Page:The American Cyclopædia (1879) Volume IX.djvu/386

 372 IRON 8teel in the process of manufacture, and ap- pear to modify its properties materially. Prof. Graham (" Chemical Journal," vol. v., 1867), in his investigations on the occlusion of gases in metals, found that wrought iron con- tained many times its own bulk of gas, nota- bly carbonic oxide. Mr. John Parry, of the Ebbw Vale iron works, Wales, has studied the subject more closely, and found that all iron contains occluded gas. In his experi- ments the amount of gas evolved was not determined, but its composition is as follows : KINDS. Carb. oxide. Carb. acid. Hydrogen. Nitrogen. Pig iron: Bpiegeleisen. . . . White iron Gray iron Wrought iron Soft ateel 17-870 2-820 5-200 84-262 24-852 0-942 8-800 1-600 9-920 16-550 81-106 84-000 89-700 64-100 52-610 6 : 8S6 8-250 1-718 6-488 The amount of hydrogen that gray pig iron is capable of absorbing when heated in an at- mosphere of this gas has been found by Par- ry to be 20 times its volume. By increasing the heat the gas thus absorbed is given off. Of the effect of gases on the physical prop- erties of iron nothing is known, and the part they play in the various manufacturing pro- cesses is only beginning to be investigated. (See IHON MANUFACTURE.) Compounds of iron with potassium, aluminum, manganese, nickel, lead, antimony, tin, and copper are known; but none of them have found important appli- cation in the arts, except ferro-manganese, which is often used instead of spiegeleisen in the Bessemer and Martin processes. It con- tains sometimes over 40 per cent of manga- nese, with a very small amount of carbon, is acknowledged to give better results than spie- geleisen, and would supersede the latter but for its cost. Strength of Iron. The strength of cast and wrought iron varies through wide limits. Cast iron is inferior to wrought iron in strength when exposed to tensile, torsional, or transverse strain, but shows a very high re- sistance to compression. Owing to its rigidity, it stretches but slightly under stress, while wrought iron elongates considerably. In esti- mating tensile strength, therefore, regard must be had to the fractured as well as to the origi- nal area. The softest and purest irons elon- gate most, and consequently show a low ten- sile strength when referred to the original area, but a high degree of resistance when re- ferred to the fractured section. A gradual in- crease in the amount of extension under strain is noticed from cast iron through steel to the softest wrought iron. The following tables, compiled from the experimental results of Hodgkinson, Fairbairn, Kirkaldy, Thal6n, Rod- man, and others, show the limits of strength of cast and wrought iron and steel under dif- ferent conditions and treatment. (Steel is in- cluded here to facilitate comparison. For more detailed information with regard to this substance, see STEEL.) Tensile and compresaive- Strength of ' rari&u* descriptions of English Cast Iron, (llodf/kimon.) KINDS. Tensile itrutigth per tq. ID. Crushing weight in tons per sq. in. Lbs. Tons. 12,694= 6-667 35,458= 6-901 16.125= 7-198 17,807= 7-949 28,468=10-477 18.988= 6-222 10,7-24= 7-466 14,426= 6-440 15,508= 6-928 13,952= 6-228 18,848= 6-959 Height of tin. 28-809 44-430 41-459 49-108 47-KJ5 40-562 52-502 88-399 83 -988 87-281 84-430 specimen, Uiii. 25-198 41-219 89-C16 45-M9 46-821 85'8C4 45-717 88-764 84-356 85-115 88-646 Clyde, No. 1 " "2 " " 2 " " 8. Yniscedwyr, No. 1 .... Anthracite, No. 2 The tensile strength of Austrian gun iron is from 30,000 to 38,000 Ibs. ; of Russian, about 27,000 Ibs. ; and of Swedish, about 34,000 Ibs. Experiments made by Capt. Rodman of the United States ordnance corps, with Green- wood, Springfield, and Salisbury pig irons (charcoal), and mixtures of the same, showed in 16 determinations a minimum specific grav- ity of 7'099 and a maximum of 7'307 ; a min- imum tensile strength of 22,179 Ibs. and a maximum of 42,884 Ibs. to the square inch. The following determinations of the strength of Richmond (Mass.) charcoal pig were made at the South Boston foundery. This iron is smelted from pure red hematite, with temper- ature of blast varying from 100 to 350 F., and is largely used for ordnance : Specific gravity. Tensile strength, in Ibs. rer sq. in. A B C A B C No. 1. u 2. " 8. " 4. 7-0820 7-1220 7-1890 7-2649 7-0858 7-1252 7-1796 7-2983 7-0809 7-0797 7-1750 7-2125 14,879 16.898 16.844 25,188 16,688 19,781 23,119 29,066 16,618 18.471 19.&8T 24,726 Remelting in a reverberatory furnace raised the average specific gravity of this iron to 7'3135, and the average tensile strength to 40,022 Ibs. per square inch. Fairbairn has de- termined the transverse strength of cast iron rectangular bars from nearly all the British iron works. In 51 experiments on all shades of gray pig iron, the minimum breaking weight for bars 4 ft. 6 in. between supports was 357 Ibs. to the square inch, corresponding to a specific gravity of 6-916, and the maximum 581 Ibs., corresponding to a specific gravity of 7'122. Irons intermediate in strength, how- ever, often show a higher specific gravity. From experiments made by Fairbairn to deter- mine the effect of hot blast on the strength of pig iron, he concluded that No. 1 irons had been deteriorated, No. 2 slightly injured by it, and No. 3 improved by the use of hot blast. According to experiments on the resistance to torsion in cast iron, the length of the bar submitted to torsion being about eight diame- ters, the ultimate strength of seven samples varied from 6,176 to 10,467 Ibs. to the square