T N 
 
 UC-NRLF 
 
 /?* 
 
 
REESE LIBRARY 
 
 OF THE 
 
 UNIVERSITY OF CALIFORNIA 
 
 Received C^f CClJ , i8gf 
 
 Accessions No.^&' 2-2- Shelf No.. 
 
A PRACTICAL TREATISE 
 
 GASES MET WITH IN COAL MINES 
 
 GENERAL PRINCIPLES OF VENTIL/TION. 
 
 BY THE LATE 
 
 J. J. ATKINSON, 
 t 
 
 GOVERNMENT INSPECTOR or MINES FOR THE COUNTY OF DURHAM. 
 
 NEWCASTLE-TJPON-TYNE : 
 ANDREW REID, PRINTING COURT BUILDINGS, AKENSIDE TTTT.T, 
 
 LONDON: 
 LONGMANS, GREEN, LONGMANS, & CO. 
 

 NEWCASTLE-UPON-TYNE : 
 ANDREW REID, PRINTING COURT BXTILDINGS, AKENSIDE HILL. 
 
PREFACE. 
 
 THE Manchester Geological Society, before whom 
 this valuable Treatise was read in the session of 
 1862, having kindly permitted its reprint, to assist 
 the fund now being formed for the family of the 
 late J. J. Atkinson, it is now offered to all who are 
 interested in these, the most important questions of 
 mining science, as the most thorough essay on the 
 subjects of which it treats. 
 
 Starting with elementary principles and defini- 
 tions, and with the aid of the most simple illustra- 
 tions, the author has worked out the laws which 
 govern the ventilation of our mines in a manner so 
 clear and so convincing as to bring the subjects, 
 hitherto deemed so difficult, within the easy compre- 
 hension of every educated miner. It is well known 
 that the late J. J. Atkinson was an authority upon 
 the most complicated questions of ventilation, the 
 larger and more extended knowledge of this subject 
 being due principally to his teaching, and, therefore, 
 no one was better able to undertake such a work. 
 
IV 
 
 In commenting on the Treatise, the President of 
 the Manchester Geological Society remarked: 
 
 " I think those of you who were present at the last 
 meeting will remember that Mr. Atkinson, in the opening 
 of his first paper on this subject, said, that it might be 
 useful for young colliery viewers, underlookers, and work- 
 people who might wish to raise themselves ; and there is 
 no doubt it will be useful to those ; but I think, if his 
 modesty had not been so great, he might have said it would 
 form the most useful book of reference that we have as yet 
 published on the subject of the ventilation of mines. I 
 know of no elementary treatise in which the subjects are so 
 well brought forward, and so many tables given, which will 
 be valuable not only to the beginner but to the viewer as 
 a book of reference." 
 
 No further recommendation is needed of the 
 merits of the treatise, but it may add to the success 
 of the generous object which the author had in 
 writing it, if it is known that of his many works 
 for the advancement of the art of mining, this is 
 the only one which can be made available for the 
 benefit of his widow and family, from whom he has 
 so suddenly been removed. The proceeds will go 
 to the augmentation of the " Atkinson Memorial 
 Fund." 
 
ON THE 
 
 GASES MET WITH IN COAL MINES, 
 
 AUD THE 
 
 GENERAL PRINCIPLES OF VENTILATION. 
 
 THE following remarks were written in the hope that 
 some or other of them might prove of service in conveying 
 to the merely practical miner a general knowledge of 
 the laws and principles of ventilation, as applied to mines, 
 and of the nature and properties, chemical and physical, 
 of our atmosphere, as well as those of some of the gases 
 most frequently encountered in coal mines. They were 
 not intended to have been communicated to this or any 
 similar institution, or they would, in all probability, not 
 only have been put into somewhat different language, 
 but would also have placed some of the matters to which 
 they refer in a more purely scientific point of view. But, 
 after all, such an alteration would, perhaps, have rendered 
 them less useful than it is hoped they may prove to the 
 particular class of persons for whom they were written, 
 such as underviewers, overmen, deputy-overmen, and even 
 workmen who may wish to fit themselves for assuming any 
 of these offices; and, at the request of my colleague, your 
 present President, I venture to submit them to your notice. 
 A variety of gases is given off by the coal and other 
 minerals met with in coal mines; a farther supply of gases 
 
arises from the breathing of men and animals, and from 
 the burning of candles and lamps, as well as from the 
 explosion of the powder used for blasting the coal and 
 stone in the mines. The whole of these gases are capable 
 of causing the death of men and animals breathing them 
 in their pure and undiluted state, and some of them re- 
 quire to be mixed with many times their own volume of 
 air before the mixture they form with it can be breathed, 
 for any great length of time, with safety. 
 
 Some of the gases given off in coal mines, when mixed 
 with certain proportions of air, form violently explosive 
 mixtures. Such a mixture of air and gas, on being ignited 
 by a naked candle or other flame, suddenly explodes and 
 becomes one mass of living flame, scorching and burn- 
 ing everything that may happen to be in contact with 
 it. Such an explosion, in general, also creates a com- 
 plete hurricane, or tornado, of immense force and violence, 
 tearing and driving all before it knocking down the 
 masonry erected for the guidance of the ventilation, as 
 well as the props and timber erected to support the roof 
 of the mine, which falls in great masses, causing bodily 
 injury or death to those it may fall upon, and often 
 enclosing and imprisoning those who, being unhurt by 
 its fall, are left stunned by the concussion, more or less 
 scorched by the flames, and, without lights, shut up 
 to breathe the deleterious atmosphere produced by the 
 explosion. The flames of such an explosion being extin- 
 guished, and its violence exhausted, there remains an atmos- 
 phere so hot, and so charged with noxious gases and steam, 
 as to cause the death of all who are left alive to inhale or 
 breathe it. This resulting atmosphere is generally termed 
 after-damp. 
 
3 
 
 The grand object of the ventilation of mines is to cause 
 such a current of air constantly to circulate through them 
 as shall, by mixing with and diluting the gases, render 
 them harmless, and, in that state, carry them off as quickly 
 as they are produced in the mines. It is here proposed, 
 in the first instance, to remark upon the chemical compo- 
 sition of the air we breathe; then upon that of a few of the 
 most important gases met with in coal mines ; and after- 
 wards to notice some of the leading principles of ventilation, 
 by taking advantage of which we get rid of the gases as 
 fast as they are given off in mines. 
 
 ATMOSPHERIC AIR. 
 
 Air is, almost entirely, a mixture of two gases, oxygen 
 and nitrogen; carbonic acid is also present in limited but 
 variable proportions, forming on an average about 1 part 
 to 2,500 parts of our atmosphere. Besides oxygen, nitrogen, 
 and a trace of carbonic acid gas in the atmosphere, there is 
 always more or less of watery vapour diffused through the 
 gases of which it is composed; but this vapour is variable 
 in amount, is not considered as forming a constituent part 
 of the atmosphere, and is therefore not embraced in state- 
 ments as to the chemical composition of air; yet its 
 effects are of the highest importance, both in the general 
 economy of nature, and also in considerations relative 
 to the ventilation of mines. Dry air is chemically com- 
 posed of 
 
 By Weight. By Volume. 
 
 Nitrogen gas ... 77 per cent. ... 79 per cent. 
 Oxygen gas ... J23 ... J21 
 
 100 100 
 
 A cubic foot of 'air at the temperature of melting ice (32), 
 
and under pressure of 14' 7 Ibs. per square inch, or 2116*8 
 Ibs. per square foot, weighs 0*080728 Ibs.; so that under 
 the same conditions 1,000 cubic feet weigh 80*728 Ibs. 
 avoirdupois. 
 
 NITROGEN GAS. 
 
 Nitrogen gas is rather lighter than air, taken in equal 
 volumes, at the same temperature, and under the same 
 pressure. The specific gravity of air being taken as 1,000, 
 that of nitrogen gas is only 971'37, so that the weight of 
 1,000 cubic feet of air being 80' 728 Ibs.,' that of 1,000 
 cubic feet of nitrogen is only 78*416 Ibs. at the temperature 
 (32) of melting ice, and under the pressure of the atmos- 
 phere, taken at 14*7 Ibs. per square inch, or 2116*8 Ibs. 
 per square foot. A cubic foot of nitrogen, under the same 
 conditions of temperature and pressure, weighs 0*0784167 
 Ibs., and a cubic foot of air 0*080728 Ibs., as before stated. 
 
 Nitrogen gas has neither colour, taste, nor smell, and so 
 far it is like air itself. It will not support life, but causes 
 death when breathed. It will not support combustion, 
 but extinguishes lights. This gas has very little chemical 
 affinity or attraction for other bodies ; its chemical pro- 
 perties are rather those of indifference than of activity ; 
 its position amongst gases, in general, being almost like 
 that of water amongst liquids, as it serves to render their 
 properties less active. It dilutes the oxygen of the atmos- 
 phere, which could not long be breathed without being 
 diluted with nitrogen. Nitrogen is, however, probably the 
 best part of manures for land ; and it is a component part 
 of nitrous oxide or laughing gas, of ammonia, and of 
 nitric acid or aquafortis, as well as of many other com- 
 pounds. 
 
/T 
 
 I. 0* THE r 
 
 ft UNIVERSITY 
 5 
 
 OXYGEN GAS. 
 
 Oxygen gas, as has been stated, forms about 21 parts 
 by volume, or 23 parts by weight, out of every 100 parts 
 of air, being rather more than one-fifth part. The specific 
 gravity of air being taken as 1,000, that of oxygen gas 
 is 1105-63; 1,000 cubic feet of air at 32, and under a 
 pressure of 14*7 Ibs. per square inch, weigh 80*728 Ibs.; 
 1,000 cubic feet of oxygen gas, under the same conditions, 
 weigh 89*255 Ibs.; so that this gas is rather heavier than 
 an equal volume of air. Oxygen gas has neither colour, 
 taste, nor sinell. This gas, in a free and uncombined state, 
 is essential to life; we must breathe it in this state or die; 
 in its undiluted state it is not fit to breathe beyond a very 
 short time. In our atmosphere it is fitted to sustain life 
 by dilution or mixture with nitrogen gas. Chemical com- 
 pounds in the gaseous form may contain large proportions 
 of oxygen and yet be unfit for respiration or breathing ; 
 to be suited for this purpose, the oxygen must be free and 
 uncombined, and at the same time diluted. 
 
 Oxygen is the most abundant substance in nature, and 
 constitutes at least one-third of the solid mass of the earth 
 23 per cent, of air, and 89 per cent, of water. Oxygen 
 has strong affinities, and combines with all known substances 
 excepting fluorine. It forms, with other substances, no 
 less than 136 inorganic compounds, and it would be diffi- 
 cult to say how many organic ones. This gas is the great 
 supporter of combustion. Substances that burn in air 
 burn much more vividly in pure oxygen, showing that the 
 oxygen in the air is the supporter of combustion. Iron 
 wire will burn in oxygen, but not in air ; and this is also 
 the case with other metals in a finely divided state. When, 
 by breathing, we inhale air into our lungs, a part of the 
 
oxygen it contains combines with carbon, and we exhale or 
 breathe out, as the result, an equal quantity, by volume, of 
 carbonic acid gas, and, consequently, liberate about 3J-J- 
 times as great a volume of free nitrogen gas. 
 
 Having glanced at the chemical constitution of the 
 atmosphere, let us next consider that of the principal gases 
 met with in coal mining. 
 
 CAKBONIC ACID GAS. 
 
 When this gas is met with in coal mines it is often 
 called styflw, choice-damp, or Hack-damp. It is composed 
 of oxygen and carbon. We have already considered the 
 nature of oxygen as a component part of the atmosphere, 
 but we must not expect to find it show the same properties 
 when chemically combined either with carbon or any other 
 substance whatever. Carbon, the other part of choke- 
 damp, forms the chief ingredient in coal; and coke con- 
 tains a still larger proportion of this substance; but the 
 diamond is pure carbon, in a crystalline state. The chemi- 
 cal composition of carbonic acid gas is 
 
 By Atoms. By Weight. By Volume. 
 
 Oxygen ... 2 ... 7273 percent. ... 1 
 Carbon ... 1 ... 27'27 ... 1* 
 
 1 condensed. 
 
 Now, although this gas contains nearly 3 parts out of 4, 
 by weight, of oxygen (the life-supporting element), yet, 
 because it is combined with another substance (carbon), the 
 result is, in this case, a poisonous gas. It is dangerous 
 to life to breathe air containing 8 per cent., or one-twelfth 
 
 * Bunsen assumes the hypothetical volume of carbon at one-half 
 of that assumed here; but 'as he gives its density at double the value 
 here given to it, the results are not altered. 
 
of this gas. Lights are extinguished in air containing 10 
 per cent., or one-tenth of it. At 32, under a pressure of 
 14' 7 Ibs. per square inch, 1,000 cubic feet of air weigh 
 80'728 Ibs., and 1,000 cubic feet of carbonic acid gas weigh 
 123*353 Ibs., so that it is rather more than lj times as 
 heavy as an equal volume of air. The special gravity of 
 air being 1,000, that of carbonic acid gas is 1528'01. 
 Before being mixed with air it rests next to the " thill," or 
 floor of mines, owing to its great heaviness or density when 
 compared with air. This gas, besides being given off 
 naturally in many mines, is always found to result from the 
 breathing of men and animals, the burning of candles and 
 lamps, and, mixed with other gases, from the explosion of 
 the powder used in blasting. Near the mouth of an adit 
 or drift at Butterknowle Colliery, in the County of Durham, 
 the writer has seen several small birds lying dead from the 
 effects of this gas. They had come to feed upon crumbs 
 where the workmen ate their meals, dose to the mouth of 
 this, an abandoned drift, and the gas coming out of the 
 drift at the level of the ground had overcome them. At 
 the same colliery, in several places where the coal has been 
 worked away, the ground has been rent up to the surface, 
 and it is said that birds flying across these rents or pit- 
 falls, in some instances, are so quickly affected by the 
 escaping gas as to drop into the holes and die there. 
 Without disputing the fact of dead birds being found in 
 the holes, the reason assigned as the cause of their coming 
 there appears to be rather doubtful. The effect of the gas 
 is not, perhaps, so instantaneous as to account for it. Un- 
 fortunately birds are not the only sufferers from this gas, 
 for many human beings have met their deaths through 
 breathing it; and in many other cases injurious effects 
 
are produced on the health of workmen through the 
 mixture of this gas, in small proportions, with the air of 
 mines. 
 
