a tangential speed of 219 to 250 feet per second. Nevertheless, to render these experiments comparable to those of the Commission, I have reduced them all to the tangential speed of 65 6 feet. This new table is drawn in the same manner as the preceding ones. The equivalent orifice which I show in the first column is nothing but the sum of the surfaces of the open orifices : CENTRIFUGAL VENTILATING MACHINES. 35 1 Equivalent Orifice. Speed of Rotation. Volume per Second. Square of Volume, X. Observed Depression, Y. Calculated Depression. Difference. 1 sq. ft. 2540 449-38 cub. ft. 8-94 79-92 in. 7551 in. 7645 in. -'0094 2 4230 14-48 209-67 7142 7185 + 0043 3 5069 17-34 300-68 6996 6862 + 0134 4 5435 19-95 398-00 6831 6512 + 0319 5 7610 24-86 618-22 7000 6520 + 0480 6 8450 26-03 677-56 5512 5521 -0009 7 9300 27-97 782-32 5134 5149 -0015 8 1-0462 29-77 886-25 4807 4779 + 0028 The first three points and the last three range themselves sufficiently near to a straight line, where the equation is h = -793- -000355V 2 . The two intermediate points place themselves above very distinctly. It is difficult to distinguish the causes which produce this difference, perhaps there exists a special yield for which the ventilator is particularly well proportioned. The constants of this straight line permit me to calculate, as for the preceding ventilators, the manometrical yield and the orifice of passage of this new machine. I obtain thus the two following values Manometrical yield -403 Orifice of passage 141 sq. feet. As the theory requires, the manometrical yield is inferior to 0*50. The addition of an eccentric envelope, following out M. Guibal's idea, certainly increases in a very great measure the compressing power of this ventilator. As to the orifice of passage, its lessened value is explained quite naturally by the small dimensions of the machine. Beyond the interesting data which I have given, I find no observations relating to the same degree of resistance to the circulation of air, or in other words to the same equivalent orifice. D 2 36 THE THEOEIES AND PRACTICE OF Data so incomplete do not allow us to arrive at a know- ledge of the orifice of passage or of the manometric yield, but for this latter we are enabled to obtain a value roughly approaching it, and which in default of any other may possess some interest and utility. The manometric yield, we have said, is the coefficient of reduction to be applied to the theoretical depression to obtain the initial depression before mentioned. If, in default of this latter, we are content with the effective depression observed under ordinary conditions, the result obtained will be very poor, and still more feeble as the seam ventilated is thicker ; but, in general, the difference of this approximate value will not be so considerable but that it may aid us in forming an opinion as to the exact value. Let us take, for example, the three ventilators of Besseges, Creal, and Lalle, studied by the Commission of Gard. The exact manometrical yields of these machines are respectively 0-691 .. 0-572 .. 0-542. If, instead of calculating the manometrical results with the aid of the initial depression, we use the effective depressions observed on the three mines of Besseges, Creal, and Lalle, we shall obtain " approximate results " 0-569 .. 0-524 .. 0-468. Without doubt the differences are very great, especially for the mine of Besseges, which is very thick ; but the order of these values approaches what is their true value, and, in default of more precise indications, they may suffice to compare different types of ventilators. It is with this idea that I have drawn up the table which follows. I have in- troduced all the ventilators, to the number of sixty, of which I have been able to procure any information. The approxi- mate result which is shown in the last column, is calculated, as we have seen above, by comparing the observed depression CENTRIFUGAL VENTILATING MACHINES. 37 with the theoretical expression where the expression is in water column W 2 g 7 *.' The error diminishes with thin seams, and increases with thick ones. I have taken into account the manometrical result as an important base for the examination of the equivalent orifice of the mine ventilated. The ventilators are given in the order of their perfec- tion. First, the primitive machines without a cover ; second, those simply covered without chimneys ; third, the machines covered, but with a chimney to a constant section ; and lastly, the Guibal, with a slide and cover and the evasee chimney. In each category the order followed is that of increasing diameters. Published experiments are rarely accompanied by atmo- spheric observations which permit a calculation to be made of the density of the air. I have allowed in each case for this density the average of 1-200 to 1000 for that of water. With these conditions the formulae which enable me to establish the numerical value of this table take the follow- ing simple form for the equivalent orifice 0-2V a = , Jh V being the volume given per second, and h the depression observed in inches of water. Second, for the theoretical depression N 2 D 8 _ ~ 800947' N being the number of revolutions per minute, and D the diameter of the machine in feet. Third, and consequently, for the manometrical yield _ 800947 h N 2 D 2 Sometimes the observation of the yield has been defective, and then the equivalent orifice could not be determined. 38 THE THEOKIES AND PRACTICE OF TABLE FAN " 1 )imensions. No, Date. Mine. Exterior )iameter. Diameter of Oufe. Width. ft. ft. ft. 1 2 June 25, 1842 Mar. 28, 1844 Shaft No. 5 of Grand Hornu . . Ditto 5-57 5-57 4-46 4-46 1-11 I'll 3 May 24,1844 Pit No. 2 at Sauwartan 6-56 5-21 1-31 4 Apr. 23, 1847 At Pit St. Caroline of the Colliery of St. Victor Frameries. 6-26 5 6 June 28, 1849 June 1, 1843 Shaft No. 1 at Escouffiaux Colliery . . Pit No. 3 at Marcinelles 5-57 6-62 3-28 2-06 3-93 1-96 7 8 Oct. 4, 1842 Oct. 1, 1849 Pit No. 3 of Agrappe and Grisceil, at Frameries. Bayemont Colliery 8-29 8-52 4-26 4-48 3-21 3-77 9 10 June 20, 1849 Jan. 7, 1848 Shaft No. 3, Grand Trait, of Agrappe and Grisceil, at Frameries. Shaft called No. 12 at Agrappe, Noir- chain Colliery. 9-05 9-05 4-92 4-92 4-92 4-92 11 Nov. 28, 1848 Large Seam of the Epinois Wood and Elouges Colliery. 9-18 4-59 3-93 12 13 14 Oct., 1847 Nov., 1847 July 30, 1863 Shaft No. 5 (St. Barbe) at Escouffiaux Colliery. Shaft No. 7 (St. Antoine) at Es- couffiaux Colliery. Great Seam of the Epinois Wood at Elouges. 9-38 9-38 9-84 4-59 4-59 3-93 3-93 4-10 15 Nov. 20, 1842 Shaft No. 1 at Grand Picquery Col- liery, Frameries. 10-00 4-78 3-24 16 17 18 Nov. 25, 1842 Apr. 30, 1865 Pit Ste. Caroline of St. Victor Colliery, Frameries. Crachet and Picquery Pits, Shaft St. Placide. Shaft No. 12 at Marcinelles Colliery . . 10-29 22-96 21-32 5-24 9-84 7-38 3-11 5-57 4-59 19 Ormont Colliery at Chatelet 26-24 4-59 CENTRIFUGAL VENTILATING MACHINES. 39 No. I. UNCOVEKED. Publications. Authors. Equivalent I Orifice. i& rill Remarks. sq.ft. Memoir on Apparatus G. Glepin 1-88 132 Type, Combes ; vertical dia- applied to Ventila- ting Mines, p. 58. meter, 1 ouie, 3 vanes. Ditto, p. 58 Ditto 3-56 090 Ditto. The mine being in- creased the yield is diminished. And also the manner Ditto 2-94 173 .. of working at Combes, Vol. II.. p. 491. Ditto, p. 63, & Combes, A. Cabany 5-54 400 Ditto; horizontal axis, 2 p. 499. Notes by M. ouies, 2 vanes. Type, Leto- Cabany. ret ; a well-constructed fan, but rather small. Ditto Ditto 4-22 476 Ditto. Memoir on Apparatus G. Glepin 3-70 121 Ditto, 2 ouies, 8 vanes, in sheet applied to the Venti- iron, slightly curved. lation of Mines. Ditto, p. 49.. .. .. Ditto 3-65 438 Ditto ; vanes inclined at 110 to the radius, 2 ouies. Annals of Public Works Jochams 2-91 323 Ditto ; 4 vanes at an angle of in Belgium, Vol. XL, 130 to 150. p.l. Notes by M. Cabany . . A. Cabany 8-01 393 Ditto. Very strong inclination of vanes. Ditto Ditto 9-82 303 Ditto. Average of 11 experi- ments made with assistance of MM. Toilliez, Albert, Harnel, and Toilliez, J. Annals of Public Works Jochams 4-11 285 Ditto. in Belgium, Vol. XL, p. 1. Notes by M. Cabany . . A. Cabany 4-13 474 Ditto. Ditto Ditto 4-40 377 Ditto. Vanes at 110. Annals of P ublic Works Hamal and 51-43 368 Ditto. in Belgium, Vol. Schorn. XXIL, p. 5. Memoir on Apparatus G. Glepin 2-926 163 Ditto. Vanes curved, follow- applied to the Venti- ing a surface inclined to the lation of Mines, p. 50. radius of 137 to 153. Ditto, p. 46 Ditto 3-109 354 Ditto. Vanes inclining to 135. Five experiments. Ventilation of Mines, Gille and Fra- 8-661 496 Type, Guibal, before covering. by M. Devillez, p. 227. neau. Supplement to Account 7-661 439 Type, Lambert ; 6 radial vanes. of Working, by Pon- Of two experiments I have son, Vol. L, p. 395. chosen the most favourable to the machine. Ventilation of Mines, Devillez, Le- 8-199 455 Ditto ; 8 radial vanes. by M. Devillez, p. 181. toret, Delhaise and Gilbert. 