58 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Feb. 3, 



partly placed on buildings, in which I was concerned, and. to satisfy preju- 

 diced oljjeciions, it was expedient to have them removed, although the same 

 slates have been used elsewhere. At KiUaloe, where a few years back there 

 was a rude surfaced mountain in which only goats or very poor cattle 

 browned, there are now, owing to the slate rnck which prevails there, many 

 hundred men daily employed. At Valentia not less tl.an 200 are m daily 

 work, and probably half that number at Mr. Synge's in Wicklow The im- 

 portance of the encouragement of such a trade is therefore manifest ; for a 

 regular trade of this kind, with all its minor ramifications, is much more 

 beneficial to a country than the mere temporary employment on public 

 works, which, creating a temporary excitement, occasionally works more 

 mischief in the end than otherwise. At present the proprietor of the Va- 

 lentia quarries, who works them chicfiy for sawn flags, finds his principal 

 market in London, while articles of this kind required for Ireland are ob- 

 tained out of the country. , , • i, 



A similar remark may be made with regard to bricks. Good clay is abun- 

 dant in the country, an<l good bricks are made in some parts, and might be 

 made in many others ; but from the frefjuent indifierence as to the purchase 

 of good maleri.als, there is, in many cases, great carelessness in their manu- 

 facture. If, however, samples uf bricks, and particulars of the clay, were 

 collected, and the result of experiments made known, the good articles would 

 be encouraged, and the making of many of the perishable ones of the present 

 day, which are dear at the cost of carriage, would greatly decrease, and the 

 buildings of the country would thereby be improved. Again, there is a 

 strong prejudice against native bricks, which are really good. In illustra- 

 tion of this, I may mention a case connected with the manufacture of fire 

 bricks at Dungannon. which are of excellent quality, and remarkably well 

 made from the clay of the coal district, like those of Statlbrdshire ; but the 

 public, not knowing if they were really good, prefer buying the English fire- 

 brick. Their sale is, however, now, or was, some little time since, consider- 

 able ; but it arose from an ingenious, and scarcely to be condemned trick of 

 the maker, who stamped the word .Stourbridge on his bricks, and they then 

 had a ready sale as good Staffordshire brick. 



Before entering into the details of the experiments on the stones now be- 

 fore you, I would beg to advert to the important light in which ths study of 

 practical, or economic geology, is now viewed in the sister country, in con- 

 ilrmalion of the remarks which I have made. Previously to the building of 

 the new houses of parliament, a commission consisting of geolo.s;ists (accom- 

 panied bv the architect of the building) was appointed to investigate the va- 

 rious qualities of the diflerent convertible building stones of the country. 

 The result of their experiments has now been published in the parliamentary 

 papers, (and this Jouriml. Vol. IV.) and has been received with the greatest 

 satisfaction. It has also had the important effect of originating a museum of 

 economic geology, for displaying the properties of the dilTerent stones of the 

 country, in order that practical information on the various materials, with 

 the chaiacters which experiment and observation of the present state ol those 

 materials used in ancient structures supply, may prevent the continuance ot 

 the very numerous failures which have attended the use of many stones em- 

 jdoycd in different parts of the country, and which, being of inferior quality, 

 have brought to speedy ruin many noble and interesting buildings. The in- 

 stitution referred to is now supported at the expense of government, and is 

 under tlie direction of the distinguished geologist Sir H. De la Beche: con- 

 nected therewith is a curaior, and a laboratory for an analytical chemist, by 

 whom experiments are made on various rocks, and wlio aHords. at a fixed 

 charge, any information required relative to the various propenies of rocks 

 for building, mining, or agricultural operations. I recently had an opportu- 

 nity of visiting this museum, but found less really useful information for the 

 architect and practical builder tlian I expected. It, however, contains mos) 

 valuable and in;eresting collections of models, illustrative of the strata of 

 the earth, the working of mines, and the minerals themselves in their several 

 progressive stages from the mine to the manufactured article. From the 

 constitution of ihe institution, at present, h>avever, in its inlancy, it does not 

 appear to me to represent the spirit of a department in which the minds of 

 those most inleresteil in building operations are engaged ; and from the con- 

 trary opinion wilh reference to the Dublin Geological Society, combining as 

 t does scientific and practical geologists under its most intelligent and zealous 

 curator, I augur that with perseverance most useful and interesting results 

 will fiow from tlieir labours. 



Reverting to the more practical consideration of the subject, we find that 

 llie altered circumstances in the advanced civilisation of the present age, now 

 occasion the much greater use of the more convertible building stones, and 

 so variable are the different kinds of rocks in the degrees of hardness and 

 facility uf conversion, in their colour and their relative durability, that a 

 knowledge of these properties is now almost indispensable to the economical 

 erection of the structures ol the present day, as well as for the designing 

 any building, in which the bold simplicity and spirit of the ancient struc- 

 tures is to be embodied ; and hence the value of experiments and recorded 

 observation on the defective materials which ancient and more modern 

 buildings present, and without which expensive practical experience, and fre- 



quent failures will alone teach. The importance of attention to the good 

 quality of the building stones will be evident by reference to buildings in 

 Dublin, and to the already decaying nature of much of the granite in the 

 Four Courts, and portions of many other structures; and I may mention 

 that it is but a few years since, the necessity arose for restoring with new 

 masonry the walls of the extensive building of Trinity College Library and 

 the walls of the cathedral structures of Christ Church, and St. Patrick, m 

 the old buttresses of which latter buildings the effects of perishable stone 

 may now be seen. 