 Limestone consists of carbonic acid and lime, and chalk 
 is of a similar composition; these ingredients, however, 
 being generally mixed with oxide of iron, magnesia, and 
 other substances in less but variable proportions. 
 
 PROTO-CARBURETTED HYDROGEN GAS, 
 
 LIGHT CAEBUEETTED HYDEOGEN GAS, OE, AS IT IS SOMETIMES 
 CALLED, MAESH GAS. 
 
 This gas is the fire-damp of mines. It contains one 
 atom of carbon combined with two atoms of hydrogen, or 
 some multiple of these. Taking the atomic volumes of 
 carbon and hydrogen to be the same, it contains one volume 
 of carbon combined with two volumes of hydrogen in all 
 three volumes but the three volumes are condensed into 
 one volume of fire-damp. The weight of air at the tem- 
 perature of melting ice (32), and 14'7 Ibs. per square inch 
 pressure, is, for 1,000 cubic feet, 80'728 Ibs.; that of 1,000 
 cubic feet of gas, under the same conditions, is 45'368 Ibs., 
 so that the specific gravity of the gas is 562,* that of air 
 being 1,000, it being rather more than half as heavy as an 
 equal volume of air under the same conditions. Owing to 
 the fire-damp of mines being lighter than air it lodges next 
 the top or roof in mines until, by diffusion, it gets quite 
 mixed with the air. This gas would soon cause death if 
 breathed in a pure and undiluted state; but, when mixed 
 with twice its own volume of air, it may be breathed for 
 some time without serious effects. It quickly extinguishes 
 
 * Professor Bunsen gives the specific gravity of marsli gas at 
 55314, that of air being 1. 
 
lamps or candles when unmixed with air. Fire-damp, or 
 light carburetted hydrogen, contains nearly 25 per cent., 
 by weight, of hydrogen. Hydrogen is the lightest known 
 gas, being only one-fourteenth part of the weight of air. 
 The hydrogen in fire-damp is, however, condensed into a 
 smaller volume than it occupies in a free state. Light car- 
 buretted hydrogen gas is chemically composed of 
 
 By Atoms. By Weight. By Volume. 
 
 Hydrogen ... 2 ... 24'6 per cent. ... 2 
 Carbon ... 1 ... 75'4 ... 1 
 
 1 100 ... 1 condensed. 
 
 In the fire-damp of mines, however, we find a small pro- 
 portion of other gases mixed wica it. When 1 part of 
 fire- damp is mixed with 30 parts of air, by volume, its 
 presence can be detected by the appearance of the flame of 
 a candle; and as the quantity of fire-damp is gradually 
 increased from 1 up to 2 parts in 30 of the air, the appear- 
 ance of the flame is more and more affected by it; but even 
 in the latter proportion the mixture will not explode. The 
 flame of the candle is surmounted by a pale blue halo, 
 called in mining language a " top" or " cap," which par- 
 takes more or less of a brown colour, according to the quan- 
 tity of sty the or carbonic acid gas that may be present, 
 along with the fire-damp. The examination of the flame, 
 for the purpose of forming a judgment as to the quantity 
 of fire-damp mixed with the air, in mines, is, in mining 
 dialect, called " trying the candle" or " trying the lamp" 
 When the fire-damp forms as much as 1 part out of 13 of the 
 air, the mixture becomes explosive, so that, if ignited by an 
 exposed flame, the whole of the mixture is converted into a 
 mass of flame ; in this state of the mixture, however, the 
 
10 
 
 force of the explosion is comparatively feeble. When there 
 is only 9 to 10 times as much air as fire-damp, the explo- 
 sive force is greatest. If the proportion of gas be greater 
 than 1 part out of 9 to 10 of air, by volume, the force of 
 explosion gradually becomes less and less, until there is 
 only five times* as much air as gas, when the mixture 
 will no longer explode, but, on the contrary, will ex- 
 tinguish the flames of candles or lamps that may be brought 
 into it. 
 
 The presence of carbonic acid gas, or of free nitrogen 
 gas, in mixtures of fire-damp and air, is found to lessen 
 their explosive force ; so that if we add to the most explo- 
 sive mixture one-seventh part of its volume of carbonic acid 
 gas, it will not explode at all. Air containing one-fourth 
 part of fire-damp, by volume, may be breathed for some 
 time without very serious eifects being produced on the 
 animal frame. Common coal gas, as used for lighting, con- 
 tains a large proportion of light carburetted hydrogen gas 
 the fire-damp of mines. Besides this, however, it contains 
 a considerable proportion of pure hydrogen, some carbonic 
 oxide, and some olefiant gas. 
 
 When a mixture of air and fire-damp is exploded, the 
 chemical changes that take place, and the nature of the 
 resulting mixture, or after-damp, are as follows: 
 
 * " Even when mixed with three or nearly four times its bulk of 
 air it burnt quietly in the atmosphere, and extinguished a taper." 
 " When mixed with between 5 and 6 times its volume of air it ex- 
 piodcd feebly." " It exploded with most energy when mixed with 7 
 or 8 times its volume of air, and mixtures of fire-damp and air retained 
 their explosive power when the proportions were 1 of gas to 14 of air. 
 1 of carbonic acid added to 7, or 1 of nitrogen added to 6 parts of ex- 
 plosive mixture, rendered them inexplosive." From the Collected 
 Works of Sir II. Davy, page 10, Vol. VI., 1840. 
 
11 
 
 MIXTURE BEFORE EXPLOSION. 
 
 BT ATOMS, BT MEASURE. 
 
 Relative 
 
 No. of Volume Uncombined Combined Volume 
 
 Atoms, per Atom. Volume. Volume, per cent. 
 
 ^ {&::: 7 * 4 : I z^ } ** ** 
 
 Fir e.da m p...|^bo,> en . 1 x 2 - I 
 
 Free Nitre 
 Carbonic 
 Acid Gas 
 
 Steam .. 
 
 >gen 
 
 BY ATOMS. 
 Relative 
 No. of Volume Uncombined 
 Atoms, per Atom. Volume. 
 
 7'4 x 2 = 14-8 
 1 x 2 = 2 [ 
 2 x 1 = 2 J 
 2 x 2 = 4 ) 
 2 x 1 = 2 j 
 
 ( Carbon ( 
 | Oxygen \ 
 ( Hydrogen ( 
 ' 1 Oxygen ] 
 
 24-8 20-8 100-000 
 
 MIXTURE AFTER EXPLOSION. 
 
 BT HEASURE. 
 
 Combined Volume 
 Volume, per cent. 
 
 14-8 71-2 
 2 9-6 
 
 4 19-2 
 
 24-8 20-8 100-0 
 
 Before explosion, there may happen to be present either an 
 excess of air or of fire-damp, beyond what is necessary to 
 cause the explosion; and if so, they will remain naked with 
 the after-damp, in an unchanged state, after the explosion 
 has taken place. There never can, however, be such an 
 excess of air present as to render the after- damp fit to 
 breathe, or the explosion could not take place; the limits 
 are such that this is impossible. The above proportions of 
 1 of fire-damp to 9*4 of air, form th'e most explosive 
 mixture, all other proportions forming less explosive 
 mixtures. 
 
 From the second table, we perceive that the after- 
 damp contains between seven and eight times as much free 
 nitrogen as carbonic acid gas, or choke-damp. It was, at 
 one time, a popular mistake to suppose that the injurious 
 part of the after-damp consisted only of carbonic acid gas, 
 or choke-damp; not amongst scientific chemists, but 
 
12 
 
 amongst respectable mining authorities and that, not 
 very long ago. After-damp, it may be seen, by the second 
 table, contains about 71 parts of free nitrogen, 9J parts of 
 carbonic acid gas, and, at the moment of explosion, 19 parts 
 of steam ; so that it may be said, at this stage, that after- 
 damp contains, in round numbers, seven parts of nitrogen, 
 one part of carbonic acid gas, and two parts of steam, out 
 of a total of 10 parts. Directly after the explosion, a large 
 part of the steam condenses and leaves, as a residuum, about 
 7J parts of nitrogen and one part of carbonic acid gas, out 
 of eight and one-half parts ; the whole unfit to breathe, 
 and incapable of supporting either life or combustion. A 
 small excess of air, or of fire-damp, might be left mixed 
 with the after-damp of an explosion, beyond what is noticed 
 in the tables as being chemically changed ; but in no case 
 could the air of the after-damp contain less than twice its 
 own volume of deleterious gases, or the explosion could 
 not have taken place ; such a mixture, if breathed, would 
 soon cause death. Since explosions cannot always be pre- 
 vented, how important it is, then, to be prepared to mix 
 and dilute- the after-damp with fresh air, in as speedy a 
 manner as possible, after their occurrence. If there is more 
 fire-damp present than is chemically changed by an ex- 
 plosion, the force of the explosion itself is lessened, but the 
 after-damp resulting is more deadly than if an excess of air 
 had been present at the time of the explosion. 
 
 CARBONIC OXIDE. 
 
 This gas is sometimes called white damp, when met 
 with in mines. Assuming, as before, that the atomic volume 
 of carbon is twice as great as that of oxygen, its composition 
 is as follows : 
 
13 
 
 By Atoms. By Weight. By Volume. 
 Oxygen ... 1 ... 56'69 ... 
 Carbon ... 1 ... 43'31 ... 1 
 
 1 100 1 condensed. 
 
 Its specific gravity is 9 75' 19 5, that of air being assumed 
 at 1,000 ; so that 1,000 cubic feet of air at 32, and under 
 a pressure of 14' 7 Ibs. per square inch, weighing 80'728 
 Ibs., an equal volume of this gas under the same conditions 
 will weigh 79*426 Ibs., and one cubic foot under the same 
 conditions will, therefore, have a weight of '079426 Ibs. 
 
 Carbonic oxide has a much more deleterious effect on 
 the animal economy than carbonic acid ; air which contains 
 only one per cent, of carbonic oxide, almost immediately 
 causes the death of warm-blooded animals, as has been 
 shown by the decisive experiments of M. Felix Leblanc. 
 Carbonic oxide is itself an inflammable gas, but does not 
 support the combustion of other bodies. It has no taste, 
 but has a peculiar odour. Small animals immersed in it 
 die instantly. When inhaled, it produces giddiness and 
 fainting fits, even when mixed with a fourth of its bulk 
 of air. It is easy kindled, and burns with a blue flame, 
 being transformed into carbonic acid by the process. The 
 carbonic acid formed by combustion at the bottom of a 
 coal, coke, or charcoal fire is sometimes converted into 
 carbonic oxide, by being deprived of a part of its oxygen, 
 as it passes upwards through the red-hot embers ; and, on 
 coming in contact with the air at the top of the fire, burns 
 there with a blue flame, and is again converted into car- 
 bonic acid gas. This gas is, perhaps, never found in coal- 
 mines except as the result of the explosion of gunpowder, 
 or the combustion of coal or wood. Carbonic oxide is 
 
 B 
 
14 
 
 obtainable in a state of purity by heating yellow ferro- 
 cyanide of potassium, with eight or ten times its weight of 
 oil of vitriol. Bunsen obtained it by slightly heating a 
 mixture of formic and sulphuric acids ; and, to ensure the 
 perfect purity of the gas, he passed it through a concen- 
 trated solution of caustic potash. Such a proportion of 
 this gas might be mixed with air, as to form a mixture in 
 which candles or lamps would burn, while life would become 
 extinct ; and it is probable that many deaths in mines have 
 resulted from the gas in situations where the lights have 
 continued to burn. 
 
 It appears to be very probable that the deaths of the 
 men and boys in the late accident at Hartley Colliery arose 
 in a great measure from this gas given off by the furnace, 
 after the stoppage of the air-current by the closing of the 
 shaft ; inasmuch as the lights used by the workmen en- 
 gaged in clearing the shaft appeared to be rather increased 
 in brilliancy than otherwise at the time when the worst 
 effects were felt from the escaping gas ; and the mine gave 
 off no fire-damp, and very little choke-damp. 
 
 At page 120, in the minutes of evidence taken before 
 a select Committee of the House of Commons, on acci- 
 dents in mines, in 1835, the late George Stephenson, in 
 reply to question 1853, gives an account of an accident 
 at Newbottle Colliery, by which several persons lost their 
 lives by a gas in which the lights burnt well, and which 
 the witness supposed to have been sulphuretted hydrogen 
 gas ; but it appears to be more probable that it was a 
 mixture of carbonic oxide, sulphurous acid, and a small 
 quantity of carbonic acid gases, generated by the explosion 
 of gunpowder in the drift, where it was found to prevail j 
 
15 
 
 because sulphuretted hydrogen gas has a particularly offen- 
 sive smell of which no mention is made in the account of 
 the accident. 
 
 The writer is acquainted with several instances where 
 gases have caused deaths, and with others where they have 
 caused severe indisposition, in places where candles con- 
 tinued to burn brightly ; in some of these cases the gases 
 were apparently produced by the explosion of gunpowder, 
 and in others by the combustion of coals ; and hence it 
 appears to be probable that carbonic oxide was a prominent 
 ingredient in them. In an experiment by M# Leblanc, a 
 large-sized dog was asphyxiated in an atmosphere which 
 contained 4 per cent, of carbonic acid, and only ^ per cent, 
 of carbonic oxide. 
 
 HYDRO-SULPHURIC ACID, OR SULPHURETTED 
 HYDROGEN. 
 