40 THE THEORIES AND PRACTICE OF TABLE No. I. (continued). COVERED Dimensions No. Date. Mine. Exterior Diameter. Diameter of Oule. Width. ft. ft. ft. 20 Nov. 5, 1876 Grand Combe Mines, La Sagnette Fan 9-18 4-39 3-93 21 99 Aug. 10, 1859 Fi-ftTtj Aiig to Grisoeil Colliery, No. 10 Ditto 13-12 13-12 5-24 5-24 5-01 5-01 Oct., 1859. 23 July 25, 1861 Escouffiaux Colliery 13-12 24 25 June 23, 1861 May 28, 1865 Basse Sambre Colliery Crachet and Picquery Collieries, Shaft St. Placide. 13-12 22-96 9*84 5-57 26 27 28 Feb. 19, 1859 Mar. 22, 1859 Jan. 7,1865 COVEI Jean Bart, Cie. d'Anzin Ditto IED FAN 11-80 11-80 13-12 9 WITH C 5-24 5-24 6-56 HIMNEY 4-92 4-92 4-92 Stiring Mines, Pit St. Joseph .. .. 29 Grand Buisson Colliery, Shaft No. 3 22-96 9-84 5-57 30 Society of Hornu Wasmes 29-52 9-84 3-28 31 COVERED "\ Sainte Hortense at Paturages ^ENTlLAl 13-12 rORS, WIT! 6-56 [ SLIDE 4-92 32 June 25, 1862 Verger, Cie. d'Anzin 16-40 8-200 6-56 33 Aug. 11, 1861 Grosse Fosse, Cie. d'Anzin 16-40 8-200 6-56 34 Montceau- Fontaine, Charleroi .. 19-68 CENTRIFUGAL VENTILATING MACHINES. 41 FANS WITHOUT CHIMNEY. Publications. Authors. Equivalent Orifice. Approxi- mate Ma- nometrical Result. Remarks. sq . ft. Minutes of the Mineral Ventilation 7-132 638 This quantity follows from the Society, Vol. XII., Commission second experiment of the p. 533. of Gard. Commission. The other four gave a less quantity. Annals of Public Works Hamal and 12-95 429 The nine experiments show an in Belgium, Vol. Gille. action sufficient to destroy the XXII., p. 5. regularity of the results. Supplement to Account Ditto 13-17 505 Concerns, no doubt, the same of Working, by Pon- fan as above. Experiments son, Vol. I., p. 384. do not agree. Ditto Gille 682 E xperiments agree but slightly. The quantity not having been measured the equivalent ori- fice remains unknown. Ditto Masy . , 613 Same observations as above. Ventilation of Mines, Gille and 9-50 491 Same fan as at No. 17. The by M. Devillez. Franeau covering has been put on but not the slide or the chimney. OF CONSTANT SECTION. Notes by M.Cabany.. Ditto Minutes of the Mineral Society ,Vol.X., p. 437. Ventilation of Mines, by M. Devillez, p. 236. Ditto, p. 253 .. .. Ventilation, by Devil- lez, p. 221. Manuscript Notes, M. Cabany. Ditto Supplement to Treatise on Working by Ponson. A. Cabany 12-00 583 First Guibal type, with the slide in a groove. The chim- ney square from 4-92 feet. Average of two experiments most favourable to the machine. Ditto 17-49 352 Ditto. The mine being very thick explains the diminution of result. Laigneaux and 10-01 284 Ditto. The chimney square Distinghin. from 4-37 feet. We do not see the cause of so poor a result. .. 43-36 626 Ditto. The chimney has not yet its evasee slope in the interior. 609 Special type. The chimney has from top to bottom a uniform section of 6-56 feet by 5-9 feet. ;GUIBAL TYPE). 570 Yield not given. Equivalent orifice unknown. Atkinson, Dickenson,and 8-57 651 Experiments agree, and are good. Greenwell. A. Cabany 17-56 633 Eesult high, regarding thick- ness of seam. * * 6-56 595 42 THE THEORIES AND PRACTICE OF TABLE No. I. COVERED VENTILATOES, WITH SLIDE ] Dimensions. No. Date. Mine. Exterior )iameter. Diameter of Oule. Width. 35 Apr. 22, 1866 ft. 19 '68 ft. 9 '84 ft. 36 37 July 31, 1865 Mar 25 1866 Crachet and Picquery Ditto 22-96 22 '96 9-84 9-84 5-57 5-57 38 S tiring . . 22 '96 9*84 5*74 39 22-96 9-84 5-57 40 .. Grand Buisson 22-96 9-84 5-57 41 Sep. 11, 1870 Grand Mambourg 22-96 9-84 8-20 42 AO 1866 1865 Nceux (Pas de Calais) Els wick 22-96 22'96 9-84 9 -84 5-57 fi-23 44 45 46 July 24, 1869 Feb. 14, 1869 Von der Heydt. Herne-Bochum, West- phalia. Rhein-Elbe, Westphalia Montceau-Fontaine 29-52 29-52 29-52 9-84 9-84 47 -.. United Collieries at Charleroi 29-52 9-84 5-57 48 49 Oct. 24, 1869 Colliery of Grand Mambourg at Mon- tigny-sur-Sambre. Colliery of Rieu t)u Cceur 29-52 29-52 13-12 9-84 6-56 6-56 50 51 52 May 17, 1869 June 21, 1869 1865 Colliery of La Louviere Colliery of Grand Buisson Pelton Colliery, Durham 29-52 29-52 29-52 9-84 9-84 13-12 6-56 6-56 9-84 53 Apr. 20, 1867 Middle Duffryn Colliery, S. Wales . . 29-52 .. 9-84 54 Mar. 2, 1868 Gethin Colliery, S. Wales 29-52 9-84 55 Colliery Lwynpia, S. Wales 29-52 .. 9-84 56 57 Ebbw Vale, S. Wales .. Colliery of Trieu-Kaisin 39-36 39-36 9-' 84 11-8 9-84 58 Mar. 25, 1877 Colliery of Crachet and Picquery 39-36 13-12 8-2 CENTKIFUGAL VENTILATING MACHINES. 43 AND EVASEE CHIMNEY (GuiBAL TYPE). continued. Publications. Authors. Equivalent Orifice. Approxi- mate Ma- nometrical Result. Remarks. sq. ft. Ventilation, by Devil- Stoesser and 10-16 642 lez, p. 239. others. Ditto, p. 229 . . Gille and 8-98 654 Same as Nos. 17 and 23. Franeau. Machine complete. Ditto, p. 240 .. .. Stoesser and 6-80 728 No doubt the same machine. others. The increase in yield may be attributed to less equivalent orifice. Ditto, p. 221 .. .. . , 598 Particulars are incomplete. Ditto, p. 221 .. .. .. .. 579 Ditto. Ditto, p. 236 . . 4-33 711 Same as No. 29. Interior circu- lar casing in chimney complete. Ditto, p, 237 .. .. De Poitier, 11-14 628 The great width of this machine Havrez and has no effect on result. Halley. Unknown C. Brice 9-12 633 Communicated by M. Brice. North of England W. Cochrane 20-15 590 Ditto. Inst., Vol. XIV. Annales des Mines, Extracted by 14-72 684 Ditto. 1873, p. 297. M. Voisin. Ditto Ditto 15-83 673 Ditto. Supplement to Treatise by Ponson, Vol. I., Atkinson and Dickenson. 13-78 751 Volume of air in these experi- ments is very irregular. p. 374. Ventilation of Mines, 583 The details are very incom- byM. Devillez,p.221. plete. Ditto, p. 21 545 Ditto. Ditto Brunier 11-41 665 The two first experiments Ditto, p. 237 .. .. Eoger 8'38 675 differ ; the seven others agree. Ditto. Ditto, p. 238 .. .. x, its square Vj 2 may be replaced by the sum I may, then, bring to the credit of the depression the algebraic sum Third, The air reaching the upper level of the moving wheel is thrown out with the speed V 3 , which is the resultant of the relative speed of outlet V 2 and of the speed of drawing in &> x. The parallelogram of these speeds gives for V 3 the known expression, Y 8 2 = y 2 2 _|_ W 2 38 _ 2 V 2 CO X COS a, a being the angle which the vane makes with the upper level. Animated by this speed V 3 the air enters the diffuser ; like the Guibal chimney the evasee passages of the diffuser gradually extinguish this speed, and if W represents the value which it possesses at the outlet, the restitution CENTRIFUGAL VENTILATING MACHINES. 51 of pressure will be always, according to the theory of Bernoulli!, .Replacing V 3 according to its value as a function of its component parts, I have to carry to the effective side of the depression, the sum, Vg 2 o)V 2Y 2 o>acosa W* h 2^ + ^' -27 Here the centrifugal force, acting perpendicularly to the trajectory of thin streams of air, cannot produce any increase in the depression. There remains then only to make the addition of the values (1), (2), (3) which gives, when all reductions are made, o>V 2 V 2 9 9 and it approaches still nearer to this latter as the dia- phragm or central newel is enlarged. Now we cannot increase this diaphragm without reducing at the same time the orifices of passage and lowering in proportion the effective depression; but this danger diminishes with thin seams, and we can understand that at its limit we must admit for the theoretic value of the depression in the perfect ventilator that which corresponds to the exterior radius, *& H.= , and since w K is the tangential speed which we have expressed CENTRIFUGAL VENTILATING MACHINES. 53 up to this time by the letter u, Jj.0 LZZ 9 g an expression identical with that found for ventilators with centrifugal force. From that we shall pass to the initial depression, with the aid of a coefficient of reduction, g' in which the value, more or less high, forms the mano- metrical result of the machine : with this exception, that to different causes which reduce the result we must add the difference of force which exists in practice between the interior and the exterior radius. Thus there is but one and the same theory for all depri- mogen ventilators without exception. For machines with direct force as for those with centrifugal force, the power of depression is connected with the tangential speed, the power of yielding volume to the orifice of passage by identical expressions. For the one as for the other the effective depression and the volume yielded result from two formulae which I shall here repeat h - s-> V = . ('+) I have not found in any industrial works experiments sufficiently complete to allow me to make a calculation with sufficient exactness of the manometrical result and of the orifices of passage of a ventilator by direct impulsion. I will content myself, then, by giving, as I did for centri- fugal ventilators, a table of manometrical results drawn up with the aid of all the experimental data relating to these machines that I have been able to procure. THE THEOKIES AND PRACTICE OF TABLE No. Date. Mine. Dimensions. Exterior Diameter. Diameter. Height. ft. ft. ft. PNEUMATIC SCREW 1 2 3 1842 Apr. 18, 1842 No. 2 Pit, Monceau-Fontaine Ditto 2-624 2-624 3-936 095 095 2-624 2-624 Colliery of Chatelet 4 5 July 7, 1843 Nov. 2, 1849 Colliery Sauwartan-sur-Dour Colliery of Pieton-Campagne 4-59 6-56 150 3-18 3-39 3-28 6 7 8 July 23, 1849 Ditto June 1, 1843 Colliery of Monceau-Fontaine Ditto 7-216 7-216 9-84 5-576 5-576 196 3-60 3-60 2-624 Colliery of Trieu-Kaisin VENTILATORS WITH HELICOIDAL 9 10 11 May 31, 1843 June 18, 1843 July 23, 1848 Colliery of Poirier Ditto 5-576 6*56 7-54 1-968 1-64 4-26 3-54 3-93 918 Colliery of Vivier-du-Couchant 12 13 14 15 16 17 18 Aug. 14, 1849 Ditto Oct. 26, 1848 Nov. 2, 1848 Colliery of the Reunion at Mont-sur- Marchienne Ditto 7-20 7-20 7-20 7-20 jATORS T 8-72 8*72 8-85 3-412 3-412 5-57 5-57 PITH VAN 918 918 918 623 623 656 656 ES OF A Ditto Ditto VENTII Grand-Bac Ditto Colliery of Val-Benoit, near Liege . . VENTILATORS WITH HELICOIDAL 19 Aug. 2, 1860 Mines of Bethune, at Bully-Grenay . . 