3G0 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[October, 



Prof. Sedgwick, after reviewing tlie general principle of Artesian wells, 

 described two districts in wljicli these operations were attended with verj- 

 different results. In the eastern part of Essex the chalk is covered by sandy 

 beds of the plastic clay, and these by several hundred feet of impervious strata 

 of London clay, all dipping together towards the east. The arenaceous beds 

 below the London clay rise higlier towards the chalk than the clay does, and 

 absorbs a considerable part of tlie water from the high grounds. Uy boring 

 through the clays to this sand, si)rings of water immediately rise above the 

 surface, and are carried off by natural channels. By this supply of water, the 

 Talue of the land has been materially increased, since the country, though 

 abounding in peat bogs, and stagnant ponds during winter, suffers much from 

 the summer drought. Tlie other attempts to form Artesian wells, referred 

 to by Mr. Sedgwick, were made near Lincoln, which, though surrounded by 

 •/ens, covered with water in the winter, is not sufficiently supplied during the 

 summer, liut the clays supporting the fens of the Bedford Level are below 

 the chalk, and though there are pervious beds beneath them, which rise to 

 the north-west, yet the clays are of such enormous ibickness that they have 

 never been penetrated ; and even were that accomplished, the high land is so 

 distant th.at intervening fissures, filled up with impervious materials, might 

 intercept the supply. Expensive sinkings have been made at Ljnin, and also 

 at Boston, aud after boring through many hundred feet of clay they have 

 utterly failed, and in any future operations in this district the chance of suc- 

 cess vvo\ild be very remote. Mr. Sedgwick then observed with respect to the 

 red colour of rocks mentioned by Dr. Moore, that he considered it simply 

 owing to the red oxide of iron which niigiit be present or not in any bed ; 

 sometimes the tinge was only superficial. In Nassau the red colour was owing 

 to vicinity of trap rocks. He also observed, as to the condition of limestone 

 rocks, that although they sometimes appear in masses, presenting a brecciated 

 appearance, shells and broken corals being cemented together, yet generally 

 they occur as regular parts of the series repeated without any regularity, in 

 formations of all ages. In position and inclination they resembled their asso- 

 ciated rocks, and partook in all their contortions aud dislocations, except so 

 far as their sohd masses would resist mechanical movements, better than 

 yielding deposits of sediment and mud. The organic remains found in lime- 

 stones only differed from those in the other beds of the same age as far as the 

 conditions differed under which each was deposited. At the present day 

 different families of corals grow upon a solid and a soft bottom. — The Rev. 

 \V. D. Conybeare pointed out the similarity between Artesian wells and mines 

 simk in the coal measures. Artesian borings had been made with success 

 near the outcrop of certain strata, but at a distance from this, although the 

 combination of strata was the same, they had failed, from the great depth 

 necessary to be penetrated. Now it is certain that the coal exists in many 

 places beneath the new red sandstone and magnesian limestone, but at such 

 depths that it would be hopeless to attempt to reach it. He therefore re- 

 commended to the attention of miners the formation of a series of Artesian 

 borings in some of the coal districts, beginning where the probability was 

 greatest, and proceeding from that point till the depth became too great. 

 Such a series of experiments would show the nature and depth of the strata 

 below, and over what extent coal might be worked without sinking shafts at 

 enormous expense and with the risk of complete failure. — Mr. Bartlett ob- 

 served, in confirmation of one of Dr. Moore's remarks, that where limestones 

 abounded in corals, as at Berryhcad, their structure was homogeneous, and 

 exhibited little trace of stratification ; when the corals were rare, the bedding 

 became distinct. 



" Some Inquiries into the Causes oy the increased Desttntctibility of ilodem 

 Copper Sheathing." By Mr. Prideaux. 



In May 1840 Mr. Prideaux was applied to by Mr. Owen, of Her Majesty's 

 dock-yard, to analyse some sheet copper from the sheathing of the SattspareH, 

 which had been on thirty years, aud was still in good condition. The sample 

 gave about 0'25 per cent, of alloy, chiefly zinc and tin. This contrasted well 

 with a sample rendered unserviceable in a very short time (in only one year), 

 and in w hich no quantity of alloy sufficient to weigh had been found ; and 

 the two agreed with two recorded analyses of Sir H. Davy and Mr. R. Phillips, 

 the former having detected, in a very good sample of sheathing, about -^^ 

 of tin; the latter having found the sheathing o! the 7'aWar frigate (almost 

 destroyed in four years, though never out of Sheerness harbour,) the purest 

 copper he had ever analysed ; and further with the reputed inferiority of the 

 recently prepared sheathing of the Royal Navy, which must have been much 

 purified by the repeated fusions it has undergone. The inference adduced 

 was, that the presence of tin and zinc was favourable to the durability of the 

 copper. Mr. Prideaux, however, proceeded with the analyses in other cases. 

 Pour were selected, viz. 



From the Copper on Annual loss. 



Minden 1 7 years 43 per cent. 



Ploeer only 5 11 



Linnet, copper rapidly destroyed, could not be taken off sound enough to 

 weigh a sheet. 



New-sheathiny prepared at Iler Majesty's mills, Portsmouth. 



There was no conformity between the results in these and the former ex- 

 periments ; they did not show any coincidence between the composition of 

 the sheathing and its durabihty. The next step, therefore, was to examine 

 how far it might be referred to any of the physical properties of the metal. 

