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THE CIVIL 1]\C:INK1<:R AM) A lU'IllTKCTS JOURNAL 



[May, 



(ity of powdor ox|)emlotl on each block, then the following will be the 

 resu'ls oliliiineil (Voia tlu; four experiments. 



1G5 cubic feet was blasted asiuuler by 12 ounces of gunpowder, 

 wliioh is at the rate of l-il.i ounces of powder for each cubic yard. 



ISO cubic feet was blasted asunder by 12 ounces of gunpowder, 

 which is at the rate of 1-SO ounces of powder for each cubic yard. 



r>{0 cubic feet was blasted asunder by 38 ounces uf guiipowder, 

 which is at the rate of 1-'.K» ounces of pow'der for cacli cubic yard. 



81; I cubic feet was blasted asunder by 04 ounces of gunpowder, 

 wliiidi is at the rate of 2 ounces of powder for each cubic yard. 



Therefore in the large loose limestone blocks about 2 ounces of gun- 

 powder may \i2 taken as the expenditure being necessary to bhist out 

 each cubic yard. The four blocks on which these experiments were 

 inade, were not at all cubical, although the one which contained 5'1() 

 cubic feet was nearly so. From the above results i beg to submit 

 some calculations regarding the force of the explosion of gunpowder, 

 being as the cube of the length of the Hue of least resistance. 



We are in possession of the (juantity of gunpowder used in blasting 

 the four blocks, and also of the solid feet contained in each of thein. 

 Extracting therefore the cubic root of the cubical contents of each 

 block, we shall then have their masses all in cubical form as follows: 



Cubic feet in each block. Side of the cube. 



■■•-/IGS - . 5-484 



'^180 - . 5-G4G 



W5iQ . . 8-143 



■U^8«4 - . 9-524 



Taking Ihc lengtli of the line of least resistance at each of these 

 cubes to be equal to (he distance from the centre to the nearest point 

 on the sin-face, or erjuid to half the side ot" the cube, then the follow- 

 ing will be the lengths in feet of the lines of least resistance. 



lu cube No. 1 — 2-742 feet. 

 No. 2 — 2-823 

 No. 3 — 4-071 

 No. 4 — 4-762. 



The cpiantilies of gunpowder consumed to blast asunder a line of 

 least resistance, of 



165 cubic feet blasted asunder. 

 180 diUo. 

 540 ditto. 

 864 ditto. 



If 105 cubic feet be blasted asunder by 12 ounces of gunpowder, the 

 line of least resistance in that mass, if in cubical form, will be 

 V 1G5 = 2-7'12 feet. 



Then the line of least resistance for one foot in cubical form w ill be 

 pquaj^ to S cubic feet. Then if 165 cubic feet with a line of resistance 

 of 2-742 feet require 12 ounces of gunpowder to open it, then 8 cubic 

 leet with a line of resistance of one foot will require 0-5S2 ounces of 

 gunpowder to open it asunder. 



The following are the quantities of gunpowder required to open one 

 foot of least resistance through the white limestone, as determined by 

 the blasting of the four blocks. 



Cubic feet in each block ... I65 



Quantity of powder used to rend it as- 

 under, in oiincet! - - . . ]2 



Cubic feet opened by the line of resistance 



of one foot . . . . . 8 



Quantity of powder required to open the 

 line of least resistance of one foot, in 



ounces 0582 



Mean 0-508 oz. 



Apply the rule of the cube of the length of th(- line of least resist- 

 ance, and working with the element just obtained from the four ex- 

 ]>eriments, to open asunder the line of least resistance of one fool. 



No. 1 — Then (lie scale of the length of the line of least resistance in 

 No. 1, 2-742' feet uuiltiplied by 0-582 ounces, the ([uantity of powder 

 to open one foot will be 2-742' =^ 20-02 X -582 = 12 ounces. 



No. 2— For a line of least resistance of 2-823 feet will be 11-95 

 ounces, 2'8-23' = 22-42 x -533 = 11-95 oimees. 



No. 3— -For a line of least resistance of 4-071 feet, will be 37-97 

 ounces, 4-071-' = t;7-45 X -jiiS =37-97 om.ecE. 



No. 4— For a line of least resistance of 4-702 feet, will be 01 

 ounces, 4-702' = 107-983 x '593 = 04 ounces. 



It is therefore clear from these experiments made that (he force of 

 the explosion of gunpowder is as the cube of tlie length of the line of 

 least resistance. Taking the mean quantity of gunpowder obtained 

 irom the four experiments to open asimder a line of resistance of one 

 foot, -and wlUch is 0-508 ounces. The following will be the results 



2-742 feet was 12 ounces, 

 2-823 - 12 ditto, 

 4-071 - 38 ditto, 

 4-762 - 64 ditto, 



180 



12 



540 



38 



864 



64 



0-533 0-5C3 0-593 



caleulated according to the cube of the length of the line of least re- 

 sistance. 