8-20 3-28 CENTKIFUGAL VENTILATING MACHINES. 55 No. II. Publications. Authors. Equivalent Orifice. Approxi- mate Ma- nometrical Result. Remarks. sq. ft. OF M. MOTTE. Memoir on Machines G. Glepin 3-583 050 Two helicoidal slides. This applied to Ventilation screw is the first constructed. of Mines, p. 42. Annals of Belgian Pub- Gonot 2-872 084 The same machine. The mine lic Works, Vol. L, being narrowed, the result is p. 236. better. Memoir on Machines Glepin 1-883 121 Two helicoidal slides. applied to Ventilation of Mines, p. 40. Ditto, p. 40 Ditto 3-034 183 Ditto. Annals of Belgian Pub- Jochams 3-72 208 Ditto. lic Works, Vol. XI., Ditto Ditto 6-197 189 Ditto. The machine is fitted with diaphragms which make the air enter at the centre and leave at the circumference. Ditto Ditto 3-292 230 Ditto. The mine had been artificially narrowed, which improved the result. Memoir on Machines Glepin 6-442 199 Ditto. An inverse current applied to Ventilation of Mines. was produced towards the centre of the machine. VANES, BY M. PASQUET. Memoir on Ventilating Glepin 7-85 117 Three vanes in a conical form. Machines, p. 64. Ditto, p. 68 Ditto 2-162 120 Six vanes, same contraction as last. Annals of Public Jochams 4-529 188 Type, Pasquet modified. Works, Vol. XL, p. 1. Ditto Ditto 6-56 131 Ditto. Helicoidal passage. Ditto Ditto 4-163 182 Same machine. The mine being narrowed increases the result. Ditto Ditto 7-42 123 Ditto. Ditto Ditto 3-658 197 Ditto. The mine being reduced increases the result. WINDMILL, BY M. LESOINNE. Treatise on Working Trasenster 13-66 080 Six vanes inclined to the of Mines, by POD son. centre. Ditto Cabany 15-49 069 The mines were large, giving a bad result. Ditto .. Trasenster 10-32 131 Ten vanes inclined through the whole length. VANES, BY M. DAVAINE. Annals of Mines, Vol. Sens 4-633 161 Four vanes of wood, forming XVIL, p. 425. a screw. 56 THE THEORIES AND PRACTICE OF The results in this table are all very feeble. The highest does not exceed 0*230. We must not be astonished, for none of" the machines named realise the conditions which are so clearly required by the theory ; none of them have their vanes straightened to the plane of the axis, and they do not throw out the air into a diffuser. Another cause occurs to still further diminish the result obtained the insufficiency of the orifice of passage. The largest of these ventilators is no more than 9*84 feet diameter, and so, if we deduct from that the surface occupied by the diaphragm or the central spindle, there remains only a very narrow passage, which absorbs in pure loss a great part of the depression, We see this at once if we reduce or enlarge the equivalent orifice of the mine ; at the Pit No. 2 of Monceau-Fontaine (Nos. 6 and 7 in the table), a small reduction suffices to increase the result from 0*189 to 0*230. It is the same at the colliery Keunion (Nos. 14 and 15), where, from the same cause, the result rises from 123 to * 197. These observations warrant the assumption that if the average of the " approximate results " in our table attains to 0*145, the exact manometrical result, based on the initial depression, would certainly exceed 300. It is impossible to say which is the best of the four types of ventilators examined, for our. observations were neither sufficiently regular nor sufficiently numerous to demonstrate a marked superiority. The only thing which appears to be at all clear is that the large diameters are favourable to yield. It was to such machines as this that recourse was had for the purpose of ventilating the large hall at the Palace of the Trocadero for fetes. In the excellent communica- tions made by M. Bourdais to the Members of Congress at Paris, he said that they obtained very remarkable results with the employment of machines of the helix type. Are these facts, then, in opposition to what I have shown? CENTKIFUGAL VENTILATING MACHINES. 57 I think not. The truth is that the ventilation of a large hall is incomparably more easy than that of a mine. It is sufficient for M. Bourdais to have a pressure of 23 inch of water in order to obtain a circulation of 2000 cubic feet of air per second, but these figures correspond to an equivalent orifice of about 97 square feet. Besides, the work was divided between two machines, each of which had no more than 0'12 inch of pressure to produce. Under such conditions we may say that all ventilators are good, provided that they possess a sufficient orifice of passage. The motive power required is the smallest possible; its economy becomes a secondary consideration ; and one is naturally led to choose the most simple machine, the least cumbersome, and especially the least noisy. It appears from these considerations that ventilators by direct impulsion whilst good for ventilating buildings, could only give very feeble results upon collieries. Is it then possible entirely to proscribe them ? I would not say so. Up to the present time there has been so little regard paid in their construction to the requirements of theory, that we may hope that with more intelligent arrange- ments we may approach as high results as a Guibal ventilator. Besides, these machines possess in some respects an important advantage, which, under certain circumstances, might lead the balance to be given in their favour: they do not occupy in the plane perpendicular to their axis, an area greater than their exterior circumference. To fully understand this advantage, we must assume for a moment that under certain circumstances we might have to place a ventilator within the mine. A Guibal would require an enormous space, not only for its circumference but for the eccentricity of its cover and chimney. A ventilator by direct impulsion would only require a circular chamber equal to that of its vanes. 58 THE THEORIES AND PRACTICE OF This hypothesis of a ventilator below the surface, if it has never yet been, might still be realised. Constantly we see in mines currents of water descending unutilised from great heights to reach the sump. Would it not be rational to utilise this force to turn a turbine placed on the axis of a ventilator ? 5. MOTIVE POWER. To complete the theoretical study in which we are engaged, it remains for us to determine the motive power necessary to drive the depriinogen ventilators. I mean by motive power the work to be applied to the shaft of a ventilator to set it in motion. Suppose, then, a deprimogen ventilator attached to a mine where the equivalent orifice is known, and turning with a given tangential speed. To determine the exact condition, let us suppose that it is a centrifugal ventilator, and that its vanes are bent in the direction of the radius as theory requires, what would be the motive power required by this machine ? If we wish to make this determination by rational and direct method, it will be necessary first to establish a polygon of acting forces for any element of the profile of the vane ; then to project the resultant on the trajectory of the element ; to multiply this projection by the space passed through ; and then to pass by an integration of the element to the entire vane. I will content myself here with the following a posteriori method : Let us admit for a moment that our ventilator is a perfect machine, as we have often done during this study. The result will be 100 for 100 ; or, otherwise, the motive power shall be equal to the power utilised, and as this latter is obtained it follows as a well- CENTKIFUGAL VENTILATING MACHINES. 