ON THE CRYSTALLINE SLAGS. 371 
An attempt was made to measure approximately the 
acute angle of the rhomb in the following manner :— fn 
_ By means of a stout branch with an universal joint like 
that of Wollaston’s goniometer, the slag was attached 
to a common six-inch circular protractor graduated to A B 
half degrees, with its plane surface upwards, and parallel 
to the plane of the protractor. The protractor was 
placed upon a table, having traced upon it a fine straight 
line longer than the diameter of the protractor. A com- 
pound microscope, having a spider line in the focus of 
the eye-piece, was firmly fixed with its axis perpendi- 
cular to the table, and at such a distance from it as to 
command distinct vision of the plane surface of the 
slag. By moving the protractor with the slag attached to it till the images 
of the sides of the rhomb formed in the microscope successively coincided 
with the spider line, and reading off the degrees and minutes at which the 
protractor met the line traced on the table, the angle is obtained through 
which the protractor has been turned between the two observations; or, the 
angle of the rhomb. The values of the angle ACB thus observed were,— 
77°-0, 79° 45', 81° 30’, 80°, 78° 15', 79° 15’, 77° 45', 78° 20', 82° 6’, 80° 50’, 
77° 30', 80°, 80° 15’. Such a method of observation is obviously insuffi- 
cient for the identification of a crystalline species; yet renders it probable 
that these crystals are the same as No. 13, a section of which, by aplane 
perpendicular to £', would produce a rhomb of 81° 36’. 
At 181 C. specific gravity of slag = 3°9984, 
We conclude our present report by the cry- Crystal in profile. 
stallographic description of an interesting slag 
obtained from the gold and silver refinery of 
Messrs. Betts of Birmingham. The matrix is 
very heavy, and probably differs considerably in 
composition from the minute crystals in question, 
which appear to be, as it were, sublimed upon the 
surface, and of which it is impossible to obtain 
sufficient for analysis. mW /m 
The surface of this is studded with numerous 
extremely small black bright crystals belonging End of crystal. | m' | m 
Cee rr ea ee eR 
all 
= 
-to the oblique prismatic system. The angles 
between normals to the faces are mm! 73° 10’, 
pp! 86°, mp 29° 42’. The edge in which pp! 
intersect makes an angle of nearly 46° 30! with 
the intersection of m,m!*. For a portion of the 
slag having crystals adhering to it, at 19%1 C. 
specific gravity of slag = 6°3802. 
We have remaining an extensive series of slags from various metallurgical 
works, which we have not yet had time to investigate, but we hope to be able 
to continue our labours in this department, and to present to the Association 
a second report at no distant period. We have several specimens of beauti- 
fully crystallized octahedral or magnetic oxide of iron, and many other 
erystals from the copper furnaces. We take this opportunity of publicly 
thanking those gentlemen who have obligingly contributed to our collection, 
and of inviting any others, who may have the opportunity, to further our 
views in a similar manner by the contribution of specimens. 
* I cannot find any mineral having the same or nearly the same angles.—W. H. M, 