2-7123= 20-62 X 0-568 = 11-71 oz. = lC5 cubic feet. 

 2-823-^= 22-42 x 0-568 = 12-73 07,.= 180 

 4-07P= 07-45 X 0-568 = 38-31 oz. = 540 

 4-7623=107-933 X 568 = 61-33 oz. = S64. 



In having described the mode of blasting the white limestone on the 

 Antrim coast road in (he north of Ireland. It may be usefid as well as 

 interesting to the engineer to describe its qualities, and to what extent 

 it may be employed in the construction of works. 



In treating of the nature of any kind of material to be employed in 

 building, the first consideration is its character, to resist decomposition 

 whether placed inthe 0])enair exposed to the full action of (he atmos- 

 phere, or buried in the earth, or entombed in the deep. Its indura- 

 tiim and compactness of structure, the absence of figures, the mass it 

 can be had in, and the facility of working or tooling it into form. 



The white limestone on tlie Antrim const road lies in beds dipping 

 slightly to the plane ; it is generally quite white, but sometimes it is 

 of a yellow'ish tint; it is traversed by very small veins of calcareous 

 spar, but the most remarkalile feature is the quantity of Hints it con- 

 tains, they are dry, grey and black ; the thickness of the beds of the 

 white limestone is very singular, being sometimes more than 30 feet. 



This white limestone is not good for building, because it moulders 

 by exposure to the atmosphere, it is not therefore generally used in 

 any public building, although it might be used in filling up the interior 

 parts of walls: it is inferior for road metal, being tender and wearing 

 quickly ; it can be procured in large masses, when reduced to pieces 

 containing six, twelve and eighteen cubical inches, it breaks into irre- 

 gular fragments with sharp edges. 



The white limestone when placed under the sea is particularly sub- 

 ject to the ravages of the pholas, and is therefore unsuitable to be 

 employed in the construction of marine works, such as harbours or 

 breakwaters, &c., it is however a valuable niaterial for making lime 

 for building, and for agricultural purposes. In our quarrying o])er.i- 

 tions we rarely found in it shell remains. 



In quarrying it out in large masses, the blocks sometimes had what 

 the workman call a lean and a full bed; the lean bed being less than 

 an angle of 90", and the full bed more than 90°. The white Limestone 

 can be split with plug and feather, or pooled by wedges; if the strati- 

 fication be in thin beds, it opens across with a very rugged and irregu- 

 lar face, but if very solid ami compact, and the beds of great thickness, 

 it will open more evenly and equal in the face. It dresses readily 

 with the hammer, and can be wrought and hewn into any form. I am 

 however of opinion that the white limestone of the county of AKtrim 

 shouhl not be used in constructing any work requiring durability, be- 

 cause it is a rock liable to decomposition when exposed to the atmos- 

 phere. 



I have already, in the paper on blasting the white limestone, alluded 

 to the small fissures which traverse that rock, and which also traverse 

 the blue and grey limestone of Ireland, and vvhicli the stone-cutters 

 call scull veins doublers, on account of their exact resemblance to the 

 sutures in the human scull. 



In concluding, I beg to mention that there are several species of the 

 Phohis. I.amarh in his natural history, mentions the Pholade Dactyle 

 or Pholas Dactylus, as btdng very prevalent on the coast of France, 

 and also inhabiting the shores of the Biitish seas. I have given a 

 sketch of the Phoyhis Dactylus, antl I beg to present to the Institution 

 a very beautiful specimen of this kind, from which the sketch has been 

 made, and which specimen I have accidentally obtained in London. 

 There is another species called the Pholade Scrabrelle, or Phohrs Can- 

 dida, which inhabits the European seas, and a veSy small kind called 

 by the French Saxicave Ridee, Saxicava Rugosa. It is quite foreign 

 to the object of this paper to enter into any thing like giving an ac- 

 count of all the various kinds of Pholas, or their habits; it is quite 

 sufficient to the engineer to know that every deserijttion of calcareous 

 rock, when placed under the sea, is subject to be perforated by those 

 bivalves ; indeed every rock upon which acids act are subject to be de- 

 stroyed by them, ansl it consequently has been conjectured that they 

 possess the power of producing an acid that decomposes the rock con- 

 taining calcareous matter; on the other hand some maintain this is 

 not the case, because the acid would also decompose the shell which 

 covers them. Mr. Lonsdale, of the Cieologieal .Society, mentioned to 

 me that some marine works constructed at Plymouth were much in- 

 jiu-ed by the ravages of the Pholas. Beds of calcareous rock of several 

 feet in thickness, in the Frith of Forth have been enturely destroyed 

 by the Pholas. 



It will be seen that the sliell of the Pholas Dactylus, presented to the 

 Institution, is very tender and delicate ; from the extreme fragile nature 

 of the shell it would not be supposed capable of destroying indurated 



