786 REPORT— 1895. 



The manufacture of iron, steel, and other metals, and the formation of alloys, 

 are essentially chemical operations ; and the Bessemer and Gilchrist processes, by 

 which steel is produced in large quantities directly from cast iron, by eliminating 

 a portion of the carbon contained in it, and also the injurious impurities, silicon 

 and phosphorus, in place of the former costly and circuitous method of removing 

 the carbon from cast iron to form wrought iron, and then combining a smaller 

 proportion of carbon with the wrought iron to form steel, are based on definite 

 chemical changes, and necessitated chemical knowledge for their development. 



Chemical analysis is needed for determining the purity of a supply of water, or 

 the nature and extent of its contamination ; and Dr. Clarke's process for softening 

 hard water, by the addition of lime water, depends upon a chemical reaction. The 

 methods also of purifying water by filtration, shaliing up with scrap iron, and 

 aeration, are chemical operations on an extensive scale ; and their efficiency has to 

 be ascertained by chemical tests. 



Cements and mortars depend for their strength and tenacity, when mixed with 

 water, upon their chemical composition and the chemical changes which occur. 

 The value of Portland cement requires to be tested quite as much by a chemical 

 analysis of its component parts, as by tlie direct tensile strength of its briquettes ; 

 for an apparently strong cement may contain the elements of its own disruption, in 

 a moderate proportion of magnesia or in an excess of lime. The chemical change 

 which has been found to occur in the Portland cement of very porous concrete 

 exposed to the percolation of sea-water under considerable pressure, by the substi- 

 tution of the magnesia in sea-water for the lime in the cement, if proved to 

 take place even slowly under ordinary circumstances, would render the duration 

 of the numerous sea works constructed with Portland cement very precarious, 

 and necessitate the abandonment of this very convenient material by the maritime 

 engineer. 



Explosives, which have rendered such important services to engineers in the 

 construction of works through rock and the blasting of reefs under water, as well 

 as for purposes of attack and defence, form an important branch of chemical 

 research. The uses of gun-cotton as an explosive agent, though not for guns, have 

 been greatly extended by the investigations of Sir Frederick Abel, and by the 

 discovery that it can be detonated, when wet and unconfined, by fulminate of 

 mercury ; whilst smokeless powder, a more recent chemical discovery, seems 

 likely, by its application to firearms, to produce important modifications in the 

 conditions of warfare. The progress achieved by chemists in other forms of 

 explosives has been marked by their successive introduction for blasting in large 

 engineering works. Thus the removal of the rock in driving the Mont Cenis 

 tunnel, in 1857-71, was effected by ordinary blasting powder ; whilst the excava- 

 tion of the longer St. Gothard tunnel, in 1872-82, was accomplished by the more 

 efficient explosive dynamite.^ Moreover, the first great blast for removing the 

 portion of Hallett's Reef which obstructed the approach to New York Harbour, 

 was effected mainly by dynamite, together with vulcan powder and rendrock, in 

 1876 ; whereas the far larger Flood Rock, in mid-channel, was shattered in 1885 

 by rackarock, a mixture of potassium chlorate and nitrobenzol, and a much 

 cheaper and a more efficient explosive under water than dynamite.' Rackarock is 

 one of the series of safety explosives first investigated by Dr. Sprengel in 1870, 

 which, consisting of a solid and a liquid, is safely and easily mixed for use ; and 

 these materials, being harmless previously to their admixture, can be stored in large 

 quantities without risk.^ The cost also of this large blast was greatly reduced by 

 the sympathetic explosion of the bulk of the cartridges by the detonation of a 

 series of primary exploders, placed at intervals along the galleries and fired simul- 

 taneously by electricity from the shore. 



The utilisation of sewage belongs to agricultural chemistry ; and the deodorisa- 

 tion of sewage, and its conversion into a commercial manure, are chemical processes. 



' Proceedings Inst. C.E., vol. 95, p. 266. 



' Ihid., vol. 85, pp. 267, 270. 



' Journal of the Chemical Society, August 1873. 