59 known rule in multiplying the volume by the depression that I have for the motive power the simple product H being the theoretical depression expressed in inches of water and V the corresponding value. If, now, we call to mind machines more or less imper- fect, the observed depression will be notably inferior to the theoretical value H , and the volume afforded reduced in proportion. But recalling what was said when we com- menced we shall remember that this diminution is only apparent the imperfect ventilator developed the theo- retical depression equally as well as the perfect ventilator, only that a certain portion of this depression was absorbed by frictions, losses of duty, and other imperfections in the machine. In the first of the two factors of motive power H there is no change ; the second V becomes the effective volume given, V. Now add the work of passive resistance inherent to every machine made by human hands, and we shall have for the expression of effective motive power Thus the motive power to be applied to a ventilator with centrifugal force and with radial vanes is equal to the product of the theoretical depression by the volume yielded, increased by the work of passive resistance. All the terms of this expression may be easily calculated in advance, or at least with an approximation sufficiently accurate for the constructor. The theoretical depression for ventilators with radial vanes, expressed in inches of water, is given by the formula 60 THE THEORIES AND PRACTICE OF We shall find in the additional note (E), a table of the results of calculations, in which this depression is given for all practical values of the tangential speed. When the vanes are inclined to the radius, the value of the theoretical depression is modified a little and becomes U? 8 u V 2 cos a $ H = 9 9 V 2 being the relative speed of the air leaving the vanes. It is modified in the same way for ventilators by direct impulsion, or, correctly speaking, the theoretical depression is due not to the tangential speed, but rather to the speed of a certain average point, of which the distance from the axis has for its value _ But the superiority of the ventilators with centrifugal force and the radial vanes appears to be generally recognised, so that the first expression of H is alone necessary. The knowledge of the volume given V results, either from the formula established above, or from a simple hypothesis. As to the passive resistances they are of two kinds, easily determined by methods familiar to engineers, viz. : The friction of the shaft on its bearings ; and The friction of the air drawn in by the vanes against the fixed sides of the ventilator. For this latter friction it is well to observe that of the two components of the air moving in the machine, one only interests us, that which follows the direction of the circum- ference described by the vanes. The component parallel to the radius need not in effect increase any resistance to the load of the propulsive vane, since it is perpendicular CENTRIFUGAL VENTILATING MACHINES. 61 to its movement. This fact much simplifies the matter, for it permits us to reduce the complex movement of the air to a simple rotation round the axis, as in the case when the mine is shut off and the air turns in its place. Thus the calculation limits itself to measuring the fric- tion surfaces, estimating the average speed of friction, and applying to these data the coefficient of friction based upon experimental knowledge, in which, according to Aubuisson, the value will be equal to about '0032. To these two frictions the passive resistances are reduced, which affords the work to be applied to the shaft of the ventilator. But if we mean by the motive power the work of the steam acting on the piston of the machine as it is measured with the indicator of Watt, it is necessary to add to the passive resistances all the shocks and frictions on the part of this machine, not forgetting the important work absorbed by the belt where this kind of transmission exists. I have insisted on a simple means of motive power being employed by constructors in this calculation, because they often employ for this object very fantastic methods. I may cite amongst others that which consists in taking for the work of opposing forces the product of the depression by the surface of the vane, but this method is doubly erroneous, for it neglects the yield, which is one of the factors of work, and introduces the surface of the vane, where the influence is nothing. We may remark, however, that the motive power in- creases rapidly when we increase the speed of rotation of the ventilator, the volume V varying as the simple speed, the depression H as its square, and the first term of the work of the motor, and also the most important, VH increasing as the cube of the speed. So it is less easy to make this latter vary within large limits than might 62 THE THEORIES AND PRACTICE OF at first sight appear. If, on the contrary, we suppose the speed of rotation to be invariable, H becomes constant, and the motive power depends only on the yield V. This has the singular effect, which at first appears almost para- doxical, that the more we increase the resistance to the passage of the air, the more the work is reduced, and the ventilator increases in speed. And if, on the contrary, we give the air free access to the machine, the work becomes greater, and the speed of the ventilator is reduced. We observe just the reverse with the volumogen ventilator. The expression that we have now to find for the engine power to be applied to deprimogen ventilators enables us to establish the mechanical yield of these machines. I say mechanical in opposition to the manometrical useful effect, of which we spoke just now. We know the work useful effect ; it is the product V h of the effective volume by the effective depression ; the motive power is yet to be deter- mined. Then the mechanical yield is the proportion of useful work to the motive power and it takes the form We may replace in this expression the quantities V^ and Ho by their values in a function of the given characteristics of machines and of the mines which they ventilate (equivalent orifice, tangential speed, &c.), but the term T p of the deno- minator not admitting of reduction, we should have a com- plicated expression, and consequently not to the point. We may also with the slightest reflection observe in the pre- ceding expression the influences of different kinds which vary the results. We may ask, for example, what becomes of the mechanical yield of a ventilator, when we increase its speed of rotation. The useful work V h and the first term V Ho of the motive CENTRIFUGAL VENTILATING MACHINES. 63 power will both increase as the cube of this speed, so that if we can admit that the term T p of passive resistances in- creases with the same rapidity, the yield will be obtained independent of the speed. But in reality the term T p increases much less quickly, hence the yield improves as the speed increases. This is proved by different experiments where care has been taken to vary the speed of the ventilator. I may cite, for instance, the numberless experiments made by MM. Grille and Franeau on the G-uibal ventilator of Crachet, to be found in the treatise on ventilation by M. Devillez, page 227. If, supposing the speed of rotation to be invariable, we increase the equivalent orifice of the mine from zero to infinity, we shall find at first no result, the useful effect being nothing itself. Beyond, the result increases by degrees, but remains feeble in consequence of the importance of the term T p of passive resistance. In proportion as this influence weakens the yield and the result continue to increase. But then there occur rapidly increasing frictions of the air traversing the machine ; quickly this new influence predominates, and having reached a certain maximum the yield begins to decrease, and finally attains a point where it becomes nothing. This work of the yield is very clearly shown by the experi- ments of the Commission of Gard, to which I refer the reader. It shows that for every deprimogen ventilator there corres- ponds a given mine for which its yield is greatest, and to which it is especially appropriate. As to the influence of the manometrical yield, and of the orifice of passage, it is easy to see that the mechanical yield varies in the same direction as these. When they are weakened, it is because the frictions, losses of quantity, and other imperfections increase, all causes which assist to weaken the yield. The experiments made to measure the mechanical yield of 64 THE THEORIES AND PRACTICE OF ventilators are much less abundant than those which are limited to measure the yield and depression. In many cases they have sought to establish the motive power by applying to the surface of the piston the pressure observed on the boiler gauge; but this method is based on the employment of coefficients more or less arbitrary, and does not appear to me to merit any confidence. I cannot admit as important data results not obtained with the aid of the Prony friction brake, or of the Watt indicator. The use of the former is much more limited than the latter, besides it supposes that we may break the connection between the power and the resistance, a circumstance which does not happen except in machines where the motive power is trans- mitted by a belt. These inconveniences are unfortunate, for, from the point of view of results, the brake presents a great advantage over the indicator. It measures exclusively work transmitted to the shaft of the ventilating machine, whilst the indicator includes at the same time all the passive resist- ances of the motive power ; the numbers obtained in the result will be different also according to the instrument for measure- ment to which we have recourse, they will be weaker with the indicator in consequence of the exaggeration of the term T^, of passive resistances. I have included in the table on pp. 66-69 a certain number of observations of yield selected from industrial works. In general the observations are repeated a certain number of times for each machine, varying sometimes the speed and sometimes the resistance of the mine, and I have reproduced the minimum and maximum results in the table. The signification of these numbers varies with the dynamo- meter employed ; I have been careful to specify this latter in the column observations. The ventilators by direct impul- sion are placed at the head of the table in order to follow as nearly as possible the order of increasing yield. CENTRIFUGAL VENTILATING MACHINES. 