282 



THE CIVIL ENGINEER AND ARCHITECT S JOURNAL. 



[August, 



the cicclro-lyzatlon of tUe aqueous soliitioa of soda and potash, on the hypo- 

 tlicsis of these bodies heing composed of two equivalents, or atoms, of metal, 

 and one of oxygen. To determine this question he employs a solution of 

 dichloride of copper in muriatic acid, as being a substance composed of two 

 atoii:s of metal, and one of an electro-negative element. Its electrolysis gave 

 as the equivalent of copper, 52'S, 53'4, and 61 'G, numbers approximating 

 closely to C3'2, or double the atomic weight of copper. After a long train 

 of investigation, he concludes that there is no reason dcducible from the 

 theory of isomorphism for doubting the correctness of the rcoeived atomic 

 weights of silver, sodium, &c., but that the difficulty, or anomaly, if it may 

 be so called, should be considered as attaching itscli to the di-compounds of 

 topper ; and that Faraday's propositions on this subject remain uuimpeached. 



" On the SoluhiWy of Silica hi/ Steam; with an account of an erperiment 

 on the subject, conditcted in the Eaat Indies." By Julius Jeffreys, late of the 

 Hon. East India Company's Medical Establishment. 



The inner surfaces of a flue built of siliceous brides appeared to be ileeply 

 eroded by the ]iass,'>.ge over it of steam at a very high temperature, and frag- 

 ments of siliceous materials laid in the course of the current were partially 

 consumed. .\ siliceous crust was deposited on several vessels of stone ware, 

 coated with a micaceous glaze, placed in the upper part of the furnace, and 

 this crust was re-dissolved when the vessels were removed to a hotter situa- 

 tion in the same furnace. The auth.or notices the experiments of Dr. Turner 

 and others, which failed in showing the soluliility of silica by steam, in con- 

 sequence, as he conceives, of th.e heat having not been sufficiently great to 

 effect the solution. 



INSTITUTION OF CIVIL ENGINEERS. 



Fei. 4. — The President in the Chair. 

 Cn Steam Engines. 



The abstract of Mr. Parkes's communication {Journal, No. 31, p. 136.) 

 having been read, Mr. Enys remarked, that Mr. Parkes had adopted a diffe- 

 rent unit of power to the one he was accustomed to employ ; but that was a 

 point on which he was not disposed to insist, and he was prepared rather to 

 yield to Mr. Parkes's opinion where they differed. Agreement on terms was 

 very important, and he wished to see more accuracy introduced in the use of 

 certain terms relating to engines ; lie would confine tlie term " duty " to the 

 net work, and the gross work he would call " effect." In speaking of a loco- 

 motive engine, he conceived the goods carried to constitute the duty — the 

 whole mass moved, the effect. The duty in Cornwall is a theoretical term, 

 being the water which ought to be raised according to the column displaced, 

 but the whole of which did not reach the surface ; and the whole mass of 

 pump work, water, iVc.. set in motion is the effect. The duty is not com- 

 mensurate with the effect, as it is independent of friction and other expen- 

 diture of power. The pit-work is not always we'd executed, and is not imder 

 the care of the engineer. Duty in Cornwall is, in fact, entirely a commercial 

 question, it having been instituted as a check between the adventurers and 

 the engineer who originally undertook to perform the work of pumping for 

 a certain share of the saving of fuel to be made. There were three distinct 

 causes of improvement in Cornwall, viz., in the boilers, in the application of 

 highly expansive steam, and in the pit work. 



Mr. Wicksteed, in reply to a question as to the work now being performed 

 by the engine at Old Ford, stated the general result to be, that with small 

 Newcastle coals of inferior quality, and of such a size as to pass through a 

 screen of thrce-qnarter inch mesh, the duty amounted to 71 millions raised 

 one foot high with 94 tb. of coal. He had experienced great difficulty in 

 procuring good 'Welsh coal, but with some MerthjT coal he had recently 

 tried, the duty immediately increased to 91 millions. 



In tiie Old Ford engine, the steam is cut oft' at one-third of the stroke, and 

 the w atcr is raised by the weight of a mass of iron acting on the water at tlie 

 return stroke. With the ordinai-y valves there is a loss of about one-tenth, 

 but with the valves invented by Messrs. Harvey and West, used in the Old 

 Ford engine, there is no loss, and no perceptilile blow from the water on the 

 valves closing, although no air is admitted beneath. 



The speed of this engine varies from one stroke to ten per minute, accord- 

 ing to the demand for water. In Cornwall, it is thought that at slow speed 

 there is a considerable saving of fuel, but he is of opinion thiit there is no 

 difference in duty at a fast or slow speed, provided there is sufficient time for 

 opening and shutting the valves. 



As to the term duty, although it is important to know what is the ab- 

 solute quantity of water raised, yet that is not the whole effect. The engine 

 raises a certain weight of rods, which is its load, and this weight should, in 

 the return stroke, produce a certain given eft'ect in water brought to the sur- 

 face; but, owing to bad valves, leaks in the pumps, and other causes, the 

 iiantity of water raised is not equal to the calculated amount. We cannot 

 ay that an engine has not done its duty because a portion of the water is 

 lost. Two engines, equally good and of identical power, may not produce 

 equal results ; because one may be raising water close beneath the beam, 

 another, up a shaft at some considerable distance, by means of a series of 

 long horizontal-motioned pump rods ; the latter, again, may be doing a duty 

 of 20 millioas in working the pump rods only. 

