832 HYDRAULIC CRANES 



be a certain amount of friability from this cause ; and therefore, when it is important 

 to have no swelling, as in blocks of concrete which have to be lifted, recourse must 

 be had to slaked lime, or else to cement, which contracts rather than expands in 

 setting. In the one case the concrete is long in hardening, having more moisture in 

 it than the lime can absorb; and in the use of cement more expense is incurred. 

 Portland cement is, however, not so expensive as might at first appear from the 

 cement being double the price of lime, because the proportion to the ballast may be 

 considerably reduced. 



HYDRAULIC CRANES. The application of water-pressure to cranes is due to 

 Sir Wm. Armstrong. These are now so generally applied, that although the subject 

 belongs properly to Engineering, it is thought advisable to include some notice of these 

 valuable and interesting machines in this work. A statement made, by the request 

 of the British Association in 1854, by the inventor himself, so completely explains all 

 the peculiarities of these cranes, that the paper is reproduced from the 'Proceedings ' of 

 the Association. 



4 The employment of water-pressure as a mechanical agent having recently under- 

 gone a great and rapid development, I may be permitted to make a few observations 

 on the successive steps by which its present importance has been attained. In so 

 doing I shall commence with the year 1846, in which, after many preliminary experi- 

 ments, I succeeded in establishing, upon the public quay at Newcastle-on-Tyne the 

 hydraulic crane which has formed the basis of what has since been effected. 



4 This crane both lifted the weight and swung round in either direction by the 

 pressure of water, and was characterised, like all other hydraulic cranes since made, 

 by remarkable precision and softness of movement, combined with great rapidity of 

 action. 



* The experiment thus made at Newcastle having proved satisfactory, I soon after- 

 wards obtained authority, through the intervention of Mr. Harley, the Dock Surveyor 

 of Liverpool, to construct several cranes and hoists upon the same principle at the 

 Albert Dock in that town, where they were accordingly erected, and have ever since 

 continued in operation. 



4 The next place at which these cranes were adopted was Grimsby New Dock, where 

 an important step in the advancement of this kind of machinery was made on the 

 suggestion of Mr. Rendel, who pointed out its applicability to the opening and closing 

 of dock gates and sluices, and instructed me to extend its application to those objects. 

 An extensive system of water-pressure machinery was accordingly carried out at that 

 dock, and the result afforded the first practical demonstration that the pressure of a 

 column of water could be advantageously applied as a substitute for manual labour, 

 not merely for the cranage of goods, but also to give safe and rapid effect to those 

 mechanical operations which are necessary for passing ships through the entrances of 

 docks. 



4 In all these instances the moving column of water was about 200 feet in elevation. 

 At Newcastle and Liverpool the supply was derived from the pipes communicating 

 with the town reservoirs, but at Grimsby a tower was built for supporting a tank into 

 which water was pumped by a steam-engine. In the former cases, the fluctuation of 

 pressure, consequent upon the variable draught from the pipes for the ordinary 

 purposes of consumption, proved a serious disadvantage ; but this objection had no 

 existence at Grimsby, where the tank upon the tower furnished a separate source of 

 power, undisturbed by any interfering conditions. Nothing could be more effectual 

 for its purpose than this tower; but, in the natural course of improvement, I was 

 Bubseqently led to the adoption of another form of artificial head, which possessed 

 the advantage of being applicable, at a comparatively small cost, in all situations, and 

 of lessening the size of the pipes and hydraulic machinery, by affording a pressure of 

 greatly-increased intensity. 



4 The apparatus thus substituted for a water tower I named " tlie Accumulator" from 

 the circumstance of its accumulating the power exerted by the engine in charging it. 

 The accumulator is, in fact, a reservoir giving pressure by load instead of \yclevation, 

 and its use, like that of every provision of this kind, is to equalise the strain upon the 

 engine in cases where the quantity of power to be supplied is subject to great and 

 sudden fluctuations. 



4 The construction of the accumulator is exhibited \nfig. 1170, and needs but little 

 explanation. A, cylinder; u, plunger; c c, loaded weight case ; D, D, guides for ditto ; 

 E, pipe from pumping engine ; F, pipe to hydraulic machine. It consists of a large 

 cast-iron cylinder, fitted with a plunger, from which a loaded weight case is suspended, 

 to give pressure to the water injected by the engine. The load upon the plunger is 

 usually such as to produce a pressure in the cylinder equal to a column of 1,500 feet 

 in elevation, and the apparatus is made sufficiently capacious to contain the largest 

 quantity of water which can be drawn from it at once by the simultaneous action of 



