42r, 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Dkcember, 



Eaton lloilgkinson seem to show that tlie ultimate strength of cast iron is in 

 the ratio of some function of the specific gravity dependant upon the follow- 

 ing conditions : viz. 1. the bulk of the casting ; 2. the de))tli or head of metal 

 under which the casting was made ; 3. the temperature at which the iron was 

 poured into the mould ; 4. the rate at which the casting was cooled. 



Tahle XI. All the irons experimented on are arranged in classes, according 

 to the cliaracter of the fracture; for which piu'pose the terms — 1. silverj', 2. 

 jnicaccous, 3. mottled, 4. bright grey, 5. dull grey, and 6. dark grey, have 

 been adopted hy the author as a sufficient basis on which to rest a uniform 

 system of nomenclature for the physical characters of all cast irons, as recog- 

 nisable by their fracture ; and it is to be wished that experimenters in future 

 would adopt this or some other uniform syitem of description, in place of 

 the vague and often incorrect characteristics commonly attached to the ap- 

 pearance of the fracture of cast iron. 



The twelfth and last table contains the results of a set of experiments on 

 the important subject of the increase of density conferred on east iron, by 

 being cast uniler a considerable head of metal, the amoimt of which conden- 

 sation had not been previously reduced to numbers. It shows this increase 

 of density in large castings, for every 2 feet in depth, from 2 to 14 feet deep 

 of metal. 



A very rapid increase of density takes place at first, and below 4 feet in 

 depth a ncaily uniform increment of condensation. 



The importance of these results is obvious ; for, if the ultimate cohesion of 

 castings is as some function of their specific gravity, tlie results of experiments 

 in relation to strength, 7nade on casfiuffs of dijferent magnitudes, or cast un- 

 der different heads, can only be made comparable by involving their variable 

 specific gravities in the calculation. 



June 2 — The President in the Chair. 

 The following were balloted for and elected : — Lieutenant T. il. Sale, B.E., 

 and George Larmer, as Associates. 



June 16 — The President in the Chair. 

 The following were balloted for and elected : — William Joiy Henwood, as 

 a Member ; John Thomas Cooper and John Oliver York, as Associates. 



" On the Action of Steam as a Moving Power in the Cornish Single Punip- 

 ing Engine." By Josiah Parkes, M. Inst. C. E. 



In this communication, the author presents a detailed analysis of some of 

 the facts collected and recorded by him in his former communications, with 

 the special object of ascertaining from the known consumption of water as 

 steam, the whole quantity of action developed — the quantity of action had it 

 been used unexpansively — the value of expansion — the correspondence be- 

 tween the power, and the resistance overcome— and, finally, a theory of the 

 steam action, with a view of determining the real causes of the economy of 

 the Cornish single pumping engine. 



The data employed for the purposes of this investigation are those obtained 

 from the Iluel Towau engine by Mr. Henwood, from the llolmbush by Mr. 

 Wieksteed, and from the Fowey Consols, and recorded in the author's com- 

 munications in the Transactions of the Institution of CivU Engineers, Vols. 2 

 and 3. 



Steam may be applied in one or other of the two following modes : expan- 

 sively, that is, when admitted into the cylinder at a pressure greater than the 

 resistance, and quitting it at a pressure less than the resistance ; or unexpan- 

 sively, that is, when its pressure on the piston is equal to the resistance 

 throughout the stroke. By the term economy in the use of steam, is meant 

 the increase in quantity of action obtaiued by the adoption of that mode 

 which produces the greatest effect. 



The weight of pump-rods, &c., which effects the pumping or return stroke 

 in a Cornish engine is greater than the weight of the column of water, by the 

 amounts necessary to overcome the friction of the water in the pipes — to dis- 

 place the water at the velocity of the stroke — to overcome the friction of the 

 pitwork, and of the engine itself. The absolute resistance opposed to the 

 steam, consists of the weight which performs the return stroke, plus the fric- 

 tion of the engine and pitwork, and the elasticity of the uncondensed steam. 



The water-load in the Huel Towau engine was very accurately ascertained 

 as 11 lbs. per square inch on the piston ; and it is shown that the additional 

 resistance amounted to 7 lbs. in the Huel Towan, and to Gibs, in the other 

 engines, so that the whole resistance in the Huel Towan engine is 18 lbs. per 

 square inch of the piston. Ts'ow, the elastic force of the steam at the termi- 

 nation of the stroke, and before the equilibrium valve is opened (ascertained 

 from the ratio of the volumes of steam and water consumed), is only 7 lbs. 

 per square inch, that is, 4 lbs. less than the water-load alone. The corres- 

 ponding results for the other two engines are equally remarkable, and show- 

 most distinctly that, at the termination of tlie stroke, the pressure of the 

 steam is far below the water-load, as had been previously observed hy Mr. 

 Henwood and others. 