 To ascertain this, slips from each sample, all of equal surfaces (4 + 0'5 inch), 

 were immersed each in a pint of sea water ; the five vessels being placed side 



by side, so as to set them all in like conditions. Sea-water being electro- 

 neutral, and acting slowly on copper, a Uttle sal-ammoniac was added, to 

 quicken the action without affecting the neutrality. The greatest waste was 

 on the SamparieV copper, which had worn tlie best of all ; the least on that 

 of the Plover, one of the worst. Thus, in the laboratory, under parallel cir- 

 cumstances, they do not observe the same order of durability and waste as 

 they had done in use. Tlie cause of comparative waste appears, therefore, 

 to be in part at least, due to external conditions, aud of these two classes 

 may be noticed : one depending on the connexion w ith the ship, the other 

 on the circumstances of her employment. Of the first class two suggested 

 tlieraselves — the position on the ship's side, and the nails by which the cop- 

 per is fastened. The lower part of a ship's copper seems to suffer much less 

 than the upper, so long as she continues in deep water ; but w hen she grounds 

 at low water, if on black mud, ibis part suffers most from the action of sul- 

 phuretted hydrogen, peeling off in blue flakes. The influence of the nails 

 offers rather more chemical interest. They are never of pure copper, and 

 being very numerous, all in contact with the copper sheets, whilst their heads 

 present also a considerable metallic surface to the salt water, tliey may pro- 

 duce very decided effects, cither preservative or destructive, by a slight elec- 

 tro-chemical difference. Mr. Prideaux therefore examined a vessel which 

 they were just then stripping, her copper being worn out in four years. It 

 was found that round some of the nails the copper was quite entire, for aa 

 inch or two, though worn ragged in other parts ; whilst elsewhere, and some- 

 times on the same sheet, the copper round other nails was quite gone, though 

 other fragments of the sheet remained. Here some of the nails appeared to 

 have exerteil a protective, others a destructive influence. To ascertain the 

 effect of the nails, five slips of new copper from the same sheet, and of the 

 same size, were suspended equidistant; and at the same depth, in a vessel of 

 sea water from the West Indies. The result was, that all the nails, except 

 one (which was from Her Majesty's dockyard), appeared to act destructively. 

 Here appears to be one instance of a protective nail, not enough so to prevent 

 all waste of the copper, which experience has shown not to be desirable ; but 

 doubtless the preservative power may be increased to any requisite degree by 

 attending to the composition of the alloy. The copper is alloyed chiefly with 

 tin ; but if the nail is at once hard and flexible the manufacturer is satisfied 

 without examining what other metals are present. If they were always made 

 just so much electro-positive to the copper as to protect the sheathing, so far 

 as compatible with their own durability, they would seem to offer the simplest, 

 most perfect, aud most convenient means of electro-chemical protection. The 

 damage to which the copper is subjected is affected by the circumstances of 

 the ship's employment. Sheathing suffers most where most subject to wash 

 and air, for friction is an agent in the waste as well as oxidation. It is also 

 well ascertained that the copper sheathing suffers most in hot climates, which 

 might be expected, upon a common chemical principle, that chemical action 

 increases with the temperature ; and it became a question whether this effect 

 of heat, as well as its tendency to promote organic production and decom- 

 position, might not form an important element in this destructive agency. 

 Mr. Prideaux therefore obtained w ater from different parts of the Gulf Stream, 

 with and without the weed, from the Caribbean Sea, and from Falmouth har- 

 bour, where the packets moored, the waters of which might possibly be 

 affected by the mine drainings discharged into the river. Whilst these were 

 being collected. Prof. Daniell's announcement of large quantities of sulphu- 

 retted hydrogen in the waters of the Guinea coast came before the public. 

 To try the action of these different waters five copper shps, of the same 

 dimensions, cut from the same sheet, were suspended in a pint each of the 

 following samples of water : 



1. Heart of the Gulf Stream. 



2. Ditto with the weed. 



3. Caribbean Sea. 



4. Falmouth harbour. 



5. Plymouth harbour. 



After thirteen days they were taken out and reweighed, having been put in 

 all bright, but cleaned, on taking out, only with a brush in soft water, as in 

 the other experiments : — 



1. 2. 3. 4. 5. 



Put in 16th 180-26 182-56 190 16901 176-41 



Out 29th - 17S-45 182-3 1896 168-55 1761 



Loss in 13 days 1-81 0-26 04 046 031 



No. 1, came out clean and bright, the others with tarnished surfaces, except 

 No. 2, which was blotched and speckled. The Falmouth water presented no 

 indications of being more corrosive than that of Plymouth, and Mr. Prideaux 

 attributed the great difference of waste in these two cases to same unobserved 

 difference of conditions in the experiment. But the excessive action of the 

 Gulf Stream water, he considered too decided to be doubtful. Not only the 

 quantity wasted, but the metallic clearness of the surface, showed a marked 

 distinction. " But to whatever extent the recently increased waste of sheath- 

 ing may fairly be charged upon the greater velocity, more constant employ- 

 ment, and greater consequent liabihties of weather and climate of our ships, 

 particularly of the commercial classes, as well as to difference in the nails, I 

 am incUned," said Mr. Prideaux, "to fear the fault is still to be sought in the 

 copper itself. I have it on the authority of Mr. Moore, that the Quarantine 

 cutter, generally at anchor in our harbour, was coppered in October 1832, 

 and her copper is now in a very good state. Her last sheathing held good 

 14 years. The Eddystone tender, which also moors in Catwater, was cop- 



