685 



MINING. 



MINING. 



698 



In 1769 



1772 



From 1778 



to 1815 



1820 



1826 

 1827 

 1828 

 1829 

 1830 

 1859 



the old atmospheric engine, 

 by consuming a bushel of 

 coals, raised . . . 



as improved by Smeaton . 

 the steam-engine as im- 

 proved by Watt 

 as improved by the Cornish 

 engineers . . . . 



5,500,000 Iba., 1 foot high. 

 9,500,000 



20,000,000 



28,000,000 

 30,000,000 

 32,000,000 

 37,000,000 

 41,000,000 

 43,350,000 



about 54,000,000 



The above statement, it should be observed, refers only to the aver- 

 age duty, many of the best engines having always greatly exceeded 

 this ; and at the present time the duty of the best engines in Cornwall 

 varies from about sixty to eighty millions. In the latter case there- 

 fore one bushel of coal performs as much work as fifteen bushels 

 effected seventy years ago, or as was accomplished by four till within 

 the last five-and-forty years. When it is stated that some of the 

 most powerful engines in Cornwall consume from three to four 

 thousand bushels of coal per month, that some mines employ several 

 such engines, and that the mere expense of drainage is 12,000/. or 

 13,000i. per annum, the importance of the improvements above noticed 

 will at once be appreciated. 



Independently of the vast and practically unlimited power which 

 the steam-engine places at our command, it may be considered as uni- 

 versal in its application, and entirely unrestricted by those limitations 

 of local circumstances which circumscribe the utility of all other 

 modes of drainage. The steam-engine may be erected on any spot 

 which convenience requires, and it may be made of .whatever degree of 

 power may be considered requisite ; fuel and water alone are needed 

 for it* operations ; and while successive improvements have reduced 

 the former to a fraction of its earlier consumption, it can always supply 

 itself with the latter from the ground. This independence of local 

 circumstances is of the more importance to the miner, as it is not in his 

 power to make choice of localities : the manufacturer may erect his mill 

 wherever water-power is abundant for driving his machinery, but the 

 miner must carry on his operations on whatever spot nature has de- 

 posited her mineral treasures, and make the best of circumstances 

 over which he can have no control. Thus the steam-engine smokes 

 in the narrow valleys of Cornwall, almost at the sea-level, on the 

 verge of the cliff at Botallack, and on the elevated table-land of 

 Mexico. 



The steam-engines employed for drainage are erected close to the 

 shaft in which the pumps are fixed, which is called the " engine-shaft;" 

 one end of the beam hangs over the centre of it, and is attached to the 

 pump-rod, which is raised at .each stroke of the engine, afterwards 

 sinking with ita own weight, which is always counterbalanced by a 

 " balance-bob," as before explained, so that the whole power of the 

 engine is exerted in raising the column of water in the pumps. The 

 engine is generally enclosed in a large substantial building, either two 

 or three stories high, which affords convenient access to every part of 

 it. The centre of the beam is supported by the front wall of the 

 house, and a low building attached to it contains the boilers, which in 

 'Cornwall, together with the steam-pipe and cylinder, are carefully 

 caged and covered up with some non-conducting substances. The 

 arrangement of the engine, with that of the " capstan" and " shears" 

 used in raising and lowering the pit work, is shown in Firj. 7. The 



Fig. 7. 



engines employed in draining mines have generally cylinders of not less 

 than 40 inches in diameter, and the cylinders vary from that size to a 

 diameter of 80 or 90 inches, the latter being the largest size ever con- 

 rtructed, and estimated at 300 home-power. The chief peculiarities of 

 the Cornish engines consist in using high-pressure steam (40 or 50 Ibs. 

 to the square inch) expansively, by cutting off the communication with 



the boiler at one-fourth or one-fifth of the stroke ; in allowing a short 

 interval between each stroke for the perfect condensation of the steam, 

 and in carefully preventing the radiation of heat from the boiler, cylin- 

 der, &c. The engines employed in our collieries present no peculiarity 

 worthy of notice, nor has any great attention been paid to their 

 improvement, owing to the cheap rate at which they can be supplied 

 with fuel. 



Support. The support of mines is the next subject which requires 

 our attention, and the extent to which it is necessary will depend very 

 much on the nature of the inclosing rock, which may be either so hard 

 as to stand of itself, or so soft as to crush .together unless the exca- 

 vations be properly secured. The mode of support used in mines is of 

 three kinds : by leaving pillars of the vein, as before noticed, for which 

 purpose the poorer masses are of course selected ; by timbering ; and 

 by walling either with brick or stone. Timbering is a very common 

 and convenient plan, and is thus practised : In the case of a shaft, 

 four pieces of timber of the requisite strength are framed into each 

 other and fixed within it at intervals of about four feet apart, the 

 intermediate ground being supported by driving thin boards between 

 each set of timbers and the rock. Levels are supported by three pieces 

 of timber placed in the form of a doorway, rather narrower above than 

 below, and framed together at the top (see Fi'j: 8), the ground between 



each of these doorways being supported in the manner above noticed. 

 Shafts and levels are sometimes also supported by walling, and in 

 coal-mines the pits are generally lined throughout with brickwork. 

 The " gunnies," or large open excavations from which the ore has been 

 taken, are kept open by strong pieces of timber placed across them, and 

 pressing against the two walls of the vein, which they thus prevent 

 from closing together, as might otherwise be the case, especially where 

 the vein was much inclined, and the pressure of the unsupported 

 hanging wall is consequently great. These open spaces are very useful 

 for disposing of the deads and rubbish which are continually accumu- 

 lating underground when the workings are carried on in the rock or in 

 unproductive parts of the vein, and which it would be useless and 

 expensive to raise to the surface. For this purpose a " stull " is formed 

 by placing strong timbers in the backs of the levels, upon which boards 

 are laid, so as to form a close covering on which the deads and attle (or 

 rubbish) are then thrown, till the space above has been completely 

 filled up. The pressure of this mass gives it sufficient solidity to sup- 

 port the walls of the vein in an effectual manner ; but notwithstanding 

 the large quantity of rubbish thus disposed of in mines, a great deal 

 always remains to be taken to the surface, as the waste heaps on the 

 surface of every mine will show. 



Ventilation. The ventilation of mines is more generally and more 

 effectually accomplished by a judicious arrangement of the works and 

 frequent communication with the surface than by mechanical means, 

 although it sometimes becomes necessary to resort to the latter. It 

 will be evident that in mines constructed on the principles which have 

 previously been explained, the disposition of the shafts, levels, and 

 winzes is such that the entire workings will always be traversed by 

 currents of fresh air, and it is only in particular cases where circum- 

 stances prevent the sinking of a shaft in places where it may be 

 required, or where great delay is experienced in effecting the usual 

 communications, that any mechanical process of ventilation is rendered 

 necessary. A very efficient machine for this purpose was invented 

 some years ago by Mr. John Taylor. It consists of a cylindrical 

 exhausting apparatus, which may be fixed at the mouth of a shaft or 

 level, and placed in action by any convenient power, when, by means of 

 a series of tubes connected with it, the foul air is extracted from the 

 interior of the works, and of course the pure atmospheric air rushes in 

 to supply ita place, and complete ventilation is thus effected. In 

 sinking shafts, a very simple contrivance is often found sufficient : 



