1840.1 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



301 



stirrup irons, &c. These articles, after having been cast, undergo a 

 process of (leoxi(l;ition, which gives them a surprising degree of tena- 

 city, with great flexibility and a capacity of polish resembling steel ; 

 those castings, not intended to receive a polish, present surfaces capa- 

 ble of receiving and retaining tin for a considerable length of time. 



To return to the date where we left off, we may observe that the 

 improvements which had been made had increased the power uf the 

 furnaces, from which as well probably as from their concentration a 

 diminution had taken place in their number. In a prospectus drawn 

 up about the year 1720, near the time of the .South Sea Bubble, we find 

 the number of furnaces rated at only .59, but as this list is manifestly 

 imperfect, we are perhaps bound to considerthe number aslaiger. Sus- 

 sex, Kent, and Hampshire were then the seat of l.i furnaces, now of not 

 one. Resuming the histi.ry of pitcoal iron we find that after the time of 

 Dudley, nothing of importance was done imtil 1740, when a new 

 auxiliary, the steam engine, had come into the field. The application 

 of this machine gave the manufacturer greater liberty in selecting the 

 site of his works, and enabled him to erect larger furnaces with a pro- 

 portionate quantity of blast. From this d^ite the use of pitcoal every 

 year became more prevalent, and has ended by superseding charcoal 

 in this country. In aid of this two other circumstances operated with 

 advantage, the inlroduction of Mr. Watt's double blast engine, and the 

 invention of puddling and rolling bar iron by Mr. Cort. 



In our own days improvements not less important have been effected, 

 and since the commencement of tlie literary career of the author, whose 

 work is now before us, the quantity of pig iron necessary to pioduce a 

 tun of bar iron has been reduced from 40 cwt. to 2o or 27 cvvf., with 

 almost as great an economy of fuel. '1 his has principally been accom- 

 plished by means of the hot blast, the use of which however can be 

 onlv C(;nsidered as recently established, so strong was the prejudice 

 against its application. One gre.it property it possesses is that it 

 diminishes the qu mtity of vitreous matter formerly required in the 

 furnaces, so as to diminish the consumption of both fuel and limestone. 

 An equalization of the blast is another result, so as to dimmish the 

 effect of the atmospheric influence, which it is well known interferes 

 vritli the oper.itions of the furnace. In this, as in other countries, a 

 larger produce of cast iron is obtained in the winter months than dur- 

 ing the summer or autumn, while the quality of the metal is improved 

 by being nuRh more carbonated and less fuel is consumed. During 

 the months of June, July and August, more especially in hot seasons, 

 the qiialily of the iron in this country will be depreciated 3U per cent., 

 and the quantity very considerably reduced, and in many parts of 

 .Sweden, says Ivir. Mushet, when the summer heats are intense, the 

 manufacturer is obliged to blow out or stop his furnace for two or 

 three months ; not only is he unable to make carbonated metal, but is 

 frequently incapable of keeping the furnace in such trim as to make a 

 produce of any quality whatever. 



An improvement scarcely inferior in importance, although only local 

 was the discovery by the author in 1801, of the Mushetstone or Black 

 Band ironstone, a new class of carboniferous ironstone, principally 

 found n^ar the river Calder, near Glasgow, but also in South Stafford- 

 shire, NcM'th Wales, and North Statibrdshire, in which latter district 

 it is called Red Mine. Although used by Mr. Mushet in the Calder 

 iron works, so strong was the prejudice ag.iinst it that it was not until 

 1825 t.liat its application was at all extensive. It is now used in about 

 50 furnaces in Scotland, and the quantity of iron produced is above 

 100,0;JO tons ; on one estate alone £12,0J0 is received as royalty in 

 consequence of this discovery. A powerful auxiliary in the hands of 

 the Scotch masters has been the use of raw pit coal, and coking under 

 dust, which have been found to be particularly suited to the Scotch 

 coal and iron. A dawning discovery and one which promises to be 

 not less important than that of the Mushetstone, is Mr. Crane's process 

 for smelt ng iron with anthracite, thus making available a large supply 

 of mineral wealth, and extending our national resources. 



»4 Practical Inquiry into the Larvs of Excavation and Embankment 

 upon Hallways, being an attempt to develop the natural causes which 

 affect the progress of such works, Sfc. By a a Resident Assistant 

 Engineer. London : Saunders and Otley, 1S40. 



It may be laid down as a general axiom that in every inquiry of this 

 nature, the degree of dependance which shall be placed upon the 

 laws established, should be proportionate to the extent and generality 

 of the experiments on which such laws are founded. 



