1846.] 



THE CIVIL ENGINEER AND ARCHITECFS JOURNAL. 



253 



piece of touchstone ; before each of these rubbings there is 'aid on with a 

 brush a thin coat of plaster of Paris or marble cement, raised with water to 

 the consistence of milk; and lastly, should the colour of the stone or marble 

 be clear, a coat of wax, or mixture of wax and turpentine, is laid on and 

 rubbed with a linen, cotton, or woollen rag, till the marble or stone becomes 

 perfectly polished, but if the colour of the marble or stone should not be 

 clear before applying the wax, or mixture of wax and turpentine, it is rubbed 

 with linseed oil till the colour becomes clear, taking care to remove all the 

 oil before the wax is applied. In addition to the above process, sometimes 

 the marble or stone to be polished is rubbed with a piece of jasper, if a very 

 brilliant polish is required. Other materials used in the construction of 

 houses are to be polished in same manner as the marble and stone above de- 

 scribed, till the rubbing is completed with the Charley Forest stone ; they 

 are then rubbed with linseed oil, taking care to wipe it off thoroughly, and 

 then varnished with gum lac in the following manner: — Take a ball of wool, 

 wet the surface of it with the varnish, and cover it with a linen rag. Then 

 well rub the material to be polished, adding a little oil occasionally, if the 

 varnish should not work freely. To dye and colour marble or stone, and 

 other materials used in the construction and decoration of houses, the same 

 system of acids, salts, or colouring matter is employed as generally used by 

 dyers in dying cloths and other textile fabrics. The said acids, sails, or 

 colouring materials, or their chemical combinations, are applied in a liquid 

 state, over the surface of the material required to be dyed or coloured by 

 means of a sponge. If the dyed or coloured surfaces are to have the same 

 polish as the rest of the surface, the said colouring materials are applied 

 before polishing the said substance, or when the process of polishing is only 

 half finished ; but if it be wished the dyed or coloured matter to be dead or 

 unpolished, the colouring materials are applied after the process of polishing 

 is completed. The certain other materials alluded to in his title are plaster, 

 stucco, scagliola, and a species of stucco invented in France, and introduced 

 by the inventor for the first time in England, and which is called stiic a la 

 brosse. The claims are : — First, the filling up with plaster of Paris, or mar- 

 ble cement, in the manner above described, the pores of the marble or stone 

 intended to be polished, and rubbing them with certain hard stones, as here- 

 inbefore described ; secondly, the polishing of certain other materials used 

 in constructing or decorating houses, &c. ; and thirdly, in dyeing and colour- 

 ing marble, stone, and other materials, as above described, by wetting them 

 'With certain acids, salts, colouring materials, or their chemical combinations, 

 as above described, by means of a brush or sponge. 



GRAND BLAST AT THE DOWNHILL TUNNELS, LONDON- 

 DERRY AND COLER.\INE RAILWAY. 



The novel nature of the undertakins proposed by the Londonderry and 

 Coleraine Railway Company, has, from its first appearance before the pub- 

 lic, invested that project with peculiar interest to scientific and the mone- 

 tary world. 



Lough Foyle, a deep indentation of the sea on the northern coast of 

 Ireland, covers an area of about 00,000 acres. With the exception of the 

 channel along the Donegal shore, leading up to the port and city of Lon- 

 donderry, the tide in this lough does not generally rise more than six feet, 

 and, at low water, a large portion of its area is left perfectly dry, exposing 

 a slob formed of the richest alluvial deposit, capable of immediate conver- 

 sion into valuable soil. The situation of the lough — almost land-locked, 

 protected from the swell of the Atlantic by its narrow entrance, and shel- 

 tered from the prevailing westerly winds by the mountainous nature of the 

 country on the Donegal coast — is such as at once to suggest the idea of 

 facility for shutting off the sea, and reclaiming a great portion of the slob 

 land. lo the Session of 1837, an Act of Parliament, authorising this re- 

 clamation, was obtained, and two enclosures were made, winning from the 

 sea about 4000 acres, upon part of which luxuriant crops have already 

 been reared. In 1844, public attention became alive to the necessity for 

 establishing railway communication between the important towns of Lon- 

 donderry and Coleraine. The mountainous nature of the interjacent coun- 

 try, rendered a line inland impracticable, and the idea was conceived of 

 combining the Railway and the Foyle reclamation, making one embank- 

 ment serve for both. With this object a Company was formed; terms 

 were arranged with the parties in whom rested the powers under the Act 

 of 1837 ; and, in the Session of 1845, the Londonderry and Coleraine Rail- 

 nay Company obtained its Act of incorporation. 



