1873J Engineering. 417 



by the chemist. It is therefore worth noting that quite recently Messrs. T. 

 Scheerer and^E. Drechsel have succeeded in obtaining crystallised fluoride of 

 calcium.* 



We are glad to observe that the excellent series of crystallographic " nets," 

 constructed and published some years ago by Mr. J. B. Jordan, has been 

 lately reproduced at a low price by Mr. Murby, of Bouverie Street. No better 

 means can be recommended to the student of crystallography, in mastering 

 the elements of this confessedly difficult subject, than the construction of a 

 set of pasteboard models from nets or outlines such as are furnished in these 

 sheets. 



ENGINEERING— CIVIL AND MECHANICAL. 



Water-Lifting Apparatus. — Prall's water-lifting apparatus, designed for 

 raising water into the tender tanks of locomotives, may be considered as an 

 offshoot from the Westinghouse air-break, and by its use the necessity of 

 providing pumping machinery at stations may in a great measure be obviated. 

 The nature of this apparatus may be thus briefly explained : — At or near the 

 bottom of a well is placed a closed box, with a valve on its under side, by 

 means of which it is kept full by the pressure of the water in the well. From 

 the top of this box are two pipes rising up above the ground ; at the 

 upper end of the one pipe, which extends to near the bottom of the box, is a 

 branch for conveying water to the tender ; whilst the other, which merely 

 enters the box at its upper side, is fitted at the other end with a branch, 

 which, by means of a length of flexible tubing and a union-joint, can be put 

 in communication with a pipe on the locomotive connected to the compressed 

 air-reservoir of the break. • This connection being made, the engine-driver can 

 merely, by turning a cock, allow the compressed air to flow from the reservoir 

 to the submerged tank, when it will, by pressing on the surface of the water 

 in the latter, force this water up the rising main, and enable it to be discharged 

 into the tender tank. On a sufficient supply of water having been raised, the 

 cock is shut, the joint with the air-cylinder disconnected, and the compressed 

 air from the submerged tank escaping allows the bottom valve to open, and 

 the tank becomes again charged ready for another operation. 



Retaining Walls. — In a paper read before the American Society of En- 

 gineers, by Mr. Casimir Constable, it was stated that a retaining wall is stable 

 when the amount of its weight about the point of rotation exceeds the 

 amount of a certain triangular prism of material back of the wall, about 

 the same point — the intersection of the line of rupture of the wall, and the 

 resultant thrust of the prism. Many formulae and tables for retaining walls 

 are presented for use, without a factor of safety, since walls proportioned 

 therewith — well built and carefully back-filled — have been permanent. Expe- 

 riments made on a small scale, in which the theoretic conditions were more 

 nearly fulfilled than in practice, show that such walls are stable, and point out 

 the reason why. The problem having been thus solved, a factor of safety may 

 be introduced in the formulae, which will allow for shocks, irregular workman- 

 ship, and uncertain material. The problem was then considered under these 

 several heads : — the angle of rupture, the height of the prism of rupture, and 

 the direction and point of application of the pressure of the prism. It was 

 shown that the prism of greatest pressure is given by the plane which bisects 

 the angle of repose, and that — 



P = iw x A 2 tan 2 i , 

 2 



in which P = the horizontal force which sustains the prism, w the weight per 

 cubic foot, h the height, and i the angle of the prism. 



Pneumatic Foundations. — A paper on this subject was read before the Ame- 

 rican Society of Civil Engineers, at New York, on the igth of February last, 

 by General W. Sovy Smith. From that paper it appears that the first two 

 bridges on pneumatic pile foundations, erected in the United States, were — 



* "Journal fur Praktische Chemie," 1873, No. 2, p. 63. 