 This gas is sometimes met with in coal-mines. It is 
 colourless, but distinguishable by its unpleasant smell, 
 which resembles that of rotten eggs. It produces fainting 
 fits and asphyxia, if inhaled, even when present only in 
 very small proportions with atmospheric air. When in^ 
 haled in its pure state it acts as a powerful narcotic poison, 
 It does not support combustion, but is itself inflammable, 
 and burns when exposed to a supply of air and ignited ; 
 and, when mixed with oxygen gas, the mixture is explosive. 
 It reddens tincture of litmus, but the reddening disappears 
 on exposure to the air. 
 
 The composition of sulphuretted hydrogen is as follows : 
 
 By Atoms. By Weight By Volume. 
 
 Sulphur 1 94*15 l-6th 
 
 Hydrogen 1 5'85 1 
 
 1 100 1 
 
16 
 
 According to Bunsen the specific gravity of this gas is 
 1174'88 ; that of air being assumed at 1,000, under the 
 same conditions as to temperature and pressure. Sulphur 
 heated strongly and repeatedly sublimed in fire-damp freed 
 from oxygen by phosphorus, produced a considerable en- 
 largement of its volume, sulphuretted hydrogen was formed, 
 and charcoal precipitated ; the volume of sulphuretted hy- 
 drogen produced (ascertained by absorbing it by solution 
 of potassa) was exactly double that of the fire-damp de- 
 composed. 
 
 Sulphuretted hydrogen gas may be inflamed by char- 
 coal or iron, even at a low red heat. In air it burns with 
 a blue flame, forming water and sulphurous acid, and de- 
 positing sulphur. According to some authorities, 1-1 500th 
 part of this gas in air is instantly fatal to small birds, 
 l-1000th killed a middle-sized dog, and a horse died in 
 an atmosphere that contained 1-2 50th part of its volume. 
 The presence of sulphuretted hydrogen gas in the atmos- 
 phere, even in small proportions, can be detected by its 
 action upon moist carbonate of lead, spread upon white 
 paper, which it blackens. M. Parent Duchatelet observed 
 that workmen breathed with impunity in an atmosphere 
 containing 1 per cent, of sulphuretted hydrogen, and he 
 states that he himself respired air containing as much as 
 3 per cent, of the gas, without experiencing any serious 
 results. This gas is formed whenever sulphur in a very 
 comminuted form is brought into cantact with hydrogen 
 in the act of being given off, and is probably formed, to 
 some extent, where pyrites is undergoing decomposition 
 in mines. When this gas is present with the air in mines, 
 candles will burn in the mixture, so that if it is not de- 
 
17 
 
 tected by its odour it may prove fetal to life before its 
 presence is detected. 
 
 It appears to be probable that this gas is frequently 
 formed in old unventilated workings partly filled with 
 water. There are two instances mentioned by Mr. Nicholas 
 Wood, in his evidence before the Committee of the House 
 of Commons on accidents in mines, in 1853 one at Hartley 
 Colliery, which proved fatal to one person, and another at 
 Tyne Main Colliery, where ill-effects where felt, notwith- 
 standing that the lights burnt well; both of which in all 
 likelihood were due to the generation of this gas from 
 the action of the water upon pyrites in old workings. 
 
 A man breathes into his lungs about one-fifth of a cubic 
 foot of air per minute, and converts about seven per cent, 
 (by volume) of this into carbonic acid gas, which, with 
 about three and three-quarter times as much free nitrogen, 
 he exhales, along with about 66| per cent, of the air he 
 breathes, in an unchanged state. The largest lamp used 
 in mining converts less oxygen into carbonic acid gas than 
 a workman. Both give off watery vapour as well as car- 
 bonic acid gas. When coal is on fire it gives off, in burn- 
 ing, carbonic acid, carbonic oxide, and sulphurous acid 
 gases. The explosion of gunpowder gives rise to carbonic 
 acid, nitrogen, carbonic oxide, and steam, besides car- 
 buretted and sulphuretted hydrogen in small proportions. 
 In the ordinary course of mining these causes give rise to 
 so small a quantity of gas, in proportion to the air, that 
 they hardly belong to the subject in hand, unless in refer- 
 ence to the state of a confined and unventilated part of a 
 mine, where a shot has been fired, or in the more rare case 
 of coal being on fire in a mine. 
 
18 
 
 Sir Humphrey Davy discovered that the flame of ignited 
 gas would not pass through fine wire gauze containing 28 
 holes for' each inch in length, or 784 holes per square inch, 
 unless the gas is moved with great velocity against the 
 gauze, or the gauze against the gas; and by enclosing the 
 flame of an oil lamp in a cage made of this gauze we are 
 able to carry a light into an explosive mixture of air and 
 gas without setting the gas on fire on the outside of the 
 gauze. By this means an explosion is avoided. If we 
 find ourselves with a safety-lamp in an explosive atmos- 
 phere, we should only try to put out the flame by carefully 
 drawing down the wick, and by no means try to blow 
 it out, or we might blow the flame through the gauze and 
 cause an explosion. An explosion might result .from 
 drawing the flame of the lamp through the gauze by means 
 of a tobacco pipe; yet workmen are not unfrequently de- 
 tected in this very daring and dangerous practice in mines. 
 Outside-feeding or oil-tubes used to be attached to safety- 
 lamps, but these are dangerous, as the flame might pass 
 down the wick tube and up the oil tube, and so fire the 
 gas on the outside of the lamp, if the oil plug was out or 
 fitted badly, and the wick was small compared with the 
 tube; but feeding tubes are not used now, at least in many 
 districts. There are several sorts of safety-lamps now more 
 or less used, which give more light than the Davy-lamp ; 
 glass being used in lieu of gauze opposite the flame. 
 Glass is brittle and liable to crack from unequal expansion, 
 and many persons do not think glass lamps so safe as the 
 Davy in consequence. The late George Stephenson con- 
 trived a safety-lamp, having both glass and gauze around 
 the flame, known as the Geordy, or Stephenson-lamp. The 
 
19 
 
 Davy-lamp is perhaps the best known lamp for detecting 
 the presence of a small mixture of fire-damp in the air of 
 a mine. 
 
 Now, since fire-damp, choke-damp, and other gases are 
 met with in more or less abundance in all coal mines, it 
 becomes an important question as to how the bad, and 
 often fatal, effects they are likely to produce if not properly 
 dealt with may best be avoided. To this end it has some- 
 times been proposed to get them to combine chemically 
 with some substance to be presented to them as they are 
 given off ; and only a short time ago, a Mr. Wall had a 
 proposition of this kind before the public. So far; however, 
 the best mode of dealing with them appears to be to dilute 
 them with very large quantities of fresh air, and to sweep 
 them out of the mine by an energetic ventilation as fast as 
 they are given off or generated. After all, however, the 
 natural laws and principles operating in the production of 
 ventilation in mines have been less generally studied in 
 England than on the Continent, and from this cause many- 
 mistakes have been made in the practice of ventilation in 
 this country. New arrangements for the ventilation of 
 mines have sometimes been made at great cost, and have 
 not been found to answer when completed. In a few cases 
 lives have been lost from this cause ; in others an inferior 
 arrangement and ventilation have been produced, where, 
 by the application of these natural principles, a superior 
 one might have been obtained at the same or even at a 
 smaller cost. Many, if not all the members of this Society, 
 are familiar with the details of the general practice of venti- 
 lation as pursued in this country. Instead, therefore, of 
 considering this part of the subject, it is here proposed 
 
20 
 
 rather to direct attention to the natural laws and principles 
 affecting the ventilation of mines. 
 
 NATURAL LAWS AND PRINCIPLES AFFECTING THE 
 VENTILATION OF MINES. 
 
 As an introduction to the general laws and principles 
 affecting the ventilation of mines, let us notice some of the 
 general physical properties of air and gases. The world, 
 on the surface of which we live, is a large globe, about 
 8,000 miles in diameter, and 25,000 miles in circumfer- 
 ence. This great globe is surrounded by, and enclosed 
 in, an atmosphere of air many miles in depth, so that the 
 surface of the earth where we live is the bottom of a deep 
 sea or ocean of air. Air is composed of the two gases, 
 oxygen and nitrogen, in the proportions that have been 
 named. Air and all gases have the following physical 
 properties : They are impenetrable. If any space be filled 
 with air, no other material body can occupy the same 
 space without first displacing the air, because no two mate- 
 rial bodies can be in the same place at the same time. Two 
 gases, or a gas and a vapour, may fill the same space (in a 
 certain sense) by being mixed with each other, in the same 
 manner that a sponge will hold water, but each gas or vapour 
 must leave spaces vacant for the other to occupy or fill. Air 
 and gases are possessed of the property called inertia. With 
 respect to motion and rest, air, gases, and indeed all kinds 
 of matter, are said to be inert, so that they will remain 
 either at rest or in the same state of motion, until acted 
 upon by some force or resistance. This property merely 
 implies what may be termed a negative quality, of such a 
 character as tt> have the effect of causing matter not to 
 
21 
 
 change its state, whether of motion or of rest, without som-' 
 force or resistance being applied to it to cause it to do so. 
 Owing to the property of inertia, a body will remain either 
 at rest or in the same state of motion, both as to speed and 
 direction, in spite of any forces or pressures that may be 
 acting upon it, provided they are equal and opposite forces, 
 so as to counterbalance each other This is the state of the 
 atmosphere in a calm : there is always a pressure in every 
 direction, up, down, sideways, diagonally, and in fact in 
 every direction, in the air of the atmosphere. This pres- 
 sure arises from the mere weight of the superincumbent air, 
 and amounts generally to nearly one ton on each square 
 foot, or 14 Ibs. and upwards per square inch. If the pres- 
 sure is lessened on one side, the ordinary pressure upon the 
 opposite side drives the air towards the side where the 
 pressure is reduced, and gives rise to a wind. If the 
 pressure is increased on any side, the air is driven away to 
 the opposite side, against the ordinary pressure. Air in 
 motion cannot properly be said to have any more pressure 
 or tension than the still air through which it moves. What 
 would otherwise be extra pressure is really converted into 
 motion in the air. Any excess of pressure really existing 
 is simply that due to the friction which the air encounters 
 in moving. This is a fact not always understood, and not 
 always acknowledged, even in works pretending to treat 
 the subject upon scientific principles. Force may be con- 
 verted into mere motion without at all increasing the 
 tension or spring of the air to which it applied ; if it does 
 increase the pressure on the air, it is only to the extent 
 of the resistance encountered. Air in motion is called 
 "wind ;" and owing to its inertia it will only lessen its 
 speed by meeting with frietional resistances, or by giving 
 
22 
 
 out its force to obstructions, such as the surface of the 
 earth, houses, trees, wind-mills, and other objects ; and in 
 every case where power is taken out of the wind, it is done 
 at the expense of lessening its velocity. If, for instance, 
 we should make the wind passing through a mine drive a 
 mill, we would thereby lessen the force and quantity of wind 
 circulating in the mine, in a given time, if the pressure 
 causing ventilation remained constant. Eailway trains at 
 high speed, even in a calm, meet with a large share of their 
 resistance from the air the trains lose force, and the air 
 gains what they lose. Owing to the inertia of the air, birds 
 meet with such a resisting medium in it as to give them a 
 fulcrum or resting place for their wings, and enable them to 
 fly. This property of inertia belongs alike to all material 
 bodies, and may, in general terms, be called an unwillingness 
 to move, when at rest, or to change their speed or direction of 
 motion when they are moving, without a force or resistance 
 being applied to cause them to do so. Air is compressible. 
 Air is squeezed and contracted into less and less bulk as we 
 increase the pressure upon it. If we double the pressure 
 (without changing the temperature), the same air only fills 
 one-half of the space ; and if we treble the pressure, it only 
 fills one-third of the space ; and if we apply four times the 
 pressure, it only fills one fourth of the space, and so on, 
 provided that the heat or temperature of the air remains 
 the same. This is called the law of Mariotte, or Boyle. 
 The air at the surface of the earth is generally pressed by the 
 whole of the air above it, to an extent measured by 29*922 
 inches of mercury (reckoned at the density due to melting 
 ice, 93), as shown by our common barometers ; a pressure 
 equal to 2116'4 Ibs. per square foot. To give this pressure 
 we should require the air of the atmosphere to be 26,216 
 
23 
 
 feet high, if it was all as heavy as the air at the earth's 
 surface. The fact is, however, that the air, as we go up, 
 is pressed by less and less air above it, and owing to its 
 elasticity or -spring becomes lighter and lighter ; so that 
 instead of 26,216 feet, or nearly five miles high, the atmos- 
 phere is immensely higher. It gets so much thinner, rarer, 
 or lighter, that at 
 
 3 miles above the surface of the earth it is 2 times rarer. 
 
 74, 
 
 
 14 16 
 
 21 64 
 
 28 256 
 
 35 1,024 
 
 And so on. If we carry a barometer up a hill, we have 
 less and less air above us, and its pressure will, therefore, 
 support less and less height of column of mercury, and 
 hence the barometer falls. If we take it down into a mine 
 we get a longer column of air above us, and it supports a 
 longer column of mercury, so that the barometer rises. 
 In ordinary states of the weather mercury is about 10,800 
 times as heavy as the same volume of air near the surface 
 of the earth, and hence above 900 feet, or 150 fathoms, of 
 ascent or descent, makes a change of one inch of mercury 
 in the height of the barometer. This fact has been applied 
 to measure the height of mountains by means of barometers, 
 and it has sometimes been employed to estimate the friction 
 of air in shafts. The difference between the height of the 
 barometer at the top and the bottom of a pit 150 fathoms, 
 or 300 yards in depth, is about one inch of mercury. 
 
 Air is elastic ; it is a perfect spring, so that whatever 
 
 force compresses it is an exact measure of the force it will 
 
 pring out with, if we take away the compressing force. 
 
24 
 
 The air, at the surface of the earth, is pressed at about 
 14'7 Ibs. per square inch, and if we take half this pressure 
 off it will swell out to twice its previous bulk ; if we take 
 away three-fourths of this pressure, and only leave one- 
 fourth, the same air will swell out and fill four times the 
 space it previously occupied, and so on. Whatever force 
 or power is expended in compressing air into less bounds, 
 will be given out as force or power by the same air, in 
 swelling out to its former volume, when we take away the 
 pressure so applied. 
 
