3 88 MINING 



perature from 90 to 98 degrees, and saturated air currents of a velocity of from 400 to 

 500 feet per minute, with more or less vitiated air, are conditions which are very trying, 

 and give a low labour efficiency. Vitiated air will impair labour efficiency to a greater 

 extent than a high temperature. 



Observations made with the object of determining the rate of increment of temper- 

 ature with depth have shown considerable divergence in different places. The following 

 results of temperature observations (quoted in the Report of the New Zealand Royal 

 Commission on Mines, 1912) show the depth in feet required in various localities for an 

 increase of i deg. F.: Comstock, U.S.A., 33; Witwatersrand, Transvaal, 208; British 

 collieries (mean), 64; Bendigo, Victoria, 77; Ballarat, Victoria, 80; Thames, New Zea- 

 land, 43.5; Waihi, New Zealand (approx.) 32.8. In a valuable paper by J. Whitehouse 

 and W. L. Wotherspoon (Jour. Chem. Met. 6 Min. Soc. of S.A., May 1911) the mean 

 temperature rise in the deep level mines on the Rand is given as i deg. F. for 253.9. ft- 



Efforts have been made to counteract high temperatures in mines, by compressed 

 air refrigerators, water-injectors and increased ventilation. Dr. Dietz (Oest. Z.f. Berg, 

 u. Hiittenwesen, 191 1, Vol. lix, p. 430) advocates the thorough cooling of a small portion 

 of the incoming air and then mixing it with the remainder. He uses for this purpose a 

 refrigerating-engine, air turbine, turbo-compressor, and a steam-turbine. 



Prof. Jacob Koenigsberger, of Freiberg, while conducting investigations regarding 

 the depth of the boreholes, found that the increase in temperature does not take place 

 uniformly, but that it proceeds much more rapidly in boreholes sunk in the neighbour- 

 hood of ore deposits, the reason being presumably that, owing to certain chemical proc- 

 esses, heat is constantly generated there. In the vicinity of coal measures the tempera- 

 ture increased by one degree for every 26 to 30 metres. The change was particularly 

 rapid near mineral oil deposits, where every 8 or 1 1 metres of increased depth advanced 

 the temperature by i degree. Prof. Koenigsberger draws from his observations the 

 conclusion that from the change in the temperature of boreholes the occurrence of coal 

 or mineral oil within 200 metres of the bore may be prognosticated. (See also Koenigs- 

 berger and Muhlberg, Trans. Inst. Min. Eng., Vol. 39, p. 617, 1910). 



A borehole at Czuchow in Austria, for the purpose of proving coal, in 1909 reached 

 the great depth of 7,350 ft. 



VENTILATION. Ventilation questions have during the past two or three years engaged 

 much attention, especially in view of the requirements of recent enactments in regard to 

 the quantity and character of the mine air. The Coal-Mines Act, 1911 (Section 29 (3) ) 

 for the first time in Great Britain provides for a definite standard of ventilation; i.e., a 

 place shall not contain less than 19 per cent of oxygen or more than i j per cent of CQs, 

 whilst the samples taken in an intake airway must not show an average percentage of 

 inflammable gas exceeding one quarter. There are exemptions from the former provi- 

 sion in the case of mines liable to spontaneous combustion. The Act also provides for 

 the classification of mines according to the amount of inflammable and noxious gases in 

 the main return airway, thus paving the way for a system of division, as followed in 

 France and Belgium, for imiting the use of certain types of illuminants and explosives. 

 In France and Belgium the system has been extended so as to provide a classification in 

 which due consideration is given to the dual factors of firedamp and coal dust. 



According to the new French regulations a percentage of more than 2 per cent of gas 

 is to be considered dangerous in a working place. The permissible limit in headings is 

 1.5 per cent measured in the return, and i per cent in the return from other working 

 places, but the regulations are more elastic than those now in force in Great Britain. 



With the tightening up of the restrictions and the new requirements as to the qualifi- 

 cation of officials, increased attention has been paid to the apparatus for measuring and 

 testing the atmosphere of the mine. Briefly, the apparatus used for the detection of 

 firedamp may be classified as follows: (i) Instruments depending on the comparative 

 rates of diffusion of methane and air. (2) Instruments dependent on specific gravity. 

 (3) The observation of the glowing appearance of a platinum wire rendered incandescent 

 by electricity. (4) Instruments depending on the fact that the electrical resistance of 



