236 Transactions of the Royal Microscopical Society. 
IIl.—Microscopic Aspects of Krupp’s Silicate Cotton. 
By H. J. Stack, F.G.8., Sec. R.M.S. 
(Read before the Royau Microscoricat Soctery, April 4, 1877.) 
Pratrs CLXXX. anp CLXXXI. | 
SizicaTE cotton is the name under which blast-furnace slag 
reduced to a fibrous condition is now sold as a non-conducting 
substance for covering steam boilers, pipes, ice-houses, safes, &e. 
It is manufactured at the works of Herr Krupp, at Sayn, in 
Germany, by forcing a blast of steam, water, or air through 
molten slag, in the viscous state in which it runs from the furnace. 
Having obtained a specimen through the kindness of Messrs. 
Jones, Dade, and Co., the English agents, it was found when lightly 
compressed to be much like cotton wool, but of finer fibre. 
Amongst the fibres are to be seen a number of bulbs of various 
forms and sizes, seldom, however, exceeding the magnitude of an 
ordinary pin’s head, and usually less. The fibres vary in thick- 
ness from that of common spun glass to an extreme tenuity repre- 
sented by fractions of a thousandth of an inch. They are easily 
blown about as a fine dust, and from their material, and forms, 
as shown in some of the sketches, Figs. 1 to 4, must be very mis- 
chievous if introduced into the lungs. It is said that special pre- 
cautions have to be taken to prevent workmen engaged in the 
manufacture from being seriously, or fatally, injured. 
- The bulbs present some interesting appearances. They vary in 
shape and size as Figs. 5 to 17 show, and also in internal structure, 
though they may be generally described as solid bodies containing 
more or less numerous vesicles and hollows. 
Considering the sudden and violent explosive action by which 
they are formed, little regularity might be expected in their 
markings, but a considerable number exhibit a very beautiful 
and symmetrical ornamentation. A spherule, for example, one- 
thirtieth of an inch in diameter is thickly covered with compound 
vesicles (see Fig. 18), consisting of a central clear glass film sur- 
rounded by numerous minute bubbles, the whole when lit up under 
the microscope having an elegant jewelled appearance. 
When broken, the bulbs exhibit a conchoidal fracture diversified 
with small cavities and vesicles. In some cases the symmetrical 
arrangement last mentioned is found in the vesicles occupying the 
centre of a bulb. In some spherules obtained from a Yorkshire 
furnace by Mr. Sorby, numerous groups of crystals could be seen 
composed of minute prisms arranged in rectangular patterns. 
To test the mode in which such regular patterns as in Fig. 18 
could be formed by explosive action upon a viscous substance, an 