 Air has weight, like all other material bodies. The 
 weight of a vessel filled with air is greater than its weight 
 when the air is pumped out of the vessel. A tall column 
 of air, one foot square, and of the full height of the atmos- 
 phere, weighs nearly one ton. Another column of the same 
 height, and one inch square, weighs rather more than 
 fourteen pounds. The weight of the atmosphere enables 
 it to support a column of water nearly 34 feet high, or one 
 of mercury nearly thirty inches high ; and this pressure 
 acts equally in all directions up, down, sideways, and 
 in fact in every direction. The body of a man of average 
 size is pressed by nearly thirteen tons weight from this cause. 
 
 The direction, speed, and force of the wind, depend upon 
 the amount of the difference of pressure that gives rise to it, 
 and in general has little or no connection with the gross 
 amount of the pressure acting in the direction of the wind, 
 because a large share of that pressure is counterbalanced by 
 an equal pressure acting in the opposite direction. 
 
 In the open air, the velocity of the wind is the same as 
 the velocity that a body would acquire by falling from the 
 top to the bottom of such a column of air of equal density 
 as by its weight would produce the same pressure as that 
 
25 
 
 which gives rise to the wind. For instance, if the state of 
 the air as to the temperature and pressure is such that there 
 is a pressure of 2,000 Ibs. (which is nearly a ton) on each 
 square foot in one direction, and only 1,999 Ibs. per foot, 
 or one pound per foot less, in the opposite direction, when 
 13 cubic feet of air weigh 1 lb., then the difference of 
 pressure giving rise to the wind is equal to 1 lb. per square 
 foot ; and a column of air 1 foot in area and 13 feet high 
 would weigh 1 lb. But a body falling through a height of 
 13 feet, under the force of gravity, would acquire a velocity 
 of 8*02 times the square root of 13, or 28 '9 feet per second ; 
 and this is, therefore, the velocity of a wind in the open air, 
 due to a pressure, or rather to a difference of pressure of 1 
 lb. per square foot, when the total pressure of the atmosphere 
 is nearly 2,000 Ibs. per square foot, and 13 cubic feet of air 
 weigh 1 lb. If we wish to find the velocity of such a wind 
 in the open air as is due to a known difference of pressure 
 on each square foot, we have first to find how many cubic 
 feet of the air is equal in weight to the difference of pressure 
 on a square foot which gives rise to the wind ; and eight 
 times the square root of this number is equal to the velocity 
 of the wind in feet per second. In like manner, if we 
 would find the pressure giving rise to a wind when we know 
 its velocity, we must square the velocity in feet per second, 
 and divide the result by sixty-four and one-third, and the 
 quotient will be the height in feet of an air column giving 
 rise to the wind ; this height being divided by the number 
 of cubic feet of air weighing one pound will give the differ- 
 ence of pressure in pounds per square foot giving rise to 
 the velocity. This rule is merely the reverse of the former 
 one. A difference of pressure of only one pound to the 
 square foot, under the conditions before stated, gives rise 
 to a wind in the open air, having a velocity of 28-8 feet 
 
26 
 
 per second, or more than nineteen miles per hour, which is 
 nearly equal to the highest velocity of the air in the upcast 
 shafts of coal mines. 
 
 In practice, in the ventilation of mines, it is found to 
 be necessary to employ a very much higher pressure than 
 one pound to the square foot in order to give rise to this 
 velocity ; it is, indeed, in many instances necessary to employ 
 from ten to twenty pounds per square foot to do so, and 
 this pressure is equal to the. weight of an air column 130 to 
 260 feet high, instead of only 13 feet high as in the open 
 air. It has been a very common mistake to consider that 
 this difference shows a discrepancy between theory and 
 practice. It shows no such thing. The true theory of any 
 subject embraces in its grasp all the causes that operate, 
 and can never fail to agree with practice if it is really the 
 true and complete theory. Theory, indeed, is a collection 
 of general principles, gleaned or generalized from observation 
 of the result of practical trials or experiments ; and it is either 
 a false or an incomplete theory that does not embrace the 
 whole of the general principles involved in any pheno- 
 menon we may observe. It would be true, and therefore 
 much more becoming, in such cases, to say that we do 
 not understand the true theory, because the hypothesis or 
 supposition we have adopted does not agree with what 
 we notice to occur in practice ; and this ought to set us 
 to work to try to find out what is the true theory of the 
 matter, because practice, when not guided by general 
 principles, is mere guess-work or empiricism, so far as 
 regards every case excepting only that in which the ob- 
 servation itself is made. 
 
 The reason of from ten to twenty times the amount of 
 force or pressure that is required to generate any velocity 
 in the open atmosphere, often being required to give rise 
 
27 
 
 to the same velocity in the air in mines, arises from the 
 friction that air meets with by rubbing against the sides 
 of the air-ways in passing through mines. Every square 
 foot of surface exposed to the air travelling along the gal- 
 leries of a mine is pressed by the air to the extent of about 
 a ton of force or pressure, and it is therefore no wonder 
 that extra pressure is required to overcome the friction 
 arising from this immense pressure. If, for instance, we 
 find that the last or final velocity of air escaping from 
 a mine by an upcast shaft is such as to require a pres- 
 sure of one pound per foot, or thirteen feet of air column, 
 to give rise to it, on the supposition that there were no 
 friction ; and if, at the same time, we find that the actual 
 pressure employed is ten times as much, or ten pounds 
 per square foot, we learn from this that nine pounds out 
 of the ten pounds per foot are required to overcome the 
 friction of the air in rubbing against the sides of the air- 
 ways, the other one pound per foot, or one-tenth of the 
 whole pressure only, being required to give rise to the 
 velocity; and this is no uncommon case in the practice 
 of the ventilation of coal mines. Friction, then, arising 
 from the air rubbing against the top, bottom, and sides of 
 the air-ways in mines, is really the greatest obstacle to be 
 overcome by the ventilating pressure or power, the force 
 required to put the air into motion, apart from friction, 
 being very small in comparison, at least in a large majority 
 of cases, particularly in coal mines, which generally require 
 a much more energetic ventilation than is necessary for the 
 salubrity of metallic mines. 
 
 To show the comparative amounts of pressure expended 
 upon creating velocity in the air, and upon overcoming the 
 frictional resistance it meets with in mines, respectively, 
 the following cases are cited, the pressures due to velocities 
 
28 
 
 being those due to the final velocities at the tops of the 
 
 upcast shafts. 
 
 
 Pressure in 
 Air Column 
 due to 
 Velocity, 
 
 Pressure in 
 Air Column 
 due to 
 Friction. 
 
 Total 
 Pressure 
 Employed. 
 
 Proportion 
 due to 
 Velocity and 
 Friction 
 respectively. 
 
 Hetton Colliery, 1st case 
 Do. Do. 2nd case 
 Has well Colliery 
 Tyne Main Do 
 
 Feet. 
 10-43 
 12-37 
 13-84 
 25-70 
 
 Feel. 
 
 179-88 
 21263 
 140-66 
 177-50 
 
 Feet. 
 190-31 
 225-00 
 154-50 
 203-20 
 
 1 : 18 
 1 : 17 
 1 : 10 
 1:7 
 
 From this it will be seen that out of a total pressure of 
 nineteen, at Hetton Colliery, no less than eighteen were 
 employed on friction, and only one upon the velocity of 
 the air. 
 
 At Haswell Colliery, ten parts out of eleven of the ven- 
 tilating pressure were spent upon the friction of the air, 
 and only one part out of eleven upon creating its final 
 velocity at the top of the upcast shaft. 
 
 At Tyne Main Colliery, seven parts out of eight of the 
 ventilating pressure were spent upon friction, and only one 
 part in eight upon the velocity of the air at the top of the 
 upcast shaft. 
 
 From these examples it will be perceived that the amount 
 of ventilation in mines, and, therefore, the safety, health, 
 and comfort of the workmen employed in them, depend 
 almost entirely upon the amount of friction that the air 
 meets with, under any mode of ventilation we may employ ; 
 and hence, the great importance of understanding the 
 general laws and principles upon which the friction of air 
 in mines depends, so that we may know how to reduce such 
 friction to its lowest possible amount, and by this means 
 obtain the greatest quantity of air, from any ventilating 
 power we may employ. 
 
ON THE 
 
 FKICTION OF AIK IN MINES, 
 
 THE amount of friction is reckoned or estimated by the 
 amount of the pressure or force required to overcome it. 
 Numerous experiments have been made to find out the 
 laws that govern the friction of air and gases, both in 
 pipes having an uniform section, and, to a less extent, in 
 the irregular air-ways of mines. By these experiments, 
 the following laws have been found to hold good in prac- 
 tice. 
 
 The pressure required to overcome the friction of air 
 increases and decreases in exactly the same proportion 
 that the area or extent of the rubbing surface, exposed to 
 the air, increases or decreases ; so that when the velocity 
 of the air, and the sectional area of the air-way, remain 
 the same, the pressure required to overcome the friction 
 is proportional to the area or extent of the rubbing sur- 
 face exposed to it; and hence, if we double or treble the 
 extent of the rubbing surface, we also double or treble the 
 friction, or, what is the same, the force or pressure re- 
 quired to overcome it. The rubbing surface, of course, 
 depends upon the circumference or perimeter of the air- 
 way, and upon its length. The rubbing surface is found 
 by multiplying the perimeter by the length of the air- 
 way, where it has an uniform section. A circular pipe or 
 air-way offers less rubbing surface, for the same length, 
 than any other form or shape of air-way of equal sectional 
 
30 
 
 area ; because the circumference of a circle is less, in pro- 
 portion to its area, than the perimeter of any other figure 
 is to its area. A circle whose area is 1 has a circumference 
 of 3*545, or rather more than 3J; the perimeter of a 
 square is 4, when its area is 1 ; so that about 7 yards of 
 square pipe would offer the same resistance as 8 yards 
 of round pipe, having an equal size or area of section, when 
 the same quantity of air passes through them in a given 
 time. 
 
 It is true that the friction of air or gas, in passing 
 through the same pipe or air- way, varies in just the same 
 degree that the density of the air or gas may vary ; but 
 in air-ways in coal-mines the air has always nearly one and 
 the same density, and it is only in particular calculations 
 that it becomes requisite to notice its changes of density, 
 in reference at least to this part of the general subject, since 
 they are so small in amount. This is the case as regards 
 friction, but the effects of variations in the density of the 
 air circulating in mines are more sensible in producing pres- 
 sure, operating either in favour of, or against the ventilating 
 pressure, in rise or dip workings ; but these effects belong 
 more especially to another part of the subject. In an air- 
 way 5 feet square, the perimeter of the section is 4 x 5 = 20 
 feet; and if it is 1,000 long, the rubbing surface is 20 X 
 1,000 = 20,000 square feet. In an air-way 10 feet square, 
 the perimeter of the section is 4 x 10 = 40 feet ; and if it 
 was 1,000 long, the rubbing surface would be 40 x 1,000 
 = 40,000 feet ; so that on comparing the two cases it will 
 be apparent that for four times the area there is only two 
 times the extent of rubbing surface. If such an air-way as 
 that last mentioned (10 feet square, and having a rubbing 
 surface of 40,000 square feet for every 1,000 feet in length) 
 
31 
 
 
 5 
 
 5 
 
 
 5 
 
 5 
 
 5 
 
 5 
 
 
 5 
 
 5 
 
 
 
 5 
 
 5 
 
 
 5 
 
 5 
 
 5 
 
 5 
 
 
 5 
 
 5 
 
 
 were divided into four equal-sized square air-ways, the 
 rubbing surface exposed to the moving air would be ex- 
 10 actly double by the division ; 
 
 and there would be 20 feet 
 of perimeter for each of the 
 four air-ways, or 80 feet on 
 10 the whole; so that for a length 
 of 1,000 feet, the rubbing sur- 
 face for the four small air- 
 ways would be 80,000 square 
 10 feet ; or, exactly twice as great 
 
 as that for the one large air-way, although the united areas 
 of the smaller air- ways would be exactly equal to that of a 
 single large one. In one case there would be a single air- 
 way 100 feet in area ; and in the other four smaller air-ways, 
 each 25 feet area ; but the rubbing surface, and therefore 
 the friction and the pressure required to overcome it for 
 the same gross quantity of air, would be twice as great in 
 the four small as in the one large air-way having the same 
 area. And from this fact we learn that one large air-way 
 is preferable to a number of smaller ones, even if they to- 
 gether make up the same sectional area or size. In prac- 
 tice it often happens, however, that a number of smau air- 
 ways can be made and maintained at a less cost than one 
 large air-way, presenting an equal sectional area ; and, in 
 such cases, a few extra air-ways of small area may more 
 than compensate in utility, and make up in cost for the 
 absence of one extra-sized air-way ; and hence the futility 
 of insisting upon the sectional area of air-ways in mines 
 being of any particular amount, without specifying their 
 number, beyond requiring that one at least in each split 
 be large enough to admit of persons travelling in it. The 
 
32 
 
 same principle may be illustrated by taking two air- ways of 
 equal size or sectional area, but having different forms or 
 shapes of section ; supposing one of them to be 10 feet high 
 and 10 feet wide, its size or area of section would be 10 x 10 
 = 100 feet ; and supposing the other air-way to be 20 feet 
 wide, but only 5 feet high, the area would be the same (or 
 5 X 20) 100 feet. 
 10 _ 
 
 20 
 
 20 
 
 The air-way 10 feet square would have a perimeter of 
 section 4 x 10 = 40 feet, while the other would have a 
 perimeter of (20 + 20 + 5 + 5) 50 feet, compared with 
 only 40 in the former ; so that for equal lengths the fric- 
 tion of the air would only be 40 in the square air-way, 
 compared with 50 in the oblong one ; and the friction in 
 50 yards of length, in the square-shaped air- way, would be 
 no more than that in 40 yards of length in the oblong one 
 for the same quantity of air. Since the air in a mine presses 
 with nearly the same force upon every square foot, it is 
 quite natural that the frictional resistance should be greater 
 or less in amount, to the same extent that the rubbing 
 surface or number of square feet exposed to the air is 
 greater or less; and this is the general law or principle 
 that has just been stated and illustrated by examples. 
 