65 As we may see (Table III.), the ventilators by direct impulsion give only a very poor mechanical result ; the highest deduction being made for passive resistance, it does not exceed '824. The ventilators without cover present some very irregular results, the cause of which is not clearly seen. Thus it is surprising that the ventilator of Crachet, which is 22 96 feet in diameter, does not exceed 22, whilst the turbine of Lalle rises to 47. We may see from these results that if there has been any progress with ventilators by direct impulsion the advantage gained is small. This progress continues pretty equally with covered ventilators, from ventilators with rectangular chimney up to ventilators properly called Guibal, which are at present the most efficient. If we take as a characteristic of the yield of each type of ventilators the arithmetical average pure and simple of the figures shown in our table, we shall obtain the following series : Ventilators by direct impulsion 260 by centrifugal force, without cover . . 278 with centrifugal force, covered, without chimney 0-284 Ventilators with centrifugal force, with cover and rectangular chimney 0'379 Ventilators with centrifugal force, with cover, slide, and evasee chimney 0'467 Certainly it is rather the order of these values than their absolute magnitude which we should consider here ; but even with this reserve the series is still very interesting and explicit. The most important of these averages is that of the Guibal ventilators, for they result from a number of already important observations. Still I think it rather poor compared with the minimum of our table results in general, though this may be a consequence of taking observations F 66 THE THEORIES AND PRACTICE OF TABLE No. Date. Mine. Dimensions. Exterior Diameter of Diameter. Ouw. Width. ft. in. ! ft. in. i ft. in. VENTILATORS BY Apr. 7, 1843 Aug. 2, 1860 Motte screw, at No. 1 Pit, Sauwartan- sur-Dour. Davaine's Ventilator, with helicoidal vanes, at Bully-Grenay. 4. 7'1 1-8 6 6-7 3-9 2 4-7 UNCOVERED VENTILATORS BY Mar. 28, 1844 , Combes' Ventilator, Grand Hormi .. ! 5 6-9 Nov. 25, 1842 , Letoret Ventilator, Colliery of St. Vic- toire, at Frameries. Sept. 24, 1876 ' Turbine Ventilator, Mines of Lalle and Apr. 30, 1865 10 3-6 12 5-6 Guibal Ventilator, Colliery of Crachet 22 11-5 and Picquery. Lambert Ventilator, Ormont Colliery, 26 2 9 at Chatelet. 4 5-511 1-4 5 3-013 0-6 4 4-7 9 10-1 4 1-2 4 7-1 4 7-1 Aug. 10, 1859 Nov. 28, 1865 COVERED VENTILATORS, WITHOUT Grisceil Colliery, No. 10 Pit .. .. 13 1'4 5 3-0 j 5 0'2 Guibal Ventilator, Crachet and Picquery 22 11-5 9 10-1 4 7-1 COVERED VENTILATORS WITH 10 11 12 Mar. 22, 1859 July 29, 1877 Jean Bart Pit .. .. Creal Mines, Besseges . Grand Buisson Colliery 11 9-71 5 3-0 19 8-211 5-8 22 11-5 9 10-1 4 11-0 3 7-3 5 6-9 CENTRIFUGAL VENTILATING MACHINES. 67 No. III. Publications. Authors. Manometric Yield. Observations. Min. Max. DIRECT IMPULSION. Memoir on Ventilating Machines. Glepin 0-220 0-230 Prony brake. Annales des Mines, 1860, p. 425. Sens, Mining Engineer. 0-264 0-324 Watt indicator, motor with- out load deducted or the result would not exceed 0-253. CENTRIFUGAL FORCE. Treatise on Mine Work- ing, by Ch. Combes. Glepin 0-270 0-290 Prony brake. Memoir on Ventilating Machines, p. 46. Ditto 0-160 0-180 Ditto. Bulletin of Society of Mineral Industry, 2nd Series, Vol. VII., p. 477. Aguillon, Fumal, and Murgue 0-277 0-470 Watt indicator, by Commission of Gard. Ventilation of Mines, by M. Devillez, p. 227. Gille and Franeau. 0-160 0-220 Type, Guibal, before covered. being Ditto Devillez and Letoret, &c. 0-354 0-398 Prony brake. CHIMNEY, BY CENTRIFUGAL FORCE. Annals of Public Works, Belgium, Vol. XVII. .. 0-267 0-390 Watt indicator. Ventilation of Mines, by Devillez, p. 228. Gille and Franeau. 0-170 0-310 Ditto, same as No. 6. CHIMNEY OF CONSTANT SECTION. Notes of M. Cabany. A. Cabany 0-334 0-342 Ditto, Guibal, early type. Bulletin of Society of Mineral Industry, Vol. VII., p. 477. Aguillon, Fumat, and Murgue. 0-422 0-517 Ditto. Part of work restored by a canal vasee. Ventilation of Mines, by Devillez. 0-320 0-334 Ditto, Guibal, but the chim- ney of constant section. 68 THE THEORIES AND PRACTICE OF TABLE No. Date. Mine. Dimensions. Exterior Diameter. Diameter oi Ou'ie. Width. i ft. in. ft. in. ft. in. COVERED VENTILATORS WITH SLIDE AND 13 June 25, 1862 Verger Pit, Anzin 16 4-8 8 2-4 6 6-7 14 Aug. 11, 1861 Grosse-Fosse, Anzin 16 4-8 8 2-4 6 6'7 15 July 22, 1877 Grangier Pits, Besseges 16 4-8 8 2-4 6 6-7 16 Apr. 22, 1866 Mine of Forchier 19 8-2 9 10-1 "' 17 18 19 20 July 31, 1865 Mar. 1866 Mar. 25, 1866 Colliery of Crachet and Picquery Ditto . .. 22 11-5 22 11-5 22 11-5 22 11-5 9 10-1 9 10-1 9 10-1 9 10-1 5 6-9 5 6-9 5 6-9 5 6-9 Ditto Grand Buisson 21 22 23 24 25 Sept. 11, 1870 1866 Oct. 24, 1869 May 17, 1869 June 21, 1869 Grand Mambourg 22 11-5 22 11-5 29 6'2 29 6-2 29 6-2 9 10-1 9 10-1 9 10-1 9 10-1 9 10-1 8 2-4 5 6-9 6 6-7 6 6-7 6 6-7 RieuduCoeur Louviere . . . . . Grand Buisson 26 Mar. 25, 1877 Crachet and Picquery 39 4-313 1-4 1 8 2-4 WORKSHOP 27 .. Uncovered Fan of M. Tournaire 2 9-5 1 6-9 28 July 22, 1855 Ventilator given to Exhibition by M. de Lacolonge. 3 3-0 10-2 6-0 29 Ventilator made for charcoal furnace by M. Rittenger. 5 3-0 1 2-2 3-5 CENTRIFUGAL VENTILATING MACHINES. 69 No. III. continued. Publications. Authors. Manometric Yield. Observations. Min. Max. EVASEE CHIMNEY (GUIBAL TYPE). Notes Cabany 0-418 0-460 Watt indicator. Ditto Ditto 0-510 0-640 Ditto. Bulletin of Mineral Aguillon, 0-250 0-494 Ditto. The small yield was Industry, Vol. VII. Fumat, and obtained on a thin mine. Murgue. Ventilation of Mines, Stoesser and 0-413 0-455 Ditto dittot Devillez. Devillez. Ditto Gille and 0-380 0-610 Ditto, same far as No. 6, com- Fraueau. plete. Ditto .. 0-307 0-749 Ditto. Experiments made when mine much altered. Ditto Stoesser and 0-440 0-501 Ditto. Devillez. Ditto .. 0-426 0-725 Ditto, same fan as No 12, chimney complete. Ditto De Poitier 0-426 0-534 Ditto. This fan is of great width. Unpublished C. Brice 0-230 0-410 Ditto. Ventilation by Devillez Brunin and 0-452 0-580 Ditto. others. Ditto Roger and 0-279 0-513 Ditto. Halley. Ditto 0-382 0-382 Ditto. Revue Universelle, Hubert, 0-538 0-555 Ditto. July 1877. Devillez. BLOWING FANS. AnnalesdesMines,1860 Tournaire 0-240 0-500 Prony brake. The "Genie Industrie!" Experiments 0-132 0-646 Ditto. at Conser- vatoire des Arts et Metiers. Ventilation, by Ritten- ger, 1858. Rittenger 0-110 0-230 Ditto. Equivalent orifice very small and so yield and effect is poor. 70 THE THEORIES AND PRACTICE OF under inconvenient working conditions and often those unfavourable to the yield. I think that we may accept the number 0*500 as representing with sufficient exact- ness the average yield of this kind of machine under the conditions in which they generally work. It is the result of experiments made with Watt's indicator, the only dynamo- meter possible with direct-acting machines. If we could have measured the motive power on the shaft itself with the aid of dynamometers, or even by the torsion on the shaft as has been proposed by M. Him, we should certainly have obtained a higher yield. 6. CONCLUSIONS. I will now give a resume, in a few lines, of the theoretical views developed in the preceding paragraphs. In theory every deprimogen ventilator turning under the action of a motor, gives a certain depression depending entirely on the tangential speed, and consequently independent of the volume of air which it yields. This depression has for its value H - " 2 - H ~g In practice two causes occur to prevent the effective depression yielding this ideal value. First, imperfections of different kinds, independent of yield, oblige us to apply to the preceding expression a coefficient of reduction K, which we have named the manometrical yield. Second, the frictions and losses of the load of air traversing the machine, losses proportional to the square of the yield, and expressed by the area of the orifice of passage o. CENTRIFUGAL VENTILATING MACHINES. 