די

t

electricity in the ratios of their relative vo zinc, and cadmium.

"B. Metals which, when alloyed with ea

a metal of class A, do not conduct electricity their relative volumes, but always in a lowe

that calculated from the mean of their volum antimony, platinum, palladium, iron, aluminium, silver, etc.

-lead,

er, or w

"The curves representing the conductivity of diff series of alloys have the relation shown in the accompa diagrams.

"Group I. Those belonging to the alloys of met class A are almost straight lines. That of lead-tin all given as a type, Fig. 1.

Group II. The curves of alloys of metals in cla show a rapid decrement on both sides of the curve turning points being connected together by nearly st

ath,

ber,

lines. That of gold-silver alloys is given as the Fig. 2.

Group III. The curves of alloys of metals in c with those in class B show a rapid decrement on th beginning with the metal belonging to class B, then t and going in a straight line to the other side, beginning metal belonging to class A. That of tin-copper all given as the type, Fig. 3.

"In regard to alloys of the first group, if they mechanical mixtures, the metals composing them, their specific gravities were the same, would separat two layers when melted and slowly cooled, as in the lead-zinc alloys. But the alloys of lead and tin, for exa

do not separate in the same way as lead over, homogeneous wires could not be obta if these alloys were mechanical mixtures; same alloy have been proved to have the power, whether taken from the press at end of the operation.

"On the other hand, the agreement be retic and actual conductivity of these al between the calculated and actual percenta conductivity between 0° and 100° C., indic solid state, they are not chemical compound these particulars, the following law has been for all alloys of the first and second grou some of those belonging to the third group :

"The actual percentage decrement in con 0° and 100° C. is to the calculated decremen is to the calculated conductivity.

66

Among the alloys of the second grou regarded as mechanical mixtures. Silver a and well stirred together separate when s that the mass contains different amounts of different parts. But these alloys are except alloys of this group may be regarded as solid allotropic modifications of the metals in each

"In the third group of alloys, the rapid d conductivity of those alloys of the severa contain but very small amounts of a metal be A, cannot be ascribed to the existence of chen of the metals. For, in the first place, the an the metals in the alloys corresponding to the of the curves representing the conductivity too small, as will be seen by the following in

"Again, the great similarity of the curves representing conductivity of the series of alloys belonging to this g is opposed to the existence of chemical compounds in solid alloys.

"The influence exercised upon the conductivity of m by the presence of small quantities of other metals, does appear to be in any way determined by the alteratio crystalline form, or tendency to crystallise, which are kı to be influenced by that circumstance.

"If it be assumed that the metals belonging to cla undergo a molecular change when alloyed with one ano or with metals belonging to class A, and that in each an allotropic condition is induced by a small amount of metals, varying with the different metals, then many of phenomena characteristic of alloys may be explained. the curve representing the conductivity of zinc-copper a has the same form as those of other alloys, belonging t same group, and the percentage decrement in their ductivity between 0° and 100° C. is exactly what is indi by the law above stated. Hence it may be inferred solid alloys of zinc and copper are only solidified solution zinc, and of allotropic copper in each other. The diff action of reagents upon alloys, and upon the metals stituting them, when in an isolated state, may als referred to the existence of such allotropic modifica when they are alloyed, as well as to the existence of cher compounds of the metals.” 1

SLAGS, FLUXES, AND REFRACTORY MATERIALS § 15. Slags. The slags formed in metallurgical operat are, with few exceptions, produced by the union of silica metallic oxides, and termed silicates. Silicates may divided into two classes, viz. "hydrated," which con water; and "anhydrous," which are free from water. silicates produced by heat in metallurgical operations be

1 Watt's Diction. of Chem. vol. iii. pp. 943, 944.

E

to the latter class. The bases most oft from smelting ores are:-lime, magnesia, alumina. Both the silica and bases are earthy matter of the ore, the ashes of the the material of which the furnaces or vesse In melting and mixing base metals to for these elements oxidise and pass into the sla the chief bases when united with silica, o stances.

The silicates most frequently produced a iron base, of which the most fusible is 2 FeO. SiO2. The protosilicate of manga have about the same fusing point as the pro it has an olive-green colour, is opaque, crystalline. It does not absorb oxygen in like the silicates of iron, and cannot theref as an oxidising agent. A double or mult taining two or more bases is often more fusi silicate; hence a compound silicate of lime, m etc., is more fusible than either of these alone with silica, and melts readily when Likewise, oxide of manganese augments earthy silicates.

Oxide of zinc forms single silicates, whic infusible, and, as a general rule, this oxide fusibility of silicates of iron, lime, etc. I augments the fusibility of multiple silicates. bi-silicates of copper melt easily; they augme of earthy silicates. Oxide of copper is e especially in the presence of sulphur or arse it forms regulus or speise respectively. Th and bismuth are, next to the alkalies, the mos Silicates of lead melt at a red heat. Oxide the fusibility of multiple silicates, but it is ea the presence of metallic iron.

Slags are either vitreous or stony, and n they are more or less crystalline. Rapid c