 The pressures employed to ventilate mines are com- 
 monly reckoned at so much per square foot of area, and 
 not by the entire pressure employed, which is equal to the 
 number of square feet multiplied by the pressure on each 
 
33 
 
 square foot of sectional area in the shaft or air-way. For 
 instance, a ventilating pressure of 10 Ibs. to the square foot 
 on an air-way 100 feet in area is equal, on the whole, to 
 10 x 100 = 1,000 Ibs. If the same pressure of 10 Ibs. 
 per foot is applied to an air-way of only 50 feet area the 
 total pressure is only 10 x 50 = 500 Ibs. ; owing to the 
 area being one-half, the total or gross pressure is also only 
 one-half. In order to get the same total pressure, we must 
 make the pressure per foot greater in the same proportion 
 that the area is less, when the rubbing surface and velocity 
 of the air are to be the same in two cases. If we reckoned 
 ventilating pressure by its total amount we would not re- 
 quire to notice this law, it is so self-evident ; and it is only 
 because we speak and treat of it as so much pressure per 
 square foot that we require to consider the number of square 
 feet to which it is applied. If there were two air-ways, one 
 just twice the area of the other, the velocity of the air and 
 the extent of rubling surface being the same in each, then 
 we must apply twice the pressure, to each square foot of 
 the small one, that is required by the larger one, to over- 
 come the equal amount of friction in the two air-ways, the 
 quantity of air passing in the smaller one being just one- 
 half of that in the larger. As an example, if we had an 
 air-way 10 feet by 10 feet the area would be 100 feet, and 
 the perimeter of section 40 feet ; and another air-way 5 feet 
 high by 15 feet wide, the area would be 75 square feet, or just 
 | of the area of the former ; the perimeter of section would 
 
 10 _ 
 
 15 
 
 100 10 75 
 
84 
 
 be, however, exactly 40 feet in both air- ways. In the larger 
 air-way we would only require to employ 3-4ths of the 
 pressure on each foot of surface (that is to say 3-4ths of 
 the water gauge) that we would require to employ on each 
 foot of the smaller area, so as to make up the same total 
 ventilating pressure the rubbing surface for an equal 
 length of air-way being the same in the two cases, because 
 the perimeter of their sections are equal, and the velocity 
 of the air being taken as the same in the two cases, the 
 quantities of air per minute would be simply proportional 
 to their respective areas under these circumstances. 
 
 This second law relating to the friction of air in mines 
 need not have been noticed at all if we had reckoned venti- 
 lating pressure as a whole : but as we generally speak of it 
 as so many pounds per foot, w r e must also take into account, 
 as has previously been remarked, the number of square feet 
 to which it is applied, that is, the area of the section of the 
 air- way, in the same manner that the area in inches of the 
 cylinder or piston of a steam engine multiplied by the pres- 
 sure on each square inch gives the total force applied to the 
 piston. An inch of water column, as shown by a water- 
 gauge, represents a pressure of about 5*2 Ibs. per square 
 foot. 
 
 The third general law relating to the friction of air in 
 mines is, that the pressure required to overcome the friction 
 in the same air- ways, varies (that is to say, increases or de- 
 creases) in the same proportions that the square of the 
 velocity of the air increases or decreases ; so that a double 
 velocity of air, in the same air-way, meets with a double double, 
 or fourfold resistance ; a treble velocity meets with a treble 
 treble, or ninefold resistance ; and a velocity of four times 
 as great gives rise to a resistance four times four, or sixteen 
 
85 
 
 times as great. In the same way a half velocity meets with 
 one-half of a half, or l-4th of the resistance ; l-3rd of the 
 velocity encounters only a third part of a third, or l-9th 
 of the friction, and so on. 
 
 The third law of friction, at first sight, looks rather com- 
 plex. Consideration, however, shows it to be quite natural, 
 because, if we double the velocity of the air in the same 
 air-way, we in the first place cause twice the quantity of air 
 to meet the resistance in a given time ; and, in addition to 
 this, every part of this double quantity meets every resist- 
 ance with a double velocity or momentum; the double 
 quantity of air, and the double velocity taken together, may 
 well be supposed to give rise to a double double, or fourfold 
 resistance ; and this is the true law. Again, if we treble 
 the velocity of the air, we thereby cause three times the num- 
 ber of particles to meet the resistances in each moment of 
 time, and this alone should treble the resistances ; but, in 
 addition to this, the treble quantity meets the resistances 
 with three times the speed or momentum, which trebles the 
 threefold resistance that arises from the threefold number of 
 particles of air that meets the resistances each moment of 
 time ; on the whole, making a ninefold resistance for a three- 
 fold quantity of air in a given time. 
 
 The laws of ventilation would be very simple, quite as 
 simple, indeed, as they are natural, were it not that, in lieu 
 of the mere quantity of air circulating in a given time, or 
 the mere velocity of the air, we must make use of the square 
 of the quantity, or, what is the same, the square of the 
 velocity in our calculations ; and, as a matter of course, in 
 calculations for comparative results, if we employ the squares 
 of the quantities or velocities, we must expect, as results, 
 not the quantities or the velocities simply, but their squares; 
 
36 
 
 and, therefore, it will be necessary to extract the square roots 
 of the results so obtained in order to get at the simple quan- 
 tities themselves. 
 
 It has already been stated, that there is one other prin- 
 ciple bearing on the friction of air passing through mines, 
 to the effect that it is greater or less in the same proportion 
 that the density or weight of each cubic foot of air is greater 
 or less ; so that if each cubic foot of air had a double weight 
 it would have a double amount of friction ; or, if it had 
 only half the weight it would have only half the amount of 
 friction in the same air-way, when the velocity or the num- 
 ber of cubic feet per minute is the same ; but the variations 
 in the density of the air in mines are so very small, com- 
 pared with the whole density, that the effects of this law on 
 the amount of ventilation are very small so small, indeed, 
 as to be practically unfelt, at any rate as an increase or re- 
 duction of friction in the moving air; even in an upright 
 or vertical shaft the density of the air would only be altered 
 on the average by about l-60th part of its amount, com- 
 pared with a level air- way, supposing the shaft to be 150 
 fathoms deep, so far as the pressure of the atmosphere is 
 concerned. The changes of density arising from the heat 
 of upcast shafts, in expanding the air, have a greater effect, 
 so far as such shafts alone are concerned, under furnace 
 ventilation ; but this does not affect the friction of the air 
 in the workings of the mine ; and, even in these shafts, the 
 lessened density, arising from expansion by heat, has its 
 effects on reducing the shaft friction greatly modified, by 
 the greater velocity due to the increase in the volume of 
 the air ; this increased velocity does more than make up, by 
 the accompanying increase of friction, for any reduction in 
 such friction that is due to the lessened density of the air 
 
37 
 
 in every case ; the friction, in fact, increases or decreases in 
 just the same proportion that the volume of a given weight 
 of air increases or decreases, whether the change of density 
 arises from change of temperature or from change of pres- 
 sure. Supposing the temperature of the air in a mine to be 
 60 in winter, and 65 in summer, on the average, such a 
 change would only alter the friction in such mine by about 
 l-104th of its amount. In summer the friction would be 
 1-1 04th greater than in winter for the same weight of air, 
 but it would, at the same time, be about l-104th part less 
 for the same volume of air, an alteration hardly worth no- 
 tice for the present purpose. The total friction or the total 
 pressure due to the friction of air rubbing against the top, 
 bottom, and sides of the air-ways of mines is not very well 
 ascertained ; all the experiments, at least all that have come 
 under my notice as having been made for the purpose, have 
 been in some respects of a rude character, the necessary 
 particulars not being given in the accounts published to fix 
 with rigid accuracy its amount. 
 
 For the best accounts of such trials, it seems probable 
 that for every foot of rubbing surface, and for a velocity in 
 the air of 1,000 feet per minute, the friction is equal to 
 0*26881 feet of air column of the same density as the flow- 
 ing air, which is equal to a pressure, with air at 32, of 
 0'0217 Ibs. per square foot of area of section ; calling this 
 the co-efficient of friction, we have the following rules with 
 respect to the friction of air in mines: 
 
Jcsv* 
 
 88 
 
 Where p 
 
 Rubbing surface 
 
 -ff 
 
 (2) 
 
 Velocity squared 
 
 V * = Jcs~ 
 
 (3) 
 
 Co -efficient of 
 friction 
 
 * = f^ 
 
 '(*) 
 
 Pressure per foot 
 
 _ Icsv* 
 a 
 
 (5) 
 
 Area of section 
 
 Icsv* 
 
 (6) 
 
 
 p 
 
 
 pressure per sq. foot. 
 
 a = sq. feet of sectional 
 area. 
 
 s = the area of rubbing 
 surface exposed to 
 the air. 
 
 v the velocity of the 
 air in thousands of 
 feet per minute 
 1,000 ft. per minute 
 being taken as the 
 unit of velocity. 
 
 k = the co-efficient of fric- 
 tion in the same 
 terms or unit as p is 
 taken in. 
 
 Putting these formulae into words, we have the follow- 
 ing set of rules: 
 
 (1.) To find the total pressure* due to friction Multi- 
 ply the co-efficient of friction by the extent of the rubbing 
 surface, and the product by the square of the velocity in 
 thousands of feet per minute ; that is to say, by the square 
 of the quotient resulting from dividing the velocity in feet 
 per minute by 1,000. 
 
 (2.) To find therubUng surface. Divide the total pres- 
 sure by the product of the co-efficient of friction, and the 
 square of the velocity in thousands of feet per minute. 
 
 (3.) To find the velocity. Divide the total pressure by 
 the product of the co-efficient of friction, and the rubbing 
 surface this gives the square of the velocity the square 
 root of which is the velocity itself, in thousands of feet per 
 minute j this multiplied by 1,000 will give the velocity in 
 feet per minute. 
 
 (4. ) To find the co-efficient of friction from experiments. 
 Divide the total pressure by the rubbing surface, and the 
 
 * The total pressure, in these rules, is found by multiplying the 
 sectional area of the air-way, in feet, by the pressure per square foot. 
 
89 
 
 square of the velocity (in thousands of feet per minute) 
 multiplied together. 
 
 (5.) To find the pressure on each foot of section. Mul- 
 tiply the co-efficient of friction, the rubbing surface, and 
 the square of the velocity (in thousands of feet per minute) 
 all into each other, and divide the product by the area of 
 the section. 
 
 (6.) To find the area of the section. Multiply the co- 
 efficient of friction, the rubbing surface, and the square of 
 the velocity (in thousands of feet per minute) all into each 
 other, and divide by the pressure on each foot of sectional 
 area.* 
 
 The foregoing rules embrace only the pressure due to 
 friction, and not that due to the creation of velocity, so that 
 they may be regarded as being true of long pipes and air- 
 ways, as they are given, but as requiring an allowance for 
 the pressure due to the velocity in short pipes and air- ways. 
 This allowance renders the rules mush less simple. 
 
 Now these rules, which are found out by practical trials 
 or experiments, lead us to many very important conclusions 
 in reference to the best mode of conducting the ventilation 
 of mines ; in proof of which, it would be easy to multiply 
 examples. 
 
 These laws of friction may be illustrated by the follow- 
 ing examples : 
 
 In an air-way 10 feet square =100 feet area, and 
 25,000 feet, or nearly five miles long if the velocity of the 
 
 * If it is preferred to employ in these rules the velocity in feet per 
 minute, in lieu of in thousands of feet per minute, the co-efficient of 
 friction, in lieu of '26881 would become '00000026881; and if the 
 velocity is taken in feet per second it would become '000967716. 
 
40 
 
 air were 1 foot per second, or 60 feet per minute, the quan- 
 tity of air would be 6,000 feet per minute the pressure due 
 to friction (taking the pressure at 14- 7 Ibs. per square inch, 
 and the temperature at 32) would be '7812 Ibs. per square 
 foot of sectional area of the air-way, the horse power 
 being -142. 
 
 In another air-way of equal length, but instead of being 
 10 feet square only five feet square, giving only 25 feet, or 
 l-4th of the area of the larger air-way, we have the follow- 
 ing results : The rubbing surface in the small air- way would 
 only be one-half of that in the large one ; but, on the other 
 hand, the area to which the ventilating pressure would apply 
 would only be l-4th ; and at the same time the velocity of 
 an equal volume of air would be increased fourfold in the 
 lesser air- way, this increase of velocity alone making sixteen 
 times the friction, so that on the whole it would be thirty- 
 two times as great ; making the pressure on each square foot 
 2 4' 9 98 Ibs., being thirty- two times as great as in the large 
 air- way. And, therefore, on the whole the power expended 
 would, be also thirty-two times as great in the small as in 
 the large air-way, for the same amount of ventilation per 
 minute : the coals consumed would also be thirty-two 
 times as great. If furnace ventilation were used, and the 
 heat of the upcast shaft and pressure per foot were the 
 same, instead of 6,000 cubic feet per minute, as in the 
 large air-way, we should only have 1,061 feet in the smaller 
 one ; but in this case the coals burnt would only be 
 
 , or between l-5th and l-6th of the former quantity, 
 A/ 32 
 
 and the power would be less in the same proportion for 
 the lesser quantity of air. This shows in a striking manner 
 the great advantage of large air-ways. 
 
41 
 
 The calculations relative to the two cases, compared 
 with each other for the example just given, stand thus : 
 
 FOR THE LARGE AIR-WAY. 
 
 The length is 25,000 feet, and the perimeter of section 
 is 4 X 10 40 feet ; so that the robbing surface 
 
 s = 40 x 25000 = 1000000 square feet, 
 the area a = 10 x 10 = 100 square feet, 
 
 {\ 
 
 the velocity v = - = '06 in thousands of feet per min. 
 1000 
 
 and k = -26881, being the co-efficient of resistance 
 in feet of air-column of the 
 same density as the flowing air. 
 Now by formula (5) we have 7csv 2 
 
 P = 
 
 giving m this case a 
 
 _ -26881 x 1000000 x ('06 x -06) 
 
 P - "fooT~ = 9 6771( 
 
 feet of air-column as the pressure required. 
 