71 From these two enfeebling^ causes, the value for the effective depression becomes (+5) From the knowledge of the effective depression and the equivalent orifice of the mine, there is deduced by the appli- cation of a formula for the flow in a thin medium, the volume of air yielded V = ' 65 Finally the product of volume by the theoretical depres- sion which virtually subsists, and gives to the motor the same load as if it had been manifest, gives, in taking account of passive resistances, the value of the motive power T - V H -4- T -*-m - LJ -o \ *-$ In the first part of this study, published in 1872, 1 stated in the following terms the problem of mine ventilation : To make a given quantity of air traverse a given mine. Then, having proposed to represent mines by their equiva- lent orifices, I thus modified this statement : To make a given volume of air circulate through an orifice in a thin medium. I cannot pretend that it is always in these terms that the problem presents itself to those studying it; but it is at least the most general one, and it cannot give any difficulty in the treatment of it under different forms. 72 THE THEOEIES AND PRACTICE OF Let a volume V be made to pass through an orifice a. Let h be the necessary depression to cause this circulation, a depression which will be immediately given by the formula of the flow through a thin medium The engineer should then decide upon the type of machine that he intends to adopt. Theory and experience show that the best deprimogen ventilator is the ventilator with centrifugal force, in which the air expelled by the vanes is received in evasee channels, like those of the Guibal ventilator. Let us admit, then, that choice is made of the Guibal ventilator. For comparison with existing machines, we observe that the manometrical yield in these ventilators may be estimated at 750. As to the orifice of passage, it is more difficult to decide, this element depending especially on the width, on the eccentricity, and on the ouie. I have only given three examples of the orifice of passage, those of the ventilators of Besseges, Creal, and Lalle ; they may assist in suggesting a provisional hypothesis, and then, introducing these two data K and o in the formula for effective depression, K'+S) we have an equation from which it would be easy to deduce the value of the tangential speed u. This is the exact method arising rationally from our theory ; there is another, more approximative but more simple, and in fact sufficient for the application ; it is based on the knowledge of the approximate manometrical yield. This yield, according to our first table, is on an average, for CENTRIFUGAL VENTILATING MACHINES. 73 Guibal ventilators, 650. This figure increases a little for thin seams and diminishes for thick ones. Dividing the effective depression by this coefficient, always, it is true, somewhat arbitrary, we obtain the theoretical depression whence we deduce easily the value of the tangential speed u. This tangential speed is a most important factor in the construction of deprimogen ventilators. We may see this either in a small ventilator turning with great speed, or in a large machine turning slowly. On this point the con- structor is altogether free, and may be guided by con- siderations of the place for which it is required, of economy, and of mechanical simplicity. The form to be given to the vanes has been described before. They should present to the circumference of the ouie an inclination following the resultant of their move- ment of rotation and of the movement of the air pene- trating their spaces. From this they should incline by a gentle curve, and terminate by a part directly following the radius. As to their number, it seems to me that it is an advantage to make them numerous; they guide the air better and shake less. The only objection is that by the thickness being repeated they rather reduce the orifice of The motive power to be applied to the machine so defined will be given by the formula whence it suffices to make an hypothesis on the value of the passive resistances as far as it is known ; but that is all the sim- plification possible. We have seen that the average value of 74 THE THEORIES AND PRACTICE OF the mechanical yield observed at the indicator with Guibal ventilators is 500 ; it is sufficient, then, if we have the elements of useful work YA, to double them in order to obtain with a sufficient approximation for practice the work to be applied to the piston of the motive power. There remain to be determined the diameter of the ouie, the width and the eccentricity, &c., but these elements result from considerations altogether different from those which I have enumerated, and I will return to this study for the fourth occasion, and I hope the last one, if circumstances permit me to establish the theoretical and practical conditions which exist in the best ventilators. BESSEGES, January 17, 1880. CENTRIFUGAL VENTILATING MACHINES. 75 ADDITIONAL NOTES. NOTE A. The Theory of Bernoulli. This theory, which forms the base of hydraulics, may be thus expressed: When a fluid vein where there is an established condition flows in any given form, if we make abstraction of the frictions which occur on the sides, at each point, the generative height of the speed, the pressure mea- sured in column of fluid, and the height above an arbitrary horizontal plane, form a total constant V 2 - f- H -f- Z = constant. ^9 In the questions relative to ventilation the fluid veins in an atmosphere of the same character and the same density as themselves are not affected by the action of their own weight. Consequently a vein moving primitively in the horizontal plane may be inclined in any direction whatever without being affected by the vertical displacement of its molecules. This remark enables us to eliminate the term Z of the preceding expression, and to reduce it to the simple binomial V* (- H = constant. ^9 Thus in the vein of air the generative height of the speed and the pressure mutually compensate each other, the one increasing as the other weakens. Let us consider two points, more or less distant from one another, in the same vein of air, their pressures and speeds 76 THE THEOBIES AND PRACTICE OF being H and V for the first point, H' and V for the second. We may then write or rather, by calling h the increase H' H of the pressure, an expression which may be thus translated : When the speed of a vein of air gradually diminishes from one point to another, the increase of the pressure is equal to the diminution of the generative head of the speed. It is this statement which I assume to be present to the mind of the reader whenever in the course of this study I made reference to the theory of Bernoulli i. NOTE B. Of the law of Proportionality between the Volume yielded and the speed of Rotations, and between Depression and the Square of this Speed. All the published experiments, and all those which I have made myself on the ventilator of the mine of Creal, agree as to the evidence of this double proportionality. I will record two of the latter experiments taken promiscuously. The first, on the 26th August, 1876, includes three observa- tions of the volume yielded at three different speeds of the ventilator. Measurements were made with the aid of the anemometer of Combes. Twenty-three observations of speed made in twenty-three spaces being regularly divided over the section of measurement have allowed us to establish an average speed with a very satisfactory exactness. The numbers of the last column indicate the proportion of the yield CENTKIFUGAL VENTILATING MACHINES. 77 to the speed of rotation, or, if we prefer, the number of cubic feet yielded per revolution of the machine. Revolu- Volume Proportion No. tions per Minute. per Second. of Yield to Speed. 