 It was his intention shortly to present to the Institution a complete report 



of tlie work done by Ids engine, with drawings of every iiart ; but he was 

 waiting to have the opportunity of ascertaining the evaporation from the 

 Cornish boilers, as well as from those of a pumping engine of Boulton and 

 Watt's, also in use at Old Ford, so as to determine, at the same time, the 

 respective duty and consumption of steam by the two engines. 



Mr. Field insisted on tlie importance of distingiusliiug between the duty 

 and effect, by usiirg the former term for the water actually raised, and the 

 latter for the real power expended, lie understood these terms to be so 

 applied to engines for water works in London, and that effect included the 

 friction of the water iu the pipes, and all other causes of diminution of duty. 

 The real eft'ect should be ascertained from the pressure of the water at the 

 pump, as determiued by a mercurial gauge. It is generally unrlerstood tliat, 

 iu speaking of the real comparative cfl'ects of the water works engines in 

 London, it would be unfair to take the water raised, as the same power would 

 iu one case be expended in raising water lOtI feet, as is expended in another 

 case in raising water 200 feet. The pressure of the water at the pumps is 

 the proper standard of comparison. 



Mr. Parkes stated, that in his paper he had used the term duty as distin- 

 guished from the absolute power o( the engine. The same Cornish pumping 

 engine at different periods performs very dift'ercnt amounts of duty, although 

 the absolute power exerted by the steam is the same. This arises from ad- 

 ditions to the friction by new pump rods, and from other causes. The Cor- 

 nish result is below the real duty done by the engine, taking the term in 

 their acceptation of it, and using their mode of calCTdation for that which is 

 by them considered a purely commercial question. The only correct manner 

 of ascertaining the absolute power exerted by pumping engines, so as to 

 eonijiare them with rotative engines, is to take the pressure on tlie piston, 

 and the value of the vacuum on the other side at the same time. The term 

 duty expresses the true, useful, or commercial performance of the engine, but 

 is no measure of the absolute jiower of the steam, which has to overcome the 

 friction of the engine, pumps, rods, &c., in addition. 



Mr. Enys, iu reply to a question from Mr. Gordon as to the speed at 

 which an engine is worked with the greatest economy, stated the general 

 opinion in Corw.ill to be in favour of about 9 strokes per minute ; if there 

 was a pause of half a second Ijctwecn each stroke, the Cornish cngineei-s 

 were perfectly satisfied. The indoor stroke is usually at the rate of from 

 2D0 to 200 feet per minute, and the outdoor stroke about 140 feet. When 

 the number of strokes exceeds 9, the balance requires to be altered ; the 

 engine then runs out quicker, but requires a greater expenditure of steam to 

 bring it in again. In answer to a question relative to Woolfe's engines, he 

 believed they had never had a fair trial, as all tlie boilers originally adapted 

 to them were mu^h too small, and the tubes soon got full of oxide and mud ; 

 if the present system of Cornish boilers had been in use at the time, he 

 thought they would have acted mnch better. Some engineers are so much 

 impressed in their favour, that they are desirous of giving them a trial again 

 with all the recent improvements. 



ilr. Cottani mentioned an engine on M"oolfe's principle which had worked 

 peifcccly well for several years. It is now grinding a bushel of corn with a 

 fraction less than 4 It. of coal. The pressure of the steam iu the boiler is 

 from 22 to 25 lb. 



Mr. Cottam, in reference to the above discussion, at a subsequent evening 

 (Feb. IS) alluded to the pumping engine at Hammersmith, which forces the 

 water through five miles of pipes, and then through a vast number of smaller 

 pipes, and was subject to gre.at variations of service, and inquired how the 

 duty could be ascertained with any tolerable accuracy, as the v.iriable expen- 

 diture of steam under dift'ercnt circumstances must lead to considerable errors. 

 If a boiler, as in the Cornish engines, is adapted to raise the bob 7 times per 

 minute, and, owing to some cause, as the water not being able to get away, 

 the bol) is raised only 5 times per minute, there is two-sevenths iu favour of 

 the Ijoilcr; or if an engine adapted for 30 strokes per minute makes only 25 

 occasionally, there is great difficulty in comparing it with other engines. 



Mr. Doiikiu urged the necessity of keejiing the quality of the engine and 

 its commercial eft'ect perfectly distinct ; if a given weight be raised to a given 

 height, it must produce a given eftect minus the friction ; in water-works 

 engines the resistance opposed by the friction is very considerable, and being 

 very variable, it must not be allowed to interfere with the consideration of 

 the intrinsic quality of the engine; of two engines having equal power, one 

 may discharge, owing to these circumstances, more water than the other, but 

 if both be of the same construction and raise a given weight, whether the 

 water be discharged perpendicularly or forced through any length of hori- 

 zontal pipes, there can be no mistake as to the amount of the effect produced, 

 or, in other words, of duty performed, as that woidd be determiued liy the 

 weight naiscd if in a Cornish engine, or by the resistance overcome if in an 

 ordinary pumping engine. 



Mr. Wicksteed observed, that there was no difficulty in instituting a com- 

 parisou between the duty of a Cornish engine and of an ordinary water-works 

 engine, because by the former the water was raised through a perpendicular 

 shaft, and by the' latter forced through several miles of pipes, of varying 

 length and resistance. He had for several years ascertained, by means of 3 

 mercurial syphon gauge, the pressure at the pump piston, and this gave, with 

 perfect accuracy, the resistance overcome by the engine, whether arising 

 from the pressure of water raised to a given or varying height, or from the 

 friction in a great length of pipes. This was easily proved at Old Ford, 

 where the water was raised into a perpendicular column or stand pipe, in 

 which the level of the water would he that necessary for overconting the 



