SCIENCE IN RELATION TO THE ARTS. 219 



The tensile strength of steel, as is well known, is the result of an 

 admixture of carbon with the iron, varying between one tenth and two 

 per cent, and the nature of this combination of carbon with iron is a 

 matter of great interest both from a theoretical and practical point of 

 view. It could not be a chemical compound which would necessitate 

 a definite proportion, nor could a mere dissolution of the one in the 

 other exercise such remarkable influence upon the strength and hard- 

 ness of the resulting metal. A recent investigation by Mr. Abel has 

 thrown considerable light upon this question. A definite carbide of 

 iron is formed, it appears, soluble at high temperatures in iron, but 

 separating upon cooling the steel gradually, and influencing only to a 

 moderate degree the physical properties of the metal as a whole. In 

 cooling rapidly there is no time for the carbide to separate from the 

 iron, and the metal is thus rendered both hard and brittle. Cooling 

 the metal gradually, under the influence of great compressive force, ap- 

 pears to have a similar effect to rapid cooling in preventing the sep- 

 aration of the carbide from the metal, with this difference, that the 

 effect is more equal throughout the mass, and that more uniform tem- 

 per is likely to result. 



When the British Association met at Southampton on a former 

 occasion, Schonbein announced to the world his discovery of gun-cot- 

 ton. This discovery has led the way to many valuable researches on 

 explosives generally, in which Mr. Abel has taken a leading part. Re- 

 cent investigations by him, in connection with Captain Noble, upon 

 the explosive action of gun-cotton and gunpowder confined in a strong 

 chamber, which have not yet been published, deserve particular atten- 

 tion. They show that while by the method of investigation pursued 

 about twenty years ago by Karolye (of exploding gunpowder in very 

 small charges in shells confined within a large shell partially exhausted 

 of air) the composition of the gaseous products was found to be com- 

 plicated and liable to variation, the chemical metamorphosis which 

 gun-cotton sustains, when exploded under conditions such as obtain in 

 its practical application, is simple and very uniform. Among other 

 interesting points noticed in this direction was the fact that, as in the 

 case of gunpowder, the proportion of carbonic acid increases, while 

 that of carbonic oxide diminshes with the density of the charge. The 

 explosion of gun-cotton, whether in the form of wool or loosely spun 

 thread, or in the packed compressed form devised by Abel, furnished 

 practically the same results if fired under pressure, that is, under 

 strong confinement the conditions being favorable to the full devel- 

 opment of its explosive force ; but some marked differences in the 

 composition of the products of metamorphosis were observed when 

 gun-cotton was fired by detonation. "With regard to the tension ex- 

 erted by the products of explosion, some interesting points were ob- 

 served, which introduce very considerable difficulties into the investi- 

 gation of the action of fired gun-cotton. Thus, whereas no marked 