The length of line proposed by this Company is 39 miles, including a 

 branch to the town of Newtown-Limavady — 15 miles to be constructed on 

 an embankment through Lough Foyle; and by which embankment about 

 22,000 acres of land will be recovered from the sea. Of this reclaimed 

 land, 12,000 acres are set apart to cover the expenditure on the railway. 

 The works are now so far advanced, that by the end of the present year 

 the Directors anticipate being in a position to enclose and sell a portion of 

 the land ; and, as the works proceed, like portions may from time to time 

 be enclosed and sold. 



The line, after leaving Lough Foyle, proceeds eastward across Magilli- 

 gan Point, and along the coast towards Coleraine. About seven miles 

 from the latter town, and close tu Downhill, the beautiful residence of Sir 



Hervey Bruce, Bart., if passes through the cliffs between Downhill Hoose 

 and the sea by two tunnels, one about 700 yards and the other about 300 

 yards in length. The works upon those tunnels have been some lime ia 

 progress by the ordinary process of picking and blasting; but it being 

 deemed necessary to expedite their construction, it was determined toefliect 

 the removal of the obstructing rock by one grand blast. 



ROCK BEFORE THE EXPLOSION. 



ROCK AFTER THE EXPLOSION. 



We are indebted to the Illustrated News for the following particulars 

 relative to an extensive blast which took place at Downhill, about 7 miles 

 from Coleraine, on the (ilh June last : — " The mass of rock which it had 

 been originally necessary to remove was at the western mouth of Ihc- large 

 tunnel, and measured nearly 60,000 Ions, the material being the hard ba- 

 saltic stone, iu which the coast of Antrim and Londonderry abounds ; a 

 large portion of this rock bad been previously removed by the common slovr 

 process already named. Having resolved upon the large blast, Messrs. 

 Bromhead and Hemming, the contractors, formed a heading or gallery into 

 the rock, from the side of the clilT, 50 feet in length : at the end of this, a 

 shaft was sunk, 22 feet to the level of the railway, as seen at C A ; and 

 again another gallery at the bottom, running at right angles to the first gal- 

 lery, and furth-T into the rock, was made for 10 feet. At the end of this 

 was placed the large charge of powder, 2,400 lb., shown at A. The whole 

 was then well filled op, aud tamped with clay and masonry, and the wires 

 to convey the electric fluid from the battery through the charge were care- 

 fully arranged. The smaller charge, which was higher up in the ruck, 

 and which is seen at B, contained 000 lb. of powder; aud the gallery B F 

 leading to it was about'70 feet in length ; this was also tamped in a similar 

 manner to the larger one. The galvanic battery, which stood on a siied on 

 the top of the clilf, was a very powerful one, consisting of 18 cells, each 

 cell about 14 inches square. 



The operations were conducted by Mr. Hemming and Mr. Webb, Super- 

 intending Engineer lo the Contractor. Mr. M'Leod, acting under Mr. 

 Robert Stephenson, the Engineer of the Company, was present, with Mr. 

 Langon, and other civil engineers. There were also several royal esgi- 

 neers and scientific gentlemen who had come from different quarters of the 

 country to witness the explosion. 



At the appointed hour some little delay occurred in connecting the wires 

 with the battery ; but, at half-past three o'clock, the two poles were united, 

 and instantaneously the bottom of the rock was seen lo heave out for a 

 moment, the mass of rock above stood, trembled, and, cracking; into a thou- 

 sand fissures, rolled into the sea beneath. A deep and hollow souo<l was 

 heard, like distant thunder, but no report. The quantity of rock removed 

 must be upwards of 30,000 tons. The effect will be seen by referring to 

 the accompanying profiles or sections taken through the lines a a h b, in 

 the front view, both before and after the blast. The result, in an engineer- 

 ing point of view, was perfectly successful, and reflects the greatest credit 

 on the gentlemen superintending the operation. 



The dotted lines show the quantity of rock lo be removed. A is the 

 larger chamber, containing 340Q lb. of gunpowder, c, the beading leading 

 to it, which is 50 feet in length. B, the smaller chamber, containing (iOO 

 lb. of powder. A x, the line of least resistance — 50 feet. From A to the 

 top of the cliff— 1 05 feet. 