1 40-8 315-4 7'73 2 49-2 386-9 7-86 3 .58-3 454-6 7-79 The regularity of the final proportion leaves no doubt, especially if we take account of the difficulty in every particular in this kind of observation. This proportional increase will evidently continue as far as it is possible to push the speed of the ventilator. Still, it is difficult to understand the opinion which we sometimes hear expressed that beyond a certain speed the yield ceases to increase, or rather only increases very slowly. It cannot be based upon any experiments which are sufficiently exact. The volume yielded per revolution of the machine remains constant so long as the resistance of the mine itself does not vary ; but it is clearly connected with this resistance, so that every variation in the value of the equivalent orifice shows itself by a corresponding variation almost proportion- ally to the yield per revolution. This observation suffices to show how irrational it is to seek to establish, as some writers have done, a more or less constant relation between the volume yielded and the volume generated by the rotation of the vanes. This kind of relation has no serious signi- ficance except for volumogen ventilators. The second series of observations which I produce here was made on the 14th January, 1872 ; the depressions alone have been observed with a somewhat doubtful approxima- tion to the extent of ^^ of an inch. The second column gives the squares of the speeds of rotation, and the last the proportion of the depressions to those of the square of the 78 THE THEORIES AND PRACTICE OF speed, a proportion of which it is necessary to verify the regularity : No. Revolu- tions per Minute. Square of Number of Revolutions. Water Gauge. (Inches.) Proportion of Depression to the Square of 1 33-8 1142-44 0-323 000282 2 39-8 1584-04 0-444 000280 3 49-0 2401-00 0-670 000279 4 56-8 3226-24 0-893 000276 5 64-0 4096-00 1-134 000276 Here, again, the regularity of the final proportion proves itself in a sufficiently clear manner, having regard to the difficulty of measuring the depression with certainty in the midst of incessant oscillations. We observe that the numerical value of this proportion falls in a regular slowly decreasing progression. There is here a certain indication of a natural action which was easily accounted for at the time the experiment was made. The chimney of the ventilator gives rise to a certain amount of aspiration, which is added to the effect produced by the vanes affecting relatively more the cases of weak depressions. When the natural movement is lively it affects very strongly the double proportionality which we seek to establish by experimental verification. To see it most distinctly in the case of the depression the best plan is to make a drawing of it, with the squares of the speeds for abscissae and the observed depressions as ordinates. The points so obtained arrange themselves in a straight line, which, instead of coinciding with the origin itself, passes above or below it, at a distance which gives the exact measure of the action which is so troublesome. In the case of the volume where this action has an influence still greater we place in the abscissae not the speed itself, but its square, and in the ordinates the square of the yield. In effect, if h represents the depression due to the natural action, and h that due to the ventilator alone, CENTRIFUGAL VENTILATING MACHINES. 79 the volume yielded, given by the formula of escape in the thin medium, would have for expression V = 0-65 a J2g(h A ), and by raising it to the square V 2 = (F65 2 a* 2 g (h h }. Remarking that h is proportional to the square of the speed, and that the product 65 a 2 2 g is constant, I may thus transform this equation If for the present we take d. SPONS' HOUSEHOLD MANUAL: A Treasury of Domestic Eeceipts and Guide for Home Management. PRINCIPAL CONTENTS. Hints for selecting 1 a good House, pointing out the essential requirements for a good house as to the Site, Soil, Trees, Aspect, Construction, and General Arrangement ; with instructions for Reducing Echoes, Waterproofing Damp Walls, Curing Damp Cellars. Sanitation- What should constitute a good Sanitary Arrangement : Examples (with illustrations) of Well- and Ill-drained Houses ; How to Test Drains ; Ventilating Pipes, etc. "Water Supply. Care of Cisterns; Sources of Supply; Pipes; Pumps; Purification and Filtration of Water. Ventilation and "Warming 1 . 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Useful Propositions and Rules. Breweries and Mailings : their Arrangement, Con- struction, Machinery, and Plant. By G. SCAMELL, F.R.I.B.A. Second edition, revised, enlarged, and partly rewritten. By F. COLYER, M.I.C.E., M.LM.E. With 20 plates, 8vo, cloth, i8j. A Practical Treatise on the Construction of Hori- zontal and Vertical Watcrwheels, specially designed for the use of opera- tive mechanics. By WILLIAM CULLEN, Millwright and Engineer. With II plates. Second edition, revised and enlarged, small 4to, cloth, \2s. 6d. A Practical Treatise on Mill-gearing, Wheels, Shafts, Riggers, etc. ; for the use of Engineers, edition, with 1 1 plates. Crown 8vo, cloth, "js Riggers, etc.', for the use of Engineers. By THOMAS Box. Third . 6d. Mining 1 Machinery: a Descriptive Treatise on the Machinery, Tools, and other Appliances used in Mining. By G. G. ANDRE, F.G.S., Assoc. Inst. C.E., Mem. of the Society of Engineers. Royal 4to, uniform with the Author's Treatise on Coal Mining, con- taining 182 plates, accurately drawn to scale, with descriptive text, in 2 vols., cloth, 3/. 12.5. CONTENTS : Machinery for Prospecting, Excavating, Hauling, and Hoisting Ventilation Pumping Treatment of Mineral Products, including Gold and Silver, Copper, Tin, and Lead, Iron Coal, Sulphur, China Clay, Brick Earth, etc. Tables for Setting out Curves for Railways, Canals, Roads, etc., varying from a radius of five chains to three miles. By A. KENNEDY and R. W. HACKWOOD. Illustrated, 32mo, cloth, is. 6J. PUBLISHED BY E. & F. N. SPON. n The Science and Art of the Manufacture of Portland Cement, with observations on some of its constructive applications. With 66 illustrations. By HENRY REID, C.E., Author of 'A Practical Treatise on Concrete,' etc., etc. 8vo, cloth, iSs. The Draughtsman s Handbook of Plan and Map Drawing; including instructions for the preparation of Engineering, Architectural, and Mechanical Drawings. With numerous illustrations in the text, and 33 plates (15 printed in colours}. By G. G. ANDRK, F.G.S., Assoc. Inst. C.E. 4to, cloth, 9*. CONTENTS : The Drawing Office and its Furnishings Geometrical Problems Lines, Dots, and their Combinations Colours, Shading, Lettering, Bordering, and North Points Scales Plotting Civil Engineers' and Surveyors' Plans Map Drawing Mechanical and Architectural Drawing Copying and Reducing Trigonometrical Formulae, etc., etc. T he B oiler-maker s andiron Ship-bitilder s Companion, comprising a series of original and carefully calculated tables, of the utmost utility to persons interested in the iron trades. By JAMES FODEN, author of ' Mechanical Tables,' etc. Second edition revised, with illustra- tions^ crown 8vo, cloth, 5-r. Rock Blasting: a Practical Treatise on the means employed in Blasting Rocks for Industrial Purposes. By G. G. ANDRE, F.G.S., Assoc. Inst. C.E. With 56 illustrations and 12 plates, 8vo, cloth, Painting" and Painters Manual: a Book of Facts for Painters and those who Use or Deal in Paint Materials. By C. L. CONDIT and J. SCHELLER. Illustrated, 8vo, cloth, IQJ. 6d. A Treatise on Ropemaking as practised in public and private Rope-yards, with a Description of the Manufacture, Rules, Tabler. of Weights, etc., adapted to the Trade, Shipping, Mining, Railways, Builders, etc. By R. CHAPMAN, formerly foreman to Messrs. Huddart and Co., Limehouse, and late Master Ropemaker to H.M. Dockyard, Deptford. Second edition, I2mo, cloth, 3-r. Laxtons Builder and Contractors Tables ; for the use of Engineers, Architects, Surveyors, Builders, Land Agents, and others. Bricklayer, containing 22 tables, with nearly 30,000 calculations. 4to, cloth, 5-r. Laxtons Builders and Contractors Tables. Ex- cavator, Earth, Land, Water, and Ga's, containing 53 tables, with nearly 24,000 calculations. 4to, cloth, 5*. 12 CATALOGUE OF SCIENTIFIC BOOKS Sanitary Engineering: a Guide to the Construction of Works of Sewerage and House Drainage, with Tables for facilitating the calculations of the Engineer. By BALDWIN LATHAM, C.E., M. Inst. C.E., F.G.S., F.M.S., Past-President of the Society of Engineers. Second edition, with numerous plates and woodcuts, Svo, cloth, I/. ioj. Screw Cutting Tables for Engineers and Machinists, giving the values of the different trains of Wheels required to produce Screws of any pitch, calculated by Lord Lindsay, M.P., F.R.S., F.R.A.S., etc. Cloth, oblong, 2s. Screw Cutting Tables, for the use of Mechanical Engineers, showing the proper arrangement of Wheels for cutting the Threads of Screws of any required pitch, with a Table for making the Universal Gas-pipe Threads and Taps. By W. A. MARTIN, Engineer. Second edition, oblong, cloth, u., or sewed, 6d. A Treatise on a Practical Method of Designing Slide- Valve Gears by Simple Geometrical Construction, based upon the principles enunciated in Euclid's Elements, and comprising the various forms of Plain Slide- Valve and Expansion Gearing ; together with Stephenson's, Gooch's, and Allan's Link-Motions, as applied either to reversing or to variable expansion combinations. By EDWARD J. COWLING WELCH, Memb. Inst. Mechanical Engineers. Crown Svo, cloth, 6.r. Cleaning and Scouring : a Manual for Dyers, Laun- dresses, and for Domestic Use. By S. CHRISTOPHER. i8mo, sewed, 6d. A Glossary of Terms itsed in Coal Mining. By WILLIAM STUKELEY GRESLEY, Assoc. Mem. Inst. C.E., F.G.S., Member of the North of England Institute of Mining Engineers. Illustrated with numerous woodcuts and diagrams, crown Svo, cloth, 5^. A Pocket-Book for Boiler Makers and Steam Users, comprising a variety of useful information for Employer and Workman, Government Inspectors, Board of Trade Surveyors, Engineers in charge of Works and Slips, Foremen of Manufactories, and the general Steam- using Public. By MAURICE JOHN SEXTON. Second edition, royal 32mo, roan, gilt edges, 5-r. Electrolysis: a Practical Treatise on Nickeling, Coppering, Gilding, Silvering, the Refining of Metals, and the treatment of Ores by means of Electricity. By HIPPOLYTE FONTAINE, translated from the French by J. A. BERLY, C.E., Assoc. S.T.E, With engravings. SvOj cloth, Qj-. PUBLISHED BY E. & F. N. SPON. 13 Barlow s Tables of Squares, Cubes, Square Roots, Cube Roots , Reciprocals of all Integer Numbers np to 10,000. Post 8vo, cloth, 6s. A Practical Treatise on the Steam Engine, con- taining Plans and Arrangements of Details for Fixed Steam Engines, with Essays on the Principles involved in Design and Construction. By ARTHUR RIGG, Engineer, Member of the Society of Engineers and of the Royal Institution of Great Britain. Demy 410, copiously illustrated with woodcuts and 96 plates, in one Volume, half-bound morocco, 2/. 