October 1, 1895.] 



KNOWLEDGE 



227 



the heat of the lamp. The other lamp is shown in section. 

 The flame of the lamp is surrounded by glass ; but if the 

 course of the arrows is followed, it will be seen that the 

 air, both on entering and leaving the combustion chamber, 

 passes through gauze, indicated by broken lines. 



At present it is sufficient to state that with the increas- 

 ing fcpeed of air currents of the improved ventilation, the 

 simple Davy lamp soon proved iinsafe, and has been 

 unanimously condemned by the various commissions 

 appointed to inquire into the matter in England, France, 

 Germany and Austria. 



The Davy lamp and many of its successors gave a very 

 feeble light, and hence the various efforts made to improve 

 the Ught-giving power of safety lamps. But much increase 

 of lighting power never appears to be attained without the 

 introduction of some disadvantageous element, and it is 

 a question whether a safety lamp has yet been discovered 

 which is really efficient in all points, although there are 

 many that are safe under most conditions obtaining in 

 coal mines. Many people think that it is for electricians 

 to solve the problem. This may possibly be correct, but 

 as yet electric lamps are defective in one or two points — 

 a very important one being that to which attention is now 

 CO be drawn — the detection of fire-damp, choke-damp, and 

 white-damp, in the atmosphere of coal mines, a point 

 which, considering the intimate connection existing between 

 the first of these gases and fire-damp explosions, and 

 between the other gases and loss of life or injury to health, 

 is naturally of paramount significance. 



Ever since the importance of adequate ventilation has 

 been recognized, the advisabUity of being able to test the 

 atmosphere of a coal mine for dangerous gases has also 

 been admitted. It is well kuown that a safety lamp flame 

 only burns normally so long as the atmosphere is 

 moderately pure. When it becomes mixed with other 

 gases, to even a small extent, the flame of the lamp 

 becomes altered in appearance. It elongates, and is 

 surmounted by a feeble luminous flame known as a " cap," 

 which increases in size with the proportions of fire damp. 

 Between two and a half and three per cent, of fire-damp 

 in the atmosphere has in this way a visible effect on the 

 flame of an ordinary safety lamp burning oil. As, however, 

 any interruption in the ventilating current, or a small 

 additional emission of gas, or the presence of dust, is 

 capable of rendering such an atmosphere very dangerous, 

 it has been everywhere accepted tUat it is no:essary to 

 keep the fire-damp in the atmosphere of dusty and fiery 

 coal mines below one per cent. 



Fire-damp detectors of greater delicacy than the ordinary 

 safety lamp have become necessary, and have from time 

 to time been introduced. In them various properties of 

 fire-damp have alternately been called into requisition, in 

 order not only to indicate the presence of this objectionable 

 gas, but also to show the extent to which it is present, 

 even when only amounting to less than one quarter per 

 cent. Some of these indicators are designed to examine 

 in the laboratory samples of air previously collected in the 

 mines, whilst others indicate on the spot in the mine 

 itself the proportion of fire-damp present in the atmosphere. 

 The latter are evidently the more appropriate for daily 

 use, and to these alone attention will be drawn here. 

 Ine Pieler lamp is a large Davy safety lamp, burning 

 alcohol. This lamp has served well the purpose of a 

 delicate portable indicator of tire-damp ; but being by no 

 means free from danger, it has undergone considerable 

 improvement at the hands of Chesneau, and has been 

 made very much more efficient, so that the flame now 

 exhibits a change of colour, as well as the production 

 of a " cap," in the presence of gas. Yet it does not give 



unqualified satisfaction, as it is a non-illuminating lamp, 

 and necessitates the carrying about of an extra lamp for 

 lighting purposes. As a matter of course this point has 

 received attention, and attempts have been made to over- 

 come this detrimental feature. 



It has been known for some time that a hydrogen flame 

 is a still more delicate indicator than an alcohol flame. 

 It, therefore, occurred to Prof. Frank Clowes that by 

 having within an ordmary safety lamp a little burner 

 that could be fed as required with hydrogen, the latter 

 would ignite at the oil flame, which could then be 

 extinguished by drawing down the wick in the ordinary 

 way, by means of the pricker ; the amount of fire-damp, 

 even though it was only a quarter per cent., could then be 

 readily gauged by measuring the height of the cap. The 

 oil flame could then be re-established by pushing the wick 

 up, the hydrogen flame turned off, and the lamp used in 

 the ordinary manner for lighting. Prof. Clowes has 

 successfully accomplished all this in the lamp illustrated, 

 and provides a portable supply of 

 hydrogen sufficient to make a large 

 number of estimations of fire- 

 damp, the hydrogen being con- 

 tained under pressure in the small 

 steel cylinder which, when 

 attached to the lamp, not only 

 furnishes a reservoir for the neces- 

 sary supply of fuel for the delicate 

 testing flame, but also acts as a 

 convenient handle by which the 

 lamp may be held up for exami- 

 nation. More recently two 

 engineers, M. Legrand in France 

 and Mr. Stokes in England, have 

 constructed lamps on the Clowes 

 principle, in which, however, the 

 testing flame is supplied with 

 alcohol instead of hydrogen. 



It now seems imminent that the 

 present position of this section of 



the fire-damp question, like the ventilation section, is a 

 question as to which refinement shall be used in order to make 

 us utilize in the best manner the knowledge and appliances 

 we now possess, and we may look forward to the battle of 

 indicators to keep us posted with the most recent experiment 

 and results in this important section of the question. 



As regards fire-damp explosions, therefore, we are at 

 present not only conversant with the conditions under 

 which they are likely to occur, but we have means provided 

 to prevent their occurrence — still they occur ! There are, 

 of course, unforeseen risks against which we cannot 

 provide, and which may account for some accidents ; but 

 still, one cannot help thinking that simple precautionary 

 measures should be more generally adopted, and, if 

 necessary, enforced by legislation. 



Hvdrogen Oil Testing 

 Laiu)). 



S>c<tn« Notes. 



Madagascar (that island which is attracting a good deal 

 of attention at present) lies almost entirely within the 

 southern tropic, and is one of the largest islands of the 

 world, its length being about one thousand miles, and its 

 average width two hundred and fifty miles. The tops of 

 its highest mountains are not much more than eight 

 thousand five hundred feet above the level of the sea. 

 The vegetation of Madagascar may be said to be arranged 

 in three zones — first, the tropical plains, varying in width, 

 and extending inland from the sea-coast ; second, forest 



