255 
ing 168 retorts working successfully with both regenerator 
systems. The introduction of machine-made retorts in the 
Belgian process is gaining ground. The Silesian process in 
Silesia, has been modified by the introduction of two rows of 
mufiles in the place of one as formerly. 
There is a tendency every where to utilize waste products. 
In Silesia, furnaces are being constructed for the sole purpose 
of working over lead slag heaps a century or more old, and 
in all metallurgical operations the tendency is to make use 
of poorer ores. Thus in Silesia they work iron ores of 18 
per cent. iron, and zine ores of 9 per cent. These ores of 
zinc are so poor that it is impossible to use the double tier of 
muffles, and yet with the regenerator system it is possible to 
treat them. . 
He also made some remarks on False Gems and their Optical 
Characters, illustrated by means of specimens. He said that 
since the study of the optical characters of minerals has 
become so important there has been a very great demand for 
sections of minerals. There are certain minerals, such as 
Ruby and Rutile, which are not easily procured, the one be- 
cause of its use as a gem, and the other because it is so fre- 
quently twinned or fissured, that good sections for optical 
purposes are not easily obtained. A considerable number of 
very beautiful specimens have been sold in Europe during the 
past two or three years which show most of the properties of 
these minerals. Mr. Stegg, of Hombourg, first doubted them 
on account of their beauty. He noticed that certain sections 
of rutile were negative when they should be positive. This 
induced him to take one of the preparations to pieces, and he 
found that it consisted of a thin section of Calcite, covered 
with a plate of gelatine which gave it the proper color. The 
imitation in Ruby is more deceptive, since Ruby is negative. 
Mr. Stegg prepared for me, at my request, the three specimens 
exhibited, for the mineralogical cabinet of the School of Mines. 
Half of each specimen, artificial Ruby, Rutile and Mellite 
show the Calcite, the other half shows the Calcite covered 
with the colored gelatine. 