 Taking the flowing air to have had the density due to 
 a temperature of 32, and to a pressure of 14*7 Ibs. per 
 square inch, a cubic foot of it would weigh -080728 Ibs., 
 and, therefore, such a column would represent a pressure 
 
 9-67716 x -080728 = '7812 Ibs. per square foot ; 
 and hence the horse power due to the friction of 6,000 
 cubic feet of air per minute, in passing through uch an 
 air-way would be 
 
 6000 x '7812 
 
 = '142, or about l-7th of a horse power. 
 
 obOUO 
 
 FOR THE SMALL AIR- WAY. 
 
 Proceeding as in the former case, we have 
 26881 x (20 x 25000) x (-S4 x. -24) = 30 
 25 
 
42 
 
 feet of air-column, as the pressure required for putting the 
 same quantity of air, 6000 cubic feet per minute, into cir- 
 culation ; being equal to a pressure of 
 309-66912 x '080728 = 24'9989 Ibs. per sq. ft.; giving 
 
 6000 x 24-9989 
 
 33QQO % ' = 4-545 horse power. 
 
 If the pressure per square foot was the same in the small 
 as in the large air-way, or '7812 Ibs. per square foot, the 
 
 *7812 
 .air-column would be = 9-67716 feet high; and 
 
 the square of the velocity (in thousands of feet per minute) 
 would by formula (3) be 
 
 *.= __ 9 ' 67716 X 25 . =.0018 
 26881 X (20 x 25000) 
 
 and hence the simple velocity, in thousands of feet per 
 minute, would be 
 
 v = V 7 0018 = -042426 
 
 and the velocity in feet per minute would therefore be 
 
 042426 X 1000 = 42'426 ; 
 
 and this gives for the quantity of air that would be put 
 into circulation in the small air-way, by the same pressure 
 per foot that is required to circulate 6,000 cubic feet per 
 minute in the large one, 42-426 x 25 = 1,061 cubic feet 
 per minute, as has been stated. 
 
 To circulate 1,061 cubic feet of air per minute in the 
 small air-way would, however, only involve the applica- 
 
 tion of 
 
 1061 x -7812 
 
 A __, 
 
 =0251 horse power. 
 
 which, under the conditions of the small air-way, and the 
 assumed pressure, represents the entire power due to the 
 friction of the quantity of air that would circulate in it. 
 
48 
 
 Air, in being heated under a constant pressure, expands 
 l-459th part of its volume at the temperature of zero of 
 Fahrenheit's thermometer for each degree of temperature 
 imparted to it'; 459 cubic feet of air at become 469 at 
 10, 479 at 20, 489 at 30, and so on. 1,000 cubic feet 
 of air at 32, the temperature of melting ice, expand to 
 1,366^ cubic feet at 212, the temperature of boiling water. 
 To find the relative volumes occupied by equal weights of 
 air, under equal pressures, but at different temperatures, 
 we have simply to add the constant number 459 to the 
 temperatures, and the sums give the relative volumes. The 
 ordinary pressure of the atmosphere is equal to that of a 
 column of water about 34 feet or 400 inches in height ; we, 
 however, seldom employ a difference of more than 2 or 3 
 inches of water column, as ventilating pressure in mines. 
 The pressure of the air is about 2,116 Ibs. per square foot, 
 but we seldom employ more than 10 to 17 Ibs. extra as 
 ventilating pressure. Owing to the ventilating pressures 
 being so small, the changes of density in the air of mines 
 (as it circulates), arising from changes of temperature, the 
 mixture of watery vapour or steam, the gases given off, 
 and one or two other causes, give rise to small local pressures 
 in the various splits of air in a mine. In rise splits these 
 local pressures usually operate against the general venti- 
 lating pressure, and lessen the quantity of air that would 
 otherwise circulate. In dip splits these small local pressures 
 commonly act in the same direction as the general ventila- 
 ting pressures, and so add to the amount of their ventila- 
 tion. This arises from the return air of any split being 
 generally less dense than the intake air. 
 
 The laws of ventilation lead us to conclude that if we 
 increase or decrease the total ventilating pressure, and total 
 
44 
 
 quantity of air circulating in a given time, where the seam 
 of coal is perfectly level, each way or split will get & fixed 
 share of the whole of the air entering the mine, no matter 
 how long or short may be the different splits, and no 
 matter how great or small may be the quantity of air. This 
 is contrary to an old notion, that a short split gets an in- 
 creasing, and a long one a decreasing share of any lessened 
 amount of ventilation, apart from considerations as to the 
 rise or dip of the seam. Not long ago this point was severely 
 tested, by numerous experiments, at several collieries ; the 
 results showed that the old idea was a mistaken one, and that 
 the only changes that took place in the proportion or share of 
 air going to different splits, with a reduced ventilation, arose 
 from their relative rise or dip, together with the relative den- 
 sities of the intakes and returns, and had no connection with 
 the mere lengths of the splits. In ordinary cases, where the 
 air of the returns is less dense than that of the intakes, if 
 we have a short level split regulated so that, with the full 
 ventilating pressure, it gets the same amount of air as a 
 long dip split ; and if. we then halve the total quantity of 
 air circulating, we find that the short level split no longer 
 gets its share, but only a quantity less than that which 
 goes into the long dip split ; the very reverse of this is the 
 case where the long split is a rise one ; and these results 
 are perfectly agreeable to the laws of ventilation that have 
 been stated. In practice, and with the ordinary splits of 
 air used in mines, except in extreme conditions as to the 
 amount of rise and dip, and changes of density in the air, 
 and in the amount of ventilation, the share or proportion 
 of air going into the different splits of a mine is nearly 
 maintained, whether we increase or lessen the total amount 
 of ventilation ; and any deviation from this depends upon 
 
45 
 
 the rise or dip of the splits, and not at all upon their 
 relative lengths. In practice, then, when any reduction of 
 ventilation has been brought about, we should generally 
 find that the rise splits have been more affected than dip 
 ones, if even the rise splits are shorter than the dip ones, 
 and we should therefore expect to find- accumulation of gas 
 in the short rise splits rather than in the long dip splits of 
 the mine. The greater the rise the greater is the danger 
 of this, quite apart from the mere length of the splits, 
 supposing them to be equally well ventilated to begin with. 
 So far as experiments have gone, they show that if we 
 had a series of equal sized and similarly shaped air-ways, 
 made of different substances, the friction of air in passing 
 through them would differ according to the nature of the 
 substances. 
 
 Taking the friction in earthenware pipes at 100 
 
 In the air- ways of mines it would also be 100 
 
 In sheet-iron pipes, new and clean 39 
 
 In do. rusty inside 10 
 
 In cast-iron pipes, sooty inside 20 
 
 In do. tarred inside 18 
 
 In tin pipes the friction would only be 10 
 
 So that 1-1 Oth of the pressure would send the same 
 quantity of air through a tin pipe that would be required 
 to force that quantity of air through an earthenware pipe 
 of the same size in the same time. (See Table annexed.) 
 
 From these laws we learn, that the quantity of air 
 that will pass through any mine is greater or less as the 
 ventilating pressure is greater or less, but not in the same 
 proportion. "When the air-ways are the same, the quantity 
 of air only alters in the proportion of the square root of 
 
 D 
 
46 
 
 the pressure ; so that a fourfold pressure only gives a 
 double quantity of air, and a ninefold pressure only gives 
 a treble quantity of air. But, on the other hand, one-fourth 
 
 TABLE. 
 
 Showing the values of the co-efficient of friction, represented by the 
 letter k, in the formulae given at page 39, being the height in feet 
 of air column of the same density as the flowing air, required to 
 overcome the frictional resistance encountered by 1,000 cubic feet 
 of air per minute in passing through a passage having one foo of 
 sectional area, and presenting one square foot of rubbing surface 
 to the air in motion. 
 
 Nature of the 
 material composing the 
 pipe or air-way. 
 
 State of the 
 internal or 
 rubbing surface 
 exposed 
 to the wind. 
 
 Observers' names 
 
 General 
 Temperature of 
 the air or gas. 
 
 Head of column 
 of the same den- 
 sity as the moving 
 air or gas re- 
 quired to over- 
 come the friction, 
 being the co- 
 efficient of 
 friction t= K. 
 
 Burnt earth 
 Galleries of a coal-mine 
 
 Sheet iron 
 Cast iron ? 
 Cast iron 
 Cast iron 
 Gas in pipes cast iron 
 Water in pipes do. 
 Sheet iron 
 Tinned iron 
 
 Clean 
 Ordinary state 
 
 New and clean 
 Ordinary ? 
 Sooty 
 Old, Tarred 
 Ordinary 
 Ordinary 
 Old and rusty 
 
 Pe"clet 
 G. C. Greenwell 
 Peclet 
 / Mons. Rudler 
 I Peclet 
 Girard 
 Mr. Hawkesley 
 Eytelwein 
 Girard 
 D'Aubuisson 
 
 Hot 
 Cool 
 
 Hot! 
 
 Hot 
 Hot 
 Cool 
 Cool 
 Cool 
 Cool 
 Cool 
 
 0-26881 
 0-25436 
 From 0-10583 
 to 0-06773 
 0-08466 
 0'05292 
 0-04844 
 0-03014 
 0-03028 
 G'02752 
 0-02540 
 
 REMAKKS. In applying these values of k to the formulae at page 39 since 
 they are calculated for velocities of which the unit is 1,000 feet per minute, the 
 real velocities in feet per minute must be divided by 1,000, to give the value of v 
 in the formulae ; and v in the formulae must be multiplied by 1,000 to give the 
 velocity in feet per minute. 
 
 of the pressure still gives one-half of the air, and one- 
 ninth of the pressure gives one-third of the air. The 
 changes in the quantity of air, then are sluggish as com- 
 pared with the changes in the ventilating pressure, only 
 varying as its square root. The quantity of air, however, 
 is more sluggish still in reference to the power employed 
 to cause it to circulate. The quantity of air only varies 
 
47 
 
 as the cube root of the power, and of the quantity of coals 
 burnt to produce it ; so that eight times the coals only 
 double, and twenty-seven times the coals only treble the 
 quantity of air circulating in a mine, whether the ventila- 
 tion is produced by furnace-action, ventilating machines, 
 or otherwise, so long as the air-ways remain in the same 
 unaltered state. From this we learn, that we must not ex- 
 pect any great general improvement in the ventilation of 
 mines from a mere increase of power ; any increase in the 
 quantity of air in the same air-ways is slow, small, and 
 costly, compared with the necessary increase of power re- 
 quired to produce it. 
 
 In the same manner these general laws show us, that 
 the quantity of air increases as we decrease or lessen the 
 extent of the frictional rubbing surface ; but again, not in 
 the same proportion, but only as the square root of the ex- 
 tent of the rubbing surface. If we could do away with 
 three-parts out of four of the rubbing surface, so as to re- 
 duce it to one-fourth, other things being the same, we should 
 only double the quantity of air in the mine ; if the rubbing 
 surface were reduced to even one-ninth, the quantity of air 
 circulating per minute would only be increased to three 
 times its previous amount. On the other hand, if the ex- 
 tent of workings and rubbing surface were increased to four 
 times, or nine times their previous amount, while the area 
 of the air-ways and the ventilating pressure remained unal- 
 tered, the air would only be lessened to one-half or one-third 
 of its previous amounts respectively by such extensions, if we 
 suppose the size of the air-ways and the number of splits of 
 of air to remain the same, as well as the ventilating pressure, 
 in each case. 
 
 From these laws, then, we learn, that either to increase 
 
48 
 
 the ventilating pressure, or to lessen the extent of rubbing 
 surface exposed to the air circulating in mines, is a very 
 slow and very costly mode of proceeding to increase the 
 amount of ventilation, as the quantity of air circulating 
 in a given time alters so slowly with any alteration that 
 may be made in the ventilating power or pressure, or in the 
 mere extent of rubbing surfaces that may be presented to 
 it. For general improvements we must, therefore, look 
 chiefly in some other direction, owing to these being slow 
 and costly modes of increasing the ventilation of a mine. 
 
 The same general laws of resistance show us that if we 
 could reduce the velocity of the air, consistently with 
 increasing the quantity circulating in a minute, we should 
 greatly lessen the friction in comparison with the quantity 
 of air circulating, and so obtain an increased quantity for 
 the same amount of friction, or by the same ventilating 
 pressure. This object is accomplished by splitting the air, 
 so that instead of allowing the whole of the air to traverse 
 the whole of the workings, a separate portion is taken into 
 each different district of workings, and also brought out 
 in a separate channel to a point near the upcast shaft, after 
 it has done its work. The air, as a whole, thus has as many 
 ways to go in, and as many to come out by, as there are 
 separate splits in the mine ; the extent of the rubbing 
 surface is not lessened by this, on the whole, but the area 
 offered to the air is greatly multiplied ; and although the 
 velocity of each current may be reduced, still, on the whole, 
 the quantity of air in all the splits is very much greater 
 than if there were only one single current in the mine, even 
 when the ventilating pressure is the same. Splitting the 
 air does not necessarily enlarge the area offered to the air 
 in the shafts, and the increased resistance arising from the 
 
49 
 
 increased quantity and velocity of air in them sets a limit 
 to the benefits resulting from splitting the air in a mine. 
 Owing to the resistance offered by the shafts, we dare not 
 have more than a limited number of splits in a mine, 
 because although every split adds to the total quantity of 
 air circulating, still in each separate split the quantity ulti- 
 mately becomes less and less, and if the number be too 
 great, the current of each becomes too feeble and slow to 
 sweep into the holes, corners, and places driven in advance 
 of the actual current ; and besides this, powder smoke is a 
 long time in being carried away from the workmen. Still 
 it is a fact that an additional quantity of air, on the whole, 
 is obtained from every new split that is made. 
 
