Microscopie Aspects of Silicate Cotton. By H. J. Slack. 237 
ounce or two of common rosin was melted in an iron ladle, and 
when it began to boil suddenly thrown into cold water. An 
irregular brittle mass was obtained, exhibiting here and there 
small white patches. These when examined with 3-inch power 
showed some compound vesicles like Fig. 18, and others as it were 
in process of formation. It seemed as if the first action of the 
explosive steam was to produce an immense number of minute 
vesicles, and that those in the centre had a greater tendency to 
coalesce than those at the margin. Some centres were composed of 
a single clear vesicle, others of two, three, and so on. 
The general character of the silica cotton threads is much like 
the volcanic product known as “ Pele’s hair”; the bulbs resemble 
volcanic bombs. 
In some specimens the bulbs are like common white glass; in 
others they glow with the iridescent tints of Venetian work, and 
constitute objects of considerable beauty when illuminated with a 
side silver reflector. 
Iron slags producing this material are compounds of silica, 
alumina, &c. 
The following analysis from Percy’s ‘ Metallurgy’ may be taken 
as an illustration of their composition. The specimen was from 
South Staffordshire, and crystallized in well-defined translucent 
square prisms * : 
SHUIET ip? ok se eG pp ede ce LCOS 
NOMINARy Osho. so ssha- sl) Gaee sce LAUT 
IDTTIREN Rod as) Soles ote gas eo orl! 
Miatonesine gag cas ea as se ea RSG 
Protoxide of manganese .. .. .. 0°40 
Protoxide of iron Se 0 ee as) ICH 
Potash@ «as. tee a Ga ee Se OSD 
Sulphide ofcaleium.. .. .. .. 0°82 
99°81 
The spun glass condition of slag is mentioned by Percy, who 
says,t “owing to some accidental condition the melted slag has 
actually been spun as it were by the blast, just as glass is spun by 
a wheel. I have received beautiful specimens of this kind from my 
friend Mr. Levick of the Blaina and Cwm Celyn Iron Works, and 
also from Prussia.” 
The fine threads of silicate cotton fuse readily into beads in 
the flame of a spirit lamp, but they are unchanged by a full red 
heat. 
The substance is not a pleasant one to handle, and no doubt 
numbers of sharp, and often curved and barbed particles entering the 
skin would produce great irritation. On this account it is supplied 
* Percy’s ‘ Metallurgy,’ vol. i. p. 23. t Ibid, p. 27. 