If we take as our groundwork the gross performances of a long 

 series of months during which the attendant circumstances as to weather, 

 state of the earth, as it may be wet or dry, adhesive, loose, or crumb- 

 ling, and so troublesome or otherwise in filling and teaming, with all 



the other circumstances by which earth-works are affected, we shall 

 be afjle to deduce from these in connection with detailed experiments 

 ujion the requisite particulars of getting, filling, teaming, and times of 

 travelling, a tolerably perfect set of expressions by which calculations 

 mav be made with reference to earth works in general. 



it must be borne in mind, however, that ail results derived from 

 such expressions, however acc\irately determined, and however com- 

 prehensive the data from which they have been derived, are still liable 

 to be affected by circumstances which no liuman foresight can predict. 

 All that can ever be with safety relied upon is, that supposing all at- 

 tendant circumstances to be identical as to effects with those which 

 had place during the period of former observations, then that the cal- 

 culations applied to other works varying in form and magnitude, shall 

 give results agreeing with such former observations. 



But if we attempt without reference to the gross performance during 

 some long period, to derive from the observation of a few days, fixed 

 laws for the actual time of executing large works, it is obvious how 

 impossible it must be to derive correct results in any such way. The 

 days during which the observations have been made, may have been 

 remarkably fine or remarkably unfavourable, or in some intermediate 

 stage between these. But whatever this stage may have been, there 

 is no alternative but to adopt them as our standard for the whole year, 

 and thus it will be seen on what an unstable foundation such a struc- 

 ture must be raised. 



We do not mean to sav that any experimentalist would so far stultify 

 himself as to proceed blindly on the isolated experiments of certain 

 days on which tlie performances would notoriously be either much less 

 or much more than on the average of the year, but we can readily 

 imagine that the imputation of improper selection can scarcely fail to 

 apply more or less to the experiments of any 10 or 12 single days at 

 any period of the year. Let us suppose on the one hand one of the 

 dull gloomy days of our winter months, the ground slowly parting with 

 the frost which had hardened it for some weeks before — the falls of 

 earth possessing more than usual tenacity, the workmens' tools clogged 

 with the soft retentive clay adhering to every thing like bird lime; 

 the rails clammy and dirty from the same cause, the wagons when 

 teamed retaining a third of their contents plastered to the sides and 

 bottom, and so requiring double the time for teaming, and then let us 

 with this contrast a fine dry day of spring or autumn, the rails almost 

 free from dirt, the shovels all clean and bright, and parting instantly 

 with t!ie contents filled into the wagons. 'These latter again wlfen 

 tipped immediately discharging their contents, and leaving none to be 

 shovelled out by the teamers. And let us ask any man, practical or 

 not practical, on which day the performance will be greatest. We 

 shall not hesitate to say that the performance on the one day shall be 

 50 per cent, more than on the other, and shall be independent of the 

 number of hands employed, because assuming that on the favourable 

 day each department of the labour is occupied by the proper pro- 

 portion of men and horses, then on the unfavourable day an increased 

 number will rather serve to impede than to hasten, as they will be in 

 each others way, and the hands will at intervals have to wait for their 

 turn to exert themselves, it being im,iossible that more than a certain 

 number at a time can be fully employed. 



We repeat we have no intention of charging the experiments before 

 us, or anv otiier of the same kind with such glaring absurdity as would 

 attach to them, did they exhibit the extraordinary results of one or 

 other of the extremes we have pointed out as a foundation for esti- 

 mating the work of the year, but we contend the chances are, that as 

 isolated experiments they bear more or less to one or other of the ex- 

 tremes. It is barely possible that the days selected shall represent a 

 fair average of what may be done throughout the year. 



It is for such reasons that we would hesitate before adopting as the 

 basis of important calculations, the results of a few days observation. 



We would much rather rely on well authenticated records of the 

 performance during many months, under different systems of working, 

 and we would suggest to the author of the present treatise, and to all 

 others who may in future undertake experimental inquiries of this na- 

 ture, that the really practical and experienced, whether engineers or 

 contractors, will invariably, as their test upon the accuracy of any par- 

 ticular theory, however derived, proceed at once to compare the re- 

 sults which such a theory will give them with their own actual know- 

 ledge of what has been done on the great scale in other works. They 

 will therefore pronounce the theory correct or otherwise, according as 

 it coincides or disagrees with their own experience. We are thus 

 over and over again impressed with the importance of founding all 

 theories upon the actual performance of as long a period as possible. 



Let it not be understood that we are here objecting to experiments 



in detail. These are exceedingly useful, because placing as they do 



before our eyes the precise amount of time occupied in all the various 



tages through which the soil passes from its original position in the 