The next step in the analysis is to determine the portion of the stroke per- 

 formed when the pressure of the steam in the cylinder is just Ijelow the re- 

 sistance, and tlien to separate and estimate the spaces through which the 

 piston is driven respectively by steam of a pressure not less than the resistance, 

 and less tlian the resistance. These facts being ascestained, the virtual or 

 useful expansion, and the dynamic efficiency of the steam, during the two 

 portions of the stroke, are known ; and it appears that there is a deficiency 

 of power, as compared with the resistance overcome, of above 3 lbs. in the 

 Huel Towau, and more than 4 lbs. in the other engines, per square iuch on the 

 piston. 



From these startling facts, and a careful examination of Mr. llcnwoorl's in- 

 dicator diagi'ams, the author was induced to inquire whether the jiiston had 

 not lieen impelled by a force altogether distinct from the continuous action of 

 the steam upon it, namely, by a force which is to be referred to the sudden 

 impact on the piston when the admission valve is so fully and instantaneously 

 0|>ened, as it is in these engines, and a free communication established be- 

 tween the cylinder and the boiler. To this instantaneous action on the pis- 

 ton, the author, for the sake of distinction, assigns the term percussion ; and, 

 proceeding to analyse the authentic facts under this view, it appears that the 

 space of the cylinder though which the piston was carried by virtue of this 

 percussive action was about 21 inches in the Huel Towan, 27 inches in the 

 llolmbush, and 33 inches in the Fowey Consols engines. 



The resiUts thus unfolded, which are facts independent of any hypothesis, 

 appear less startling on a full consideration of the circumstances under which 

 the steam is admitted into the cyhnder. The engine has completed a stroke, 

 and is brought to rest by the cushion of steam between the piston and the 

 cyhnder cover ; a vacuum is formed on the other side of the piston ; the 

 elastic force of the steam in the cushion then nearly balances the resistance. 

 A communication is now suddenly opened between the cylinder and the boiler 

 containing steam of a high elasticity ; and the piston, being ready to move 

 with a slightly increased pressure, receives a violent impulse from the steam's 

 instantaneous action. The piston having started, the influx of the steam is 

 more or less retarded by the throttle valve, and its elastic force, though at 

 first greater than the resistance, is soon reduced considerably below it, the 

 mass of matter in motion acting the part of a fly wheel, absorbing the excess 

 of the initial power over the resistance, and discharging it by degrees until 

 the stroke is completed. 



The indicator diagrams, which are the transcripts of the ])iston's move- 

 ments, show that such may be the nature of the action on the piston, and 

 the discussion of numerous well-established facts and phenomena, for the 

 Cornish engines, strongly confirms this view of the case. Whatever may be 

 the theory of the steam's action, the fact that the sum of those actions has 

 carried the piston through its course, is certain ; and it seems equally certain 

 that the quantity of water as steam which entered the cylinders was insuffi- 

 cient alone to overcome the resistance. 



The author then investigates the amount of useful action due to the steam 

 imprisoned between the piston and the cylinder cover, and recovered each 

 stroke, which, for its use in bringing the engine to a state of rest at the end 

 of the return stroke, he terms the cushion. This quantity, though small, is 

 appreciable, and its value is assigned for each engine. 



The author treats lastly of the evidence furnished by the diagi'ams of the 

 indicator, and of its utility as a pressure gauge. The communication is ac- 

 companied by elaljorate tables of the results of the analysis, and an appendbc 

 with the calculations worked out in detail. 



SCIENTIFIC SOCIETY. 



The opening meeting of the present Session was held by the Scientific So- 

 ciety on Thursday evening, Nov. 19, at their rooms in Great Russell-street, 

 Bloomsbury. In the absence of the President, one of the Vice-Presidents, 

 John Stevens, Esq., delivered the annual address, in which, after adverting 

 to the advanced position of the institution, he explained, at some length, its 

 characteristic features, and the pecuhar objects which it is designed to pro- 

 mote. The great and known want of adequate facilities for collecting and 

 registering scientific observations, seriously impeded the progress of inductive 

 generalization, — facts are lost for want of channels through which they may 

 be brought to a common centre, and there has never yet been formed a 

 Museum of recorded and classified data, to which the scientific inquirer may 

 resort for evidence to snp^iort or subvert theoretical views. The leailing pur- 

 pose of the Scientific Society is to supply this deficiency, but they can only 

 hope to succeed in so arduous an undertaking, by the most active individual 

 exertion, and by the friendly co-operation of those who are interested in the 

 advancement of science. After the address a paper was read on a new dis- 

 covery in Electrotype. The meeting was numerously attended, both by mem- 

 bers and visitors, which evince the interest taken in the proceedings of the 

 societv. 



KING'S COLLEGE. 



We understand that regretting the necessity of refusing many applications 

 for admission of students, whose age and previous character were not suffi- 

 ciently advanced, into the civil engineering department — and feeling at the 

 same time the advantage of having their previous education directed to those 

 studies, which would ground them in the subjects of the more extensive read- 

 ings of the senior class, and convinced as well, that even to a general studeu 

 would be useful, some knowledge of the principle and nature of that me- 

 chanism and machinery which is now becoming the subject of every day re- 

 mark and conversation', witliout which the education of the gentleman is 

 scarcely complete, the council of the college have established a junior class 

 for students of 14 years and upwards. 