 The following general rules should be observed in 
 splitting the air in mines : 
 
 Every principal split of air should commence as near as 
 possible to the bottom of the downcast shaft, and should 
 have a distinct air-way to return in, as nearly as may be, 
 to the furnace or the bottom of the upcast, shaft, except in 
 cases where it is necessary to mix different currents, lest 
 some one or more of them may be dangerously charged with 
 gas. Splits of air only commencing far into the workings 
 of a mine have comparatively little effect in increasing the 
 quantity of air. 
 
 Where the air- ways are nearly of the same area in all 
 parts of a mine, and the gases given off, and the workmen 
 employed are pretty evenly distributed, the length of the 
 runs of the different splits should be as nearly equal to 
 each other as circumstances may permit. The observance 
 of this rule has a tendency to render regulators and other 
 obstructions comparatively needless, and so to increase the 
 amount of ventilation. 
 
50 
 
 If we have a number of splits of air in a mine, each 
 with an equal amount of air, then it is necessary so to 
 obstruct each of the shorter splits as to cause their frictional 
 resistances, when they have their proper share of air, to be 
 as great as that of the very longest split, when it also has 
 its due share ; otherwise they would get too much air, and 
 the longer ones too little. These obstructions, of course, 
 lessen the total quantity of air circulating. 
 
 The increased quantity of air obtained by splitting de- 
 pends greatly upon the relative depths and areas of the 
 shafts, as compared with the lengths and areas of the 
 air- ways forming the workings of the mine. Supposing a 
 mine to have such shafts and air-ways, that when there are 
 five equal splits of air, the shaft resistances amount to 
 one-half of the resistances offered by the mine and this is 
 no uncommon case then, if before splitting the air at all, 
 we had a ventilation of 10,000 cubic feet of air per minute, 
 the following are the quantities of air that would circulate 
 by increasing the number of equal splits, while the entire 
 extent of the workings, and the upcast shaft, and the 
 ventilating pressure all remained the same : 
 
 No. of 
 Currents. 
 
 Quantities of Air 
 on the whole. 
 
 Quantities in each 
 split. 
 
 1 
 
 10000 
 
 10000 
 
 2 
 
 27892 
 
 13946 
 
 3 
 
 49449 
 
 16480 
 
 4 
 
 71527 
 
 17882 
 
 5 
 
 90789 
 
 18158 
 
 6 
 
 107800 
 
 17966 
 
 10 
 
 141710 
 
 14171 
 
 In this case, the coals burnt, whether in a furnace or 
 by an engine driving a ventilating machine, would increase 
 
51 
 
 in the same proportion that the quantity of air increased, 
 because the power would increase in that ratio. If the 
 coals burnt, and the power remained unaltered, the results 
 would only be as below : 
 
 No. of 
 Currents. 
 
 Total Quantities 
 of Air per minute. 
 
 Quantities of Air 
 per minute in each 
 split. 
 
 1 
 
 10000 
 
 10000 
 
 2 
 
 19813 
 
 9906 
 
 3 
 
 29022 
 
 9674 
 
 4 
 
 37121 
 
 9280 
 
 5 
 
 43736 
 
 8747 
 
 6 
 
 48797 
 
 8133 
 
 10 
 
 58556 
 
 5856 
 
 Enlarging the sectional area or size of air-ways has a 
 great effect in increasing the ventilation, but it is attended 
 with great cost, and in general terms may be said to be 
 much less effectual than judiciously splitting the air into a 
 series of different currents. The beneficial effects of split- 
 ting air are, I believe, more fully appreciated, and the 
 practice is more extensively followed in the Newcastle 
 coal-field than in any other mining district; but, even 
 there it too often happens that the splits are made too far 
 from the bottom of the downcast shaft, and are again 
 brought into the same return too soon after they leave the 
 face of the workings. This often arises from pillars being 
 worked away near the shafts, without proper places being 
 left to make additional air-ways leading to and from the 
 more distant parts of the mine. This is a very common 
 oversight, and often entails either danger or a serious 
 outlay, which might be avoided by care and forethought. 
 
 ON THE MEANS OF APPLYING POWER OR PRESSURE 
 TO PRODUCE VENTILATION. 
 
 We have seen that pressure is required to put air into 
 
52 
 
 / 
 
 motion, and, more particularly, to overcome the friction 
 it meets with in rubbing against the top, bottom, and 
 sides of the galleries in mines. We have next to consider 
 the means employed to give rise to this ventilating pressure. 
 There is constantly a pressure of nearly a ton to the square 
 foot in every direction in the air near the surface of the 
 earth, owing to the weight of the air above it ; and we must 
 either increase or lessen the amount of this pressure, in 
 order to put the air into motion; and it is only the amount 
 of this increase or decrease, and not the entire pressure, 
 that puts the air into motion and overcomes the friction 
 in mines. 
 
 A B Take the case of two pits or shafts, 
 
 of equal depth, and having their tops 
 and bottoms on the same level, and 
 filled with stagnant air, which like- 
 wise occupies an opening, extending 
 from the bottom of one shaft to the 
 
 bottom of the other ; and suppose that, in the first place, 
 the weight of the air in one shaft is the same as that in the 
 other, the temperature and other conditions being the same 
 in each, and that the shafts are of the same sectional area 
 or size: in this state the two columns of air exactly coun- 
 terbalance and support each other, so that there is no motion 
 in the air, and therefore no ventilation is produced ; nay, 
 further, if one shaft be ever so much larger than the other, 
 the air it contains can only press upon that in the smaller 
 one over the area of the smaller section ; the air contained 
 in the extra size of the larger shaft resting pr pressing upon 
 the sides of the shaft or air- way at the place where the area 
 is lessened, and not upon the air in the smaller shaft ; so 
 that whatever may be the relative sizes of the shafts, the 
 
53 
 
 air in the one will balance that in the other if the density 
 of the air is the same in each ; this may be termed the 
 pneumatic paradox. If, however, by means of a furnace, 
 at F in the- diagram, the air in one shaft is heated and 
 expanded, it becomes lighter, bulk for bulk, than the cool 
 air in the other, and no longer balances it ; the pressure of 
 the heavier air then overcomes that of the lighter air, and 
 pushes it up the shaft before it, while the cool air from the 
 cool shaft takes its place, but not in a cool state, as it gets 
 heated in its turn in passing over the furnace, so that there 
 is a continual current of cool air going down one shaft 
 which pushes before it a constant current of hot air up the 
 other shaft. 
 
 In mines the air, instead of being allowed to go direct 
 from the bottom of one shaft to the furnace and up the 
 other, is guided by means of stoppings and doors into and 
 along the various passages forming the workings of the 
 mine, before it is brought upon the furnace or into the 
 upcast shaft, and, by this means, a continual stream of air 
 is made to sweep through the workings and mix with and 
 carry on the gases as they are given off, and this is called 
 the ventilation of the mine. 
 
 In some cases, men, boys, and horses require to travel 
 in directions that the air is not wanted to go, and in such 
 cases we cannot build up the way by a stopping, but have 
 to place doors to stop the passage of the air ; in many cases, 
 the opening of a door to allow a person or horse to pass 
 would have a bad effect by allowing the air to pass through 
 it even for so short a time, and to avoid this evil two doors 
 are employed, so that one may always be closed w r hen the 
 other is open. The use of doors in the principal roads of 
 mines is objectionable where it can be avoided, and is much 
 
54 
 
 less common, at least in some districts, than formerly ; in 
 other districts of the kingdom the number of ventilating 
 doors is very great, notwithstanding the danger and cost 
 attending their use. The neglect of keeping doors shut 
 has, no doubt, often led to serious explosions of gas in 
 mines. In some cases it is necessary that the route of one 
 split or current of air should intersect and cross that of 
 another, and in such cases one current is carried over or 
 under the other by means of drifts or masonry to prevent 
 their coming into contact with each other ; this arrangement 
 is called an air-crossing or bridge. When an explosion 
 occurs, the force of the concussion often destroys air- 
 crossings, and thereby interrupts the ventilation ; so that 
 they should be avoided as far as possible, and made very 
 strong where they are used in fiery mines. 
 
 It has already been stated that, where there are several 
 splits of air in a mine, of different lengths, and offering 
 different resistances, we sometimes find that too little air 
 goes into the longer splits, compared with the quantity 
 going into the shorter ones ; and, in order to correct this 
 evil, we put regulators or contractors into the shorter ones 
 so as to increase the natural resistance they offer, and cause 
 more air to go into the long splits. Regulators, although 
 useful where they are unavoidable, are not desirable, as they 
 contract the air- ways, and so lessen the total quantity of 
 air circulating in the mine in a given time. As far as may 
 be, the routes of the air should be so proportioned that 
 each split may obtain its proper share of air without using 
 any artificial regulators. Doors, air- crossings, and regula- 
 tors should be avoided in all cases where the circumstances 
 of the mine admit of it. 
 
 In order to find the amount of ventilating pressure, 
 
55 
 
 and the power arising from the use of a ventilating 
 furnace, we require to know the weight of a cubic foot of 
 air at different temperatures and under different pressures. 
 Careful experiments show that 459 cubic feet of air at 0, 
 or zero of Fahrenheit, the common thermometer, weigh 
 39'76 Ibs., when the pressure is 30 inches of mercury of 
 the density due to 32 a pressure equal to nearly 14f Ibs. 
 per square inch, which is the ordinary pressure of the 
 atmosphere but it only weighs l-30th of this, or 1*3253 
 Ibs. when the pressure is only 1 inch of mercury ; and 
 since 450 feet of air at expand exactly a cubic foot for 
 each degree of heat added, we get the following rule to find 
 the weight of a cubic foot of air, at any temperature, and 
 under any pressure : 
 
 w 1'3253 x I 
 459 + t 
 
 Where I = the height in inches indicated by the barometer, 
 and t = the temperature by Fahrenheit's thermometer. 
 At 38, under a pressure of 30 inches of mercury, 100 cubic 
 feet of air weighs just 8 Ibs. ; a box 5 feet every way 
 would just contain 10 Ibs. of such air. 
 
 On one occasion, at Hetton Colliery, when 225,176 
 cubic feet of air per minute were circulating, the average 
 temperature of the air in the downcast shaft was 43^, and 
 that of the air in the upcast shaft was 211. Now, by the 
 rule given (if we take the barometer half-way down the 
 shaft to have shown a pressure of 30J inches of mercury), 
 the weight of a cubic foot of air, taking the average, in the 
 downcast shaft, would be '08044 Ibs. ; and the pit being 
 900 feet deep, this air would produce a pressure of -08044 
 x 900 = 72' 39 6 Ibs. on each square foot by its mere 
 weight. The air in the upcast shaft, owing to its' being 
 
56 
 
 hotter, would be lighter, and only produce a pressure on 
 each foot = 54/297 Ibs ; and hence the difference of pressure 
 on each square foot of area, between the two columns of air, 
 would be = 18'099 Ibs. Now, in order to find the horse 
 power producing ventilation, we require to multiply this 
 difference of pressure of 18*099 Ibs. on the square foot, by 
 the number of cubic feet of air circulating per minute, and 
 then to divide the result by 33,000, the number of Jbs. raised 
 one foot high per minute by a horse power. In this case, 
 then, we find the ventilating power at Hetton Colliery must 
 have been 
 
 Ibs. c. ft. pr, min. 
 
 18-099 x 225,176 
 -8*660- " 
 
 225,176 cubic feet of air per minute being in circulation 
 at the time. Some part of the extra heat of the air in the 
 upcast over that in the downcast shaft, would have arisen 
 from the heat of the mine, and would have caused what 
 is called a natural ventilation, even if furnaces had not been 
 used. But natural ventilation is generally very small in 
 amount, and cannot be depended upon, as, in hot weather, 
 the downcast column of air is little or no cooler or denser 
 than the air in the upcast, and, by making the weight or 
 pressure of the two air columns equal there is a liability to 
 stop all ventilation. 
 
 Where furnaces are used to produce ventilation, the 
 deeper the upcast shaft the better ; because this gives rise 
 to a longer upright column of hot air, and so causes a 
 greater ventilating pressure, and consequently a brisker 
 ventilation. Furnaces are not well suited for causing ven- 
 tilation in shallow pits for this reason ; and sometimes 
 machines are fixed at the top of the pit to pump the air 
 
57 
 
 through the mine. These machines, for the most part, 
 exhaust air out of the upcast shaft, and the pressure of the 
 denser air in the other, or downcast shaft, causes the current. 
 Such a ventilating machine, like a furnace, acts by rendering 
 the upcast column of air lighter, bulk for bulk, than the air 
 in the downcast shaft ; the same effect is sometimes pro- 
 duced by large fans, the machines mostly being worked by 
 steam engines. A few of these ventilating machines are 
 used in the south of England and in "Wales, and a great 
 number are used on the Continent. Ventilating machines 
 of the best construction consume less coals (to produce the 
 same quantity of ventilation) than furnaces, except in very 
 deep and dry shafts. But coals are plentiful at collieries, 
 and the liability of ventilation being suspended by the 
 breakage of the machinery, and the inconveniences attend- 
 ing the stopping of the ventilating machine for repairs to 
 itself or the engine, together with the difficulty of applying 
 ventilating machines to working shafts, render them, in 
 the opinion of many persons, less to be depended upon than 
 furnaces in general. Taking the average of eleven different 
 collieries in the Newcastle district, each pound of coal puts 
 13,000 feet of air into circulation by the action of furnaces. 
 In some collieries two or three times as much air is circu- 
 lated, by each pound of coal, as in others, depending on 
 the depth of shaft, and its state as to dryness or wetness, 
 and on the friction of the air in the shafts and in the mine 
 itself. There are in Wales some seven or eight ventilating 
 machines at work, producing ventilations varying from 
 1 6,000 to 75,000 cubic feet of air per minute. The largest 
 machine is one recently erected at Deep Duffiyn Collieiy, 
 which, with air-ways of sufficient area, is capable of pro- 
 ducing a ventilation of double the latter quantity. 
 