2s. ; or cheaper edition, cloth, 2$s. _This work is not, in any sense, an elementary treatise, or history of the steam engine, but is intended to describe examples of Fixed Steam Engines without entering into the wide domain of locomotive or marine practice. To this end illustrations will be given of the most recent arrangements of Horizontal, Vertical, Beam, Pumping, Winding, Portable, Semi- portable, Corliss, Allen, Compound, and other similar Engines, by the most eminent Firms in Great Britain and America. The laws relating to the action and precautions to be observed in the construction of the various details, such as Cylinders, Pistons, Piston-rods, Connecting- rods, Cross-heads, Motion-blocks, Eccentrics, Simple, Expansion, Balanced, and Equilibrium Slide-valves, and Valve-gearing will be minutely dealt with. In this connection will be found articles upon the Velocity of Reciprocating Parts and the Mode of Applying the Indicator, Heat and Expansion of Steam Governors, and the like. It is the writer's desire to draw illustrations from every possible source, and give only those rules that present practice deems correct. A Practical Treatise on the Science of Land and Engineering Surveying, Levelling, Estimating Quantities ; etc., with a general description of the several Instruments required for Surveying, Levelling, Plotting, etc. By H. S. MERRETT. Fourth edition, revised by G. W. USILL, Assoc. Mem. Inst. C.E. 41 plates, with illustrations and tables, royal 8vo, cloth, 12s. 6d. PRINCIPAL CONTENTS : Part i. Introduction and the Principles of Geometry. Part 2. Land Surveying; com- prising General Observations The Chain Offsets Surveying by the Chain only Surveying Hilly Ground To Survey an Estate or Parish by the Chain only Surveying with the Theodolite Mining and Town Surveying Railroad Surveying Mapping Division and Laying out of Land Observations on Enclosures Plane Trigonometry. Part 3. Levelling Simple and Compound Levelling The Level Book Parliamentary Plan and Section Levelling with a Theodolite Gradients Wooden Curves To Lay out a Railway Curve- Setting out Widths. Part 4. Calculating Quantities generally for Estimates Cuttings and Embankments Tunnels Brickwork Ironwork Timber Measuring. Part 5. Description and Use of Instruments in Surveying and Plotting The Improved Dumpy Level Troughton's Level The Prismatic Compass Proportional Compass Box Sextant Vernier Panta- graph Merrett's Improved Quadrant Improved Computation Scale The Diagonal Scale Straight Edge and Sector. Part 6. Logarithms of Numbers Logarithmic Sines and Co-Sines, Tangents and Co-Tangents Natural Sines and Co-Sines Tables for Earthwork, for Setting out Curves, and for various Calculations, etc., etc., etc. Health and Comfort in House Building, or Ventila- tion with Warm Air by Self-Acting Stiction Po^uer, with Review of the mode of Calculating the Draught in Hot- Air Flues, and with some actual Experiments. By J. DRYSDALE, M.D., and J. W. HAYWARD, M.D. Second edition, with Supplement, with plates^ demy 8vo, cloth, "js. 6d. CATALOGUE OF SCIENTIFIC BOOKS. The Assayers Manual: an Abridged Treatise on the Docimastic Examination of Ores and Furnace and other Artificial Products. By BRUNO KERL. Translated by W. T. BRANNT. With 65 illustrations, 8vo, cloth, 12s. 6d. Electricity: its Theory, Sources, and Applications. By J. T. SPRAGUE, M.S.T.E. Second edition, revised and enlarged, with numerous illustrations, crown 8vo, cloth, 15^. The Practice of Hand Turning in Wood, Ivory, Shell, etc., with Instructions for Turning such Work in Metal as may be required in the Practice of Turning in Wood, Ivory, etc. ; also an Appendix on Ornamental Turning. (A book for beginners.) By FRANCIS CAMPIN. Third edition, with wood engravings, crown 8vo, cloth, 6s. CONTENTS : On Lathes Turning Tools Turning Wood Drilling Screw Cutting Miscellaneous Apparatus and Processes Turning Particular Forms Staining Polishing Spinning Metals Materials Ornamental Turning, etc. Treatise on Watchwork, Past and Present. By the Rev. H. L. NELTHROPP, M.A., F.S.A. With 32 illustrations, crown 8vo, cloth, 6s. 6d. CONTENTS : Definitions of \Vords and Terms used in Watchwork Tools Time Historical Sum- mary On Calculations of the Numbers for Wheels and Pinions; their Proportional Sizes, Trains, etc. Of Dial Wheels, or Motion Work- Length of Time of Going without Winding up The Verge The Horizontal The Duplex The Lever The Chronometer Repeating Watches Keyless Watches The Pendulum, or Spiral Spring Compensation Jewelling of Pivot Holes Clerkenwell Fallacies of the Trade Incapacity of Workmen How to Choose and Use a Watch, etc. Algebra Self-Taught. By W. P. HIGGS, M.A., D.Sc., LL.D., Assoc. Inst C.E., Author of ' A Handbook of the Differ- ential Calculus,' etc. Second edition, crown 8vo, cloth, 2s. 6d. CONTENTS : Symbols and the Signs of Operation The Equation and the Unknown Quantity Positive and Negative Quantities Multiplication Involution Exponents Negative Expo- nents Roots, and the Use of Exponents as Logarithms Logarithms Tables of Logarithms and Proportionate Parts Transformation of System of Logarithms Common Uses of Common Logarithms Compound Multiplication and the Binomial Theorem Division, Fractions, and Ratio Continued Proportion The Series and the Summation of the Series Limit of Series Square and Cube Roots Equations List of Formulae, etc. Spons Dictionary of Engineering, Civil, Mechanical, Military, and Naval j with technical terms in French, German, Italian, and Spanish, 3100 pp., and nearly 8000 engravings, in super-royal 8vo, in 8 divisions, 5/. &s. Complete in 3 vols., cloth, 5/. $s. Bound in a superior manner, half-morocco, top edge gilt, 3 voh., 61. 12s. PUBLISHED BY E. & F. N. SPON. 15 Notes in Mechanical Engineering. Compiled prin- cipally for the use of the Students attending the Classes on this subject at the City of London College. By HENRY ADAMS, Mem. Inst. M.E., Mem. Inst. C.E., Mem. Soc. of Engineers. Crown 8vo, cloth, 2r. 6d. Canoe and Boat Building: a complete Manual for Amateurs, containing plain and comprehensive directions for the con- struction of Canoes, Rowing and Sailing Boats, and Hunting Craft. By W. P. STEPHENS. With numerous illustrations and 24 plates of Working Drawiugs. Crown 8vo, cloth, 'js. 6d. Proceedings of the National Conference of Electricians^ Philadelphia, October 8th to I3th, 1884. i8mo, cloth, 3*. Dynamo - Electricity, its Generation, Application, Transmission, Storage, and Measurement. By G. B. PRESCOTT. With 545 illustrations. 8vo, cloth, I/, u. Domestic Electricity for Amateurs. Translated from the French of E. HOSPITALIER, Editor of " L'Electricien," by C. J. WHARTON, Assoc. Soc. Tel. Eng. Numerous illustrations. Demy 8vo, cloth, gs. CONTENTS: i. Production of the Electric Current 2. Electric Bells 3. Automatic Alarms 4. Domestic Telephones 5. Electric Clocks 6. Electric Lighters 7. Domestic Electric Lighting 8. Domestic Application of the Electric Light 9. Electric Motors 10. Electrical Locomo- tion ii. Electrotyping, Plating, and Gilding 12. Electric Recreations 13. Various appli- cations Workshop of the Electrician. Wrinkles in Electric Lighting. By VINCENT STEPHEN. With illustrations. i8mo, cloth, 2s. 6d. CONTENTS: i. The Electric Current and its production by Chemical means i. Production of Electric Currents by Mechanical means 3. Dynamo-Electric Machines 4. Electric Lamps 5. Lead 6. Ship Lighting. The Practical Flax Spinner ; being a Description of the Growth, Manipulation, and Spinning of Flax and Tow. By LESLIE C. MARSHALL, of Belfast. With illustrations. 8vo, cloth, I5J-. Foundations and Foundation Walls for all classes of Buildings, Pile Driving, Building Stones and Bricks, Pier and Wall construction, Mortars, Limes, Cements, Concretes, Stuccos, &c. 64 illus- trations. By G. T. POWELL and F. BAUMAN. 8vo, cloth, IQJ-. 6