466 



SCIENCE 



[N. S. Vol,. II. No. 41. 



purification and the utilization of sewage 

 occupied the attention of the British Asso- 

 ciation as early as 1864, and between 1869 

 and 1876 a committee of the Association 

 made a series of valuable reports on the 

 subject. It was not till the chemist called 

 to his aid the biologist, and came to the 

 help of the engineer, that a scientific sys- 

 tem of sewage purification was evolved. 



Dr. Frankland many years ago suggested 

 the intermittent filtration of sewage; and 

 Mr. Baldwin Latham was one of the first 

 engineers to adopt it. But the valuable ex- 

 periments made in recent years by the State 

 Board of Health in Massachusetts have 

 more clearly explained to us how by this 

 system we may utilize micro-organisms to 

 convert organic impuritj' in sewage into 

 food fitted for higher forms of life. To 

 effect this we require, in the first place, a 

 filter of any material which affords numer- 

 ous surfaces or open pores. Secondly, that 

 after a volume of sewage has passed through 

 the filter an interval of time be allowed, in 

 which the air necessary to support the life 

 of the micro-organisms is enabled to enter 

 the pores of the filter. Thus this system 

 is dependent upon oxygen and time. Under 

 such conditions the organisms necessary for 

 purification are sure to establish themselves 

 in the filter before it has been long in use. 



In other branches of civil and mechani- 

 cal engineering the reports in 1831 and 

 1832 on the state of this science show that 

 the theoretical and practical knowledge of 

 the strength of timber had obtauied con- 

 siderable development. But in 1830, be- 

 fore the introduction of railwaj'S, cast iron 

 had been sparingly used in arched bridges 

 for spans of from 160 to 200 feet, and 

 wrought iron had only been applied to 

 large -span iron bridges on the suspension 

 principle, the most notable instance of 

 which was the Menai suspension bridge, by 

 Telford. 



The development of the iron industry is 



due to the association of the chemist with 

 the engineer. The introduction of the hot 

 blast bj' Neilson, in 1829, in the manufac- 

 ture of cast iron had effected a large saving 

 of fuel. But the chemical conditions which 

 affect the strength and other qualities of 

 iron, and its combination with carbon, sili- 

 con, phosphorus and other substances had 

 at that time scarcely been investigated. In 

 1856 Bessemer brought before the British 

 Association at Cheltenham his brilliant 

 discovery for making steel direct from the 

 blast furnace. This discoveiy, followed by 

 Siemens's regenerative furnace, by Whit- 

 worth's compressed steel, and by the use of 

 alloys and by other improvements too 

 numerous to mention here, has revolu- 

 tionized the conditions under which metals 

 are applied to engineering purposes. 



Indeed, few questions are of greater in- 

 terest, or possess more industrial impor- 

 tance, than those connected with metallic 

 alloys. This is especially true of those al- 

 loys which contain the rarer metals ; and 

 the extraordinaiy effects of small quanti- 

 ties of chromium, nickel, tungsten and 

 titanium on certain varieties of st«el have 

 exerted profound influence on the manu- 

 facture of projectiles and on the construc- 

 tion of our armored ships. Of late years 

 investigations on the properties and struc- 

 ture of alloys have been numerous, and 

 among the more noteworthj' researches 

 may be mentioned those of Dewar and 

 Fleming on the distinctive behavior, as re- 

 gards the thermo-electric powers and elec- 

 trical resistance, of metals and alloys at 

 the very low temperatures which may be 

 obtained bj' the use of liquid air. 



Professor Eobei-ts -Austen, on the other 

 hand, has carefullj' studied the behavior of 

 alloys at verj' high temperatures, and by 

 employing his delicate pyrometer has ob- 

 tained photographic curves which aflbrd 

 additional evidence as to the existence of 

 allotropic modifications of metals, and which 