58 
 
 Jets of steam were proposed to produce the circulation 
 of air in mines a few years ago, but by an elaborate series 
 of experiments their effects were found to be far below that 
 of furnaces, and the cost to be very great ; the idea of their 
 utility for ventilating mines was therefore abandoned. The 
 useful work contained in a jet of steam, probably varies as 
 the cube of the velocity of the steam, so that if the same 
 quantity of water was converted into steam, in a given 
 time, the power contained in it would depend upon the 
 smallness of the jet orifice it had to escape through ; by 
 halving the area of the jets we should obtain eight times 
 the power, and should therefore get a double quantity of 
 air through the same mine ; by reducing the area of the jets 
 to one-third, we should obtain a treble quantity of air, by 
 the same quantity of steam, in a given time. At least 
 these are the results given by calculations, made upon the 
 principles of mechanics, which are found to be true for 
 streams of water and air. I have not taken pains to com- 
 pare them with the results of the experiments on steam jets 
 as applied to ventilation, because the results seemed to hold 
 out no hope of steam jets ever been made available for 
 ordinary ventilation. There are, no doubt, temporary and 
 peculiar circumstances under which steam jets may be useful 
 in the production of ventilation, such as cases where it is 
 either unsafe or impracticable to use ordinary furnace action. 
 
 Falls of water are sometimes employed in downcast 
 shafts to cause a current of air to descend ; but, as the water 
 has, for the most part, to be raised again from the mine, 
 and as the effects they produce are small, in proportion to 
 the power employed, this mode of ventilation is seldom used, 
 except where furnace action or other means are necessarily 
 excluded. 
 
59 
 
 ON THE INSTRUMENTS USED IN CONNECTION WITH 
 THE VENTILATION OF MINES. 
 
 Barometer. The pressure of the atmosphere, in different 
 states of the weather, varies from 28^ to 31 inches of mer- 
 curial column, being from 2,016 to 2,192 Ibs. per square 
 foot ; and it is found that the natural discharge of gas in 
 mines becomes greater as this pressure becomes less, so that 
 the reduced atmospheric pressure as shown by a barometer, 
 is a warning that an increased quantity of gas may be ex- 
 pected to be given off in mines, and, therefore, calls for in- 
 creased care and vigilance to keep the ventilation at its 
 greatest point, and for taking precautions against the enemy. 
 The air pent up in goaves, and abandoned excavations, also 
 expands in volume from the reduction of pressures which 
 causes the fall of the barometer; the increased volume being 
 given out into the air-ways, and often being mixed with 
 gases necessitating careful attention,. as the barometrical 
 pressure of the atmosphere is lessened ; the more suddenly 
 the pressure falls the more observable are these results. A 
 very sudden fall of the mercury is accompanied by a worse 
 effect on mines than a greater fall, provided it takes place 
 less rapidly. An increase or decrease of the pressure of the 
 atmosphere has little or no effect in altering the volume of 
 air passing through a mine in a given time, although it 
 alters the density and weight of such air often to a consider- 
 able extent. 
 
 A good portable barometer may be used to ascertain the 
 friction of air in passing along air-ways, because the loss of 
 pressure, by friction, as the air circulates, is always taken 
 off the pressure of the air itself ; so that in level air- ways 
 the air is less and less compressed as we proceed in the di- 
 rection followed by the air, and the reduction of pressure 
 
60 
 
 is an exact measure, in such air- ways, of the pressure spent 
 on friction. When the air-way rises or dips, allowances for 
 this have to be made in finding the amount of friction from 
 the pressure of air in this manner. Aneroid barometers ap- 
 pear to be better suited for use in mines than the common 
 barometer or weather glass, as they are more portable, less 
 liable to derangements, and almost equally reliable, at least 
 for comparative indications, which are just as useful as ab- 
 solute ones in mines. 
 
 Thermometer. The thermometer is used to measure the 
 heat of air in mines; when the fresh air, going down a down- 
 cast shaft, is heated, it expands and becomes lighter, and is, 
 therefore, less able to force the air before it through the 
 the mine ; in other words, by being heated, the weight of 
 the column of air in the downcast shaft is reduced till it is 
 more nearly equal to that in the upcast shaft, and, con- 
 sequently, the ventilatmg pressure is lessened, and, there- 
 fore, the quantity of air circulating is also reduced in 
 amount. By the use of this instrument we find the differ- 
 ence of temperature between the air in the downcast and 
 that in the upcast shaft, and so are able to calculate the 
 ventilating pressure due to the action of a furnace. 
 
 Water Gauge. The water gauge is merely a glass tube, 
 bent into the form of the letter U with a scale of inches 
 and parts, by which we can measure the difference between 
 the height of the water in one tube and that in the other. 
 It has already been stated that the air loses the pressure that 
 is spent on the friction as it progresses along an air-way. 
 Now, when an air-way happens to turn so as to come nearly 
 parallel to itself, there is often a door or stopping separating 
 the two adjacent parts of the same air- way, and this instru- 
 ment enables us, in a direct way, to measure the amount of 
 
61 
 
 pressure that is spent on friction between the two adjoining 
 parts of the air-way so situated. The air has less pressure 
 on the outcome or return side of the separation than the 
 air on the intake side, which has not yet met with the fric- 
 tion of the intervening distance of air-way. If the water 
 in one leg of the tube is exposed to the pressure of the in- 
 take air, while that in the other is exposed to the lesser pres- 
 sure of the return air, the greater pressure on the intake leg 
 of the water gauge sinks or depresses the surface of the water 
 in that leg, and raises it in the other leg ; the difierance of 
 level, which represents the ventilating pressure spent on the 
 air- ways lying beyond the place where it is taken, is seldom 
 so much as three inches, and often only one inch in well- 
 ventilated mines. The amount of water gauge can be in- 
 creased, either by increasing the ventilating pressure, and, 
 consequently, also the quantity of air circulating in a given 
 time, while the air-ways are in the same state, or it can be 
 increased by falls of material, or other obstructions in the 
 air- ways, even while they lessen the quantity of air circu- 
 lating ; because such obstructions increase the frictional re- 
 sistance of the air, and the gauge is a measure of that resist- 
 ance. A water gauge does not show the shaft resistance 
 when used in a mine ; the pressure shown by the water 
 gauge is equal to the general shaft ventilating pressure, less 
 or minus the friction due to the air in the shafts and in the 
 air- ways extending from the shafts to where the gauge is 
 tried. It is also a measure of the resistances the air meets 
 with in the workings lying beyond it, less or minus any 
 local force, arising from the air in the returns being 
 lighter than that in the intakes, in dip-ways; or it is 
 equal to such friction added to any such pressure that may 
 
 E 
 
operate against ventilation from the same cause in the 
 rise-ways or splits of air in the mine ; and in cases where 
 the air of the returns is more dense than that of the in- 
 takes, the effects arising from the dip or rise of the work- 
 ings will, of course, operate in the reverse manner upon 
 the indications of the gauge. When the air- ways remain 
 in the same state, the amount of water gauge increases as 
 the ventilation increases, and falls as it decreases; but 
 the proportion of variation of the gauge-pressure is much 
 greater than that of the quantity of air circulating; the 
 square of the quantity of air, except in so far as local pres- 
 sure may interfere, is proportional to the pressure indicated 
 by the gauge, because the friction varies as the square of the 
 quantity of air. 
 
 The Anemometer is an instrument used to measure the 
 rate at which the air flies in mines. That invented by the 
 late Mr. Biram is the one mostly used in English mines ; 
 it is not a very easy matter to find how much each of these 
 instruments requires to be allowed for its own working 
 friction ; no perfect rule has yet been established for this 
 purpose, although one is much needed. An approximate 
 rule requires that a constant quantity should be added to 
 the number of revolutions in a minute, no matter what may 
 be the speed of the wind or of the instrument ; and that 
 the sum so obtained should be multiplied by another con- 
 stant quantity, to give the velocity of the air in any terms 
 in which we wish to find it. Coombes' anemometer can be 
 put into or out of gear by pulling strings attached to it ; 
 this instrument is said to give very correct results, and is 
 greatly used on the Continent ; it is, however, more trouble- 
 some to use than Biram's anemometer, and is seldom seen 
 
63 
 
 in our mines. There are a few other kinds of anemometers ; 
 but a good and simple instrument, or mode for finding the 
 velocity of air in motion, has probably yet to be contrived. 
 The Hygrometer. In fine experiments, the hygrometer 
 is used to ascertain the proportion of moisture in the at- 
 mosphere of mines, from whence its density and also its 
 capacity for heat are found. Mason's wet and dry bulb 
 hygrometer is better adapted for use in mines than the 
 more delicate one of Daniel. The return air in nearly all 
 mines is found to be saturated with vapour of water ; that 
 is to say, it contains the greatest quantity of vapour that 
 can exist in it at its temperature ; and a portion of vapour 
 is condensed by the least degree of cooling that takes place 
 in the air. An atmosphere saturated with vapour is lighter, 
 bulk for bulk, than another at the same pressure and tem- 
 perature, but containing less vapour. 
 
 In the discussion which followed 
 
 Mr. ATKINSON said : Supposing you have a long split 
 and a short one in the same mine, and you regulate or con- 
 tract the short one by an artificial obstruction until the 
 quantity going into each is equal; then supposing, from some 
 cause or other, the general ventilating pressure is gradually 
 reduced, what would be the result ? Would the short split 
 get half the remaining total quantity of air, or would it get 
 less or more ? That question would have been answered in 
 my younger days by saying that the short split would 
 ultimately take the whole of the air, and none would go to 
 the long one. Now, however, it is a fact, which I have 
 
64 
 
 proved over and over again, that if the air-ways are level, 
 and you reduce the ventilating pressure, each split will take 
 its original proportion; but if the long one is a dip-way and 
 the short-way is a level one, on reducing the gross quantity 
 of ventilation the long- way gets more than its original share 
 of the reduced quantity, and so takes the lead of the short 
 split. If, on the other hand, the long split is a rise and the 
 short a level, on reducing the gross quantity the long split 
 gets less and the short one gets more than its share. Sup- 
 posing one split gets 60 per cent, and the other 40 per cent, 
 of the total to begin with, if the air-ways are level, each will 
 get the same percentage when the gross amount is lessened. 
 Just the reverse results take place if you take the propor- 
 tions from any standard amount of ventilation, and then 
 increase the gross quantity, where there are rise and dip 
 splits, supposing the air in the returns to be hotter and less 
 dense than in the intakes in each case. If, however, the re- 
 turns were so mixed with carbonic acid gas, and so cool as 
 to be more dense than the air in the intakes, then the re- 
 verse results would ensue on increasing or reducing the 
 ventilating pressure where the splits are not level. We had 
 a long discussion about this at the North of England Insti- 
 tute of Mining Engineers. Some one suggested, after the 
 Lundhill accident, that instead of having air kept so much 
 in one current, if they had taken it up each bank on separate 
 splits, they would have got a much better ventilation ; but 
 the objection was raised that in the event of the furnaces 
 being low and the general ventilation being reduced, the 
 far-off places would get no air ; it would all run through the 
 "short cuts ;" and it was to correct that idea that the mat- 
 ter was made the subject of investigation by careful experi- 
 
65 
 
 ments. Further, the benefit of splitting air depends in a 
 great measure upon the proportion of resistance that occurs 
 in the shafts as compared with that which occurs in the 
 workings. The total pressure applied may be divided into 
 two separate items, one of which is employed to overcome 
 the shaft friction, and the other to overcome the resistance 
 in the workings. Generally speaking, you can subdivide 
 the workings till you reduce the friction very materially ; 
 but the friction in the shaft is, of course, always the same 
 for a given quantity of air, and it. is only from reducing the 
 friction in the workings that the beneficial results of split- 
 ting the' air are derived. As to dumb drifts in some_col- 
 lieries, where discharges of gas occur, it might be expedient 
 to use them ; but he would rather have a sweeping venti- 
 lation, as a rule, and a mixing of the return air from the 
 place where the gas was given off with that from the other 
 ways, so as to render it safe before reaching the furnace. 
 If you supply the furnace with fresh air, you never get with 
 the same furnace the same amount of air into the workings, 
 and our object is to cut down the amount of friction in the 
 downcast and upcast shafts. There is one rare case where 
 that does not hold, and that is if your returns were so 
 charged with carbonic acid gas, so fearfully charged with 
 it, that they would not let the furnace burn, you would have 
 nothing else for it but to use fresh air, but you would use 
 it at the expense of not getting the same amount of venti- 
 lation as you would get with ordinary air. 
 
PUBLIC COMPANIES. 
 
 flfcemoranbums 
 
 AND 
 
 Hrticles of Hssociatioru 
 
 Share Certificates, Cheque, Receipt, 
 
 AND 
 
 Common Seal Books, 
 
 (probuceb in f#e QSesf JSfgfe, on ]E)anb*mabe or 
 
 e preferreb. 
 
 BS AND DESIGNS 
 
 OF ANY OF THESE FORMS CAN BE HAD ON APPLICATION.^ 
 
 ANDREW REID, 
 
 GNGI^&YEI^ AND IIIJIIHOGI^APHEI^ 
 printing Court JBuilMngs, & \2, Collingwoofc St f 
 
 New castle-up on- Tyne. 
 
UNIVERSITY OF CALIFORNIA LIBRARY, 
 BERKELEY 
 
 THIS BOOK IS DUE ON THE LAST DATE 
 STAMPED BELOW 
 
 Books not returned on time are subject to a fine of 
 50c per volume after the third day overdue, increasing 
 to $1.00 per volume after the sixth day. Books not in 
 demand may be renewed if application is made before 
 expiration of loan period. 
 
 f EB 47 1923. 
 
 
 20m-l/22 
 
YB 155 
 
 VJ . 
 
 
m 
 
 r v 'A /?*. 
 
 ArvHAAAA-wvAA 
 
 
 
 A A! 
 
 iMlimri^^af^ 
 
 ^illsiS 
 
 .. r M 
 
 mm 
 
 A W-cs