494 



MECHANICAL IMPROVEMENTS. 



practice of his profession, which he continued 

 until 1868, when he was elected to Congress. 

 He was reelected in 1870, 1872, and 1874, but 

 was not a candidate in 1876. At different 

 times during his congressional career he was 

 chairman of the Committee on Elections and 

 of that on Railways and Canals, and he served 

 on the Committees on Naval Affairs, Revision of 

 Laws, and the Judiciary. OnDecember 7, 1876, 

 Mr. McCrary introduced into the House the 

 bill which was the first step in the legislation 

 for creating the Electoral Commission. The 

 resolution, which provided for a joint commit- 

 tee of Congress to consider the mode of count- 

 ing the electoral vote, was referred to the Judi- 

 ciary Committee, of which he waw a member. It 

 was passed, and Mr. McCrary became a member 

 of the joint committee on the part of the House. 

 He advocated the Electoral bill, and appeared 

 before the Electoral Tribunal. He was one of 

 the first to support the Republican position in 

 the Florida case, and argued against the power 

 of Congress to go behind the returns. When 

 President Hayes formed his cabinet, Mr. Mc- 

 Crary was chosen as Secretary of War. He is 

 the author of a work recently published on the 

 " Law of Elections." 



MECHANICAL IMPROVEMENTS AND 

 INVENTIONS. There has not been any re- 

 markable event to chronicle in the history of 

 mechanical engineering for the past year. No 

 year passes, however, without many improve- 

 ments and inventions, and a steady progress 

 in the understanding of mechanical principles, 

 and new victories over the forces of Nature. 

 No art or science can show more plainly a prog- 

 ress from year to year ; no art can chronicle 

 more certain, conspicuous, and important an- 

 nual advances than mechanical engineering. 

 Considerable attention is being paid in Europe 

 to the various forms of continuous brakes, 

 and careful experiments have been made with 

 them. There has been much debate as to the 

 relative merits of the English and American 

 types of railroad engine. The English engine, 

 with a rigid wheel-base, in which the entire 

 dead-weight is supported by the driving-wheels, 

 is, no doubt, much more economical on such 

 straight and level roads as are found in Eng- 

 land, and in some parts of the Continent ; but 

 in no other part of the world is it adapted to 

 the railroads as they are now laid ; and as the 

 American bogie engine, of flexible wheel-base, 

 has supplanted the other form in Canada, and 

 other British colonies, and is now preferred 

 in Russia, so will it probably be found pref- 

 erable in India, and all countries where en- 

 gineering works cannot be as thoroughly made 

 as in England. The progress made in ma- 

 chine puddling is not rapid, and the attention 

 of iron-masters is more taken up with the prog- 

 ress in the manufacture of steel, or steel-pro- 

 cess iron, which may yet entirely supplant pud- 

 dled iron. 



The study which has been given to the 

 steam-engine of late years is leading to a bet- 



ter knowledge of the true properties and ac- 

 tion of steam. Isherwood first pointed out 

 that the limit to the economy of fuel by the 

 application of the principle of expansion was 

 soon reached. The Gallatin experiments 

 proved that considerable loss resulted from a 

 measure of expansion as great as 10 to 1. 

 The construction of boilers which preserve 

 the steam from condensation is the aim now 

 of engineers, and this end is best subserved by 

 the use of jackets of a proper kind, and cylin- 

 ders with the thinnest possible walls, and by a 

 double set of ports for the ingress and escape 

 of steam. The advantages of steam-jacketing, 

 which was invented by Watt, have been of 

 late rejected in favor of the illimitable bene- 

 fits which were hoped for from working steam 

 expansively, and for the greater work which 

 it was supposed could be obtained from high 

 pressure. Recent experiments show that the 

 economy in properly steam-jacketing the cylin- 

 der is very great, that the same work can be 

 attained under a much lower head of steam, 

 by preventing condensation and keeping the 

 interior of the cylinder dry, and by perfecting 

 and increasing the vacuum. The jacket is 

 most efficient when the cylinder walls are the 

 thinnest, and is almost useless when they are 

 as thick as they often are, and when the cylin- 

 der covers are not included in the jacket. 

 Him, experimenting with a vertical cylinder 

 engine, found that under the same pressure, 

 and the same measure of expansion, the ste.'.m- 

 filled jacket gave 23.5 per cent, more power ; 

 and he calculated the actual economy at 22.2 

 per cent Hallauer, with duplicate Corliss en- 

 gines, at Mulhouse, found an economy in the 

 weight of steam consumed per hour per total 

 horse-power of 23.75 per cent. ; and Lelou- 

 tre, in recent experiments under various con- 

 ditions, at the same place, reports an economy 

 of 15 to 25 per cent, in favor of steam-jacket- 

 ing. M. Cornut, an eminent French engineer, 

 reports, as the result of a careful trial, that a 

 saving of 15 to 20 per cent, can be obtained 

 by the employment of a well-constructed 

 jacket, receiving its steam direct from the 

 boiler, when the steam is cut off at to -j^ of 

 the stroke from the beginning. 



The Belgian commissioners for the in- 

 spection of boilers ascribe interior corrosion, 

 which appears in small separated circular holes, 

 often near the centre of an otherwise perfect 

 plate, to the presence in the feed-water of 

 chlorides or alkaline salts, and not to acids in 

 the water. External corrosion, which is one 

 of the principal elements in the decay of boiler 

 walls, they declare to be caused by the deposit 

 on the plates of soot impregnated with sulphu- 

 ric acid ; the soot adheres only to damp por- 

 tions of the plates. 



The report of the Special Committee of the 

 United States Board of Supervising Inspectors 

 of Steam Vessels, in a series of experiments 

 made in September, 1875, on the principal 

 forms of safety-valve in use, shows that under 