EXrERlME.NTS. 



The experiments which I have now to bring before the Society have been 

 made on nearly 600 specimens of the principal .stones of Ireland, which I have 

 from time to time in various ways collected together, and obtained chieHy 

 through the kindness of diiVerent parties, by whom they have been presented 

 to me, and among others I may mention the managers or proprietors of the 

 several slate quarries. I shall divide these experiments into three classes, viz. ; 

 — 1st. Absortion when immersed ; 2d, Resistance to fracture, or bearing 

 strength ; 3d, Weight necessary to crush these stones.— 1st, The results ot 

 the weight of water imbibed on immersion are \ery interesting, and disclose 

 some important facts. The size of the stones immersed was 14in. long by 3 in. 

 square, one half of which specimens are now in the possession of the society. 

 There were placed on their ends in 16 in. of water, and were uniformly im- 

 mersed for 88 hours, having been brought to a dry slate before immersion, by 

 being kept some time in a room at the ordinary temperature of domestic apart- 

 ments. They were carefully weighed before and after the immersion. (It would 

 be impossible to give in detail the results of these very numerous and extremely 

 valuable experiments, and it will only be in our power to notice the averages 

 given by Mr, Wilkinson). Of the six principal varieties of rock, viz :— Lime- 

 stone, sandstone, granite, basalt, and slates, the following are the results t— - 

 Ordinary limestone of Ireland— average weight per cubic foot in a dry state 

 (.53 different experiments) 1701b., least weight 1591b.; greatest 1801b.; ave- 

 rage absorption J.lb. ; least absorption nothing ; gieatest ditto i lb. The chalk 

 limestone of Antrim weighs 1601b. to the cubic foot, and absorbs 3 lb, of water. 

 The impure shaly calp limestone weighs 160 lb., and absorbs from 1 lb. to 41b. 

 of water per cubic foot. Sandstone average weight 'per cubic foot (from 38 

 specimens) 1451h.; least weight 1231b.; greatest ditto 1701b. The absorption 

 varies from nothing to upwards of 101b.. being exceedingly variable; the 

 average being 5J lb. Granite average weight per cubic foot 1701b.; extreme 

 weight 176 lb.; least weight 1431b. The Newry and Kingstown granite ab- 

 sorb |lb.; Carlowfrom U to 21b.; Glenties (Donegal, between granite and 

 gneiss) 41b. Basalt average weight per cubic;foot 178; extreme weight 1811b.; 

 least ditto 171 lb. ; absorption is less than Jib. to the cubic foot. Clay roofing 

 slate average weight of cubic foot 177 lb. ; extreme weight 1791b. ; least ditto 

 1741b.; absorption from nothing to less than Jib. Soft clay slate from near 

 Bantry absorbed about 2 lb. In these experiments the weight of the stone and 

 the alffiorption have been deter.nained by direct weighing, and not by taking 

 the specific graviiy. The latter mode would prob.ably give the most exact 

 result ; but from ihe small size of the specimens which would be operated on. 

 and from the variation in density, which is evident in ditierent parts of the 

 stones here experimented on, and which is common to must rocks, I ihink that 

 the result would frequently not approximate closer than that derived from di- 

 rect weighing in larger masses. For particular scientific investigation the 

 specific gravity is doubtless desirable, but for practical purposes the weight 

 of the stone and its absorption ascertained in its ordinary state, is, I conceive, 

 all that is useful or necessary for practical consideration. The limestones, it 

 will be seen, are among the least absorbent of the rocks, and being the must 

 abundantly used as a building material, it is obvious, that if good mortar be 

 use! in a proper manner in the external pointing, any weather may be resisted 

 in almost any situation, « ithout the use uf perishable rough cast or costly ce- 

 ment. B dldings. however, carried up in wet seasons, in which the external 

 mortar is not allowed to become hard, or where it becomes injured by frost, 

 cannot resist the weather, but with good mortar pointing inserted between the 

 stones from which the old joints have been raked out, I feel satisfied Irom ex- 

 jierience and from the result of cases to which I could refer, that no material 

 is more secure than these non-absorbent limestones. There is a popular error 

 with regard to limestone, which is very generally considered to he a stone that 

 will not keep out the weather ; its very non-absorbent quality is, however, the 

 cause of this idea, the stone condensing in the interior of the rooms the mois- 

 ture of the air. Sandstone and limestone, when properly used together, owing 

 to their different properties, make the best work; the absorbent quality ot 

 the sandstones keeping the interior face of the walls dry. and the exterior ot 

 limestone resisting the weather. I believe it is doubted if mortar will itself 

 resist [he weather ; that it will, however, when it is carefully and properly ap- 

 l>Iied, I feel a strong conviction, resulting from experiment, practice, and ob- 

 servation. And 1 may here remark what is calculated to strengthen the 

 opinion, viz. : the state of some of the external mortar in the old castles and 

 other ruins, where the plastered surface, after weeks of wet weather and heavy 

 rain, if struck with a hammer, will commonly show a dry dust very close to 



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