718 



SCIENCE. 



rVoi,. U., No. 43. 



ENGINEERING. 



Effect of frost upon fire-plug casings. — Mr. 

 Allen J. Fuller referred to a general impression that 

 the freezing of the earth around fire-hydrants has a 

 tendency to gi'iije fast to the frost-jacket, and lift It 

 with the expanding or heaving earth, which he de- 

 nied for the following reasons. 1°. The frozen earth 

 slides on the surface of the frost-jacket, because its 

 expansion is greater than that of iron. 2°. As the 

 expansion of the earth must he in proportion to the 

 intensity of the cold, so will it be greater above than 

 below a given point: therefore the first foot of frozen 

 ground will have a greater upward movement than 

 that which is below it, and the second foot greater 

 than the third, etc. Thus it will be seen that the 

 earth below a given point rises more slowly than 

 that above, and its friction is opposed to the one 

 above. 3°. If this is true of feet, it is true of inches 

 and of portions of an inch : therefore there is a re- 

 tardation movement throughout. 4°. The upward 

 movement of the ground : the freezing being greatest 

 towards the surface, and such movement involving a 

 more complete fracture of the earth surrounding the 

 frost-jacket, it follows that the friction is less at this 

 point than that below it, and in consequence there is 

 less power to move upward than downward. Of 

 course, the above does not apply to any construction 

 that the frost can get beneath. 



Mr. Frederic Graff noted and described the form of 

 wooden casing which had been successfully used in 

 the early practice of the Philadelphia water-depart- 

 ment. 



In response to the theory advanced in regard to the 

 action of frost in raising the casings of fire-plugs, and 

 to the statement that if the base of a structure ex- 

 tended below the frost-line it would not be lifted, 

 Prof. Haupt remarked, that he thought the theory 

 was in part sustained by the fact observed by some 

 of the district surveyors, and verified by the accurate 

 measurements they were obliged to make, that fences 

 moved bodily to the south and east in consequence 

 of the action of the sun and frost upon the ground on 

 opposite sides of them. He thought, also, that the 

 deductions concerning the immobility of structures 

 resting below the frost-line were not fully sustained 

 by the facts; as in the north-west, where ice forms 

 rapidly, lie had heard of numerous instances of piles 

 driven for bridges, and extending some distance below 

 the frost-line, having been raised as much as five to 

 six inches in a single night; and he conceived the ac- 

 tion in this case to be similar in kind to that of piles 

 driven entirely through solid ground, the only dif- 

 ference being in the amount of the resistance offered 

 by friction and weight of pile. The water, in freezing 

 around the pile, acts upon it as a griper or vice ; and 

 the expansion of the various strata or laminae of 

 water, as tliey become converted into ice, acts as a 

 lever to force up the pile. 



Mr. Howard Murphy did not consider the case cited 

 by Prof. Haupt as parallel, as the so-called piles, being 

 driven through water and soft mud, were probably 

 columns resting upon their bases, and depending 

 but little upon the frictional resistance of the mate- 



rial through which they passed. Therefore the ex- 

 pansive force upward of the freezing water would be 

 opposed by little more than the weight of the pile; 

 whereas in a fire-hydrant casing, or otlier deeply 

 planted post, the presumably well-rammed material 

 around the whole length under ground would offer 

 such proportional frictional resistance as to cause 

 the freezing earth to slide up the post rather than to 

 lift it. If the ice could be supposed to act downwards 

 upon the piles in question, it is hardly likely that it 

 would have forced them farther home. — {Eng. club 

 Philad.; meeting Nov. 3.) [411 



An enormous steam ferryboat. — The Solano, 

 on the Central Pacific railroad ferry, between San 

 Francisco and Oakland, Cal., was built by the Harlan 

 & HoUiugsworth company of Wilmington, Del. 

 The boat is 494 feet long on deck, 406 on the water- 

 line, 110 feet beam, 6i feet draught, loaded. The 

 tonnage is given as 3,540. The engines are two in 

 number, beam-engines working independently, hav- 

 ing cylinders 62J inches in diameter, and of 11 feet 

 stroke of piston. These engines are each rated at 

 2,000-horse power. The boilers are S in number, of 

 steel, have 19,630 square feet of heating-surface, or 

 about 1,500-horse power according to a usual rating 

 (12 square feet to the horse-power). The wheels are 

 30 feet in diameter, and are fitted with 24 buckets. 

 There are four lines of rails on the deck; and 48 

 freight or 24 passenger cars can be carried at once. 

 — {Mechanics, Ju\y 2S.) E. H. T. [412 



Surface-condensers for marine engines. — 

 Cadet engineer J. M. Whitham, U.S.N., compares the 

 performance of surface-condensers of marine engines 

 with the results of a formula for required area of 

 surface constructed by him, and deduces a constant 

 for usual application. He obtains the expression, — 



in which 



S = square feet of condensing-surface, 

 W = pounds of steam condensed per hour, 

 L ~ latent heat of steam of temperature, T, 

 Ti = temperature of exhaust-steam, 

 T2 = temperature of feed, 

 t = mean temperature of circulating water, 

 c = coefiicient variable with efiiciency of surface, 

 k = conductivity of the metal (556.S for brass, 642.5 

 for copper). 



He finds the usual value of c to be 0.14S. He finds 

 that this figure may be increased ten per cent where 

 independent circulating pumps are used. The com- 

 mon value of c k is taken as 82.22.52. An inspection 

 of the table of areas in use indicates that the smallest 

 areas are very nearly as eflacient, as a rule, as the 

 greatest. — {Proc. navalinst.,ix.SOS.) R. n. t. [413 



Protection of iron from rust. — As it h.as been 

 observed that iron embedded in lime-mortar is hin- 

 dered from rusting, Riegelmann of Hanau uses a 

 paint containing caustic alkaline earth (baryta, stron- 

 tia, etc.), so that the iron may be protected as it is by 

 lime. The Neueste erfindung states that a. mixture 



