688 Chronicles of Science. | Oct., 
not yet been made acquainted with any practical results which will 
admit of our comparing it with those which we have already described. 
Much attention has recently been given to mining-powder, with 
a view to increase its disruptive power, and produce it at a cheaper rate. 
M. Nobel states that by damping mining powder with nitroglycerine its 
explosive power is trebled, and the noise of the explosion much less 
than when ordinary powder is used. One firm is making blasting- 
powder with nitrate of soda instead of nitrate of potash, by which the 
cost is reduced one-third, but this powder has the objection of a ten- 
dency to deliquescence unless it is very. caretully kept. in another 
powder, the spent tan of the tanners’ yards is substituted for charcoal, 
and an increased activity given to the composition by the addition of 
a little chlorate of potassium. This explosive powder is said to have 
a considerable amount of disruptive power; in price it stands about 
equal to that manufactured with nitrate of soda. 
A composition for mining purposes is now being subjected to 
experimental trial in some of the mines near Tavistock, in Devonshire. 
The peculiarity of this is, that the materials which constitute it are 
kept apart, or at least in two parcels, neither of which are in them- 
selves explosive. They become so, however, on being mixed in certain 
defined proportions, which is not done until the moment of its being 
placed in the holes. The actual composition of this explosive agent is 
not stated, but it must of necessity consist of carbonaceous matter in 
one parcel, and of some agent which rapidly developes oxygen—as 
nitre or chlorate of potassium — in the other. At the request of 
Lord Kinnaird, the chairman of the Mines Commission, a series of 
experiments has been made in Dolcoath and some other mines with 
gun-cotton, as manufactured by the Austridn process. The results 
were satisfactory as regarded its explosive power and the absence of 
visible smoke. Dr. Angus Smith and Dr. Bernays are engaged in the 
analysis of the air collected in the mines before and after the explo- 
sions. The report of the Commission will contain these analyses, and 
much special information on the use of gun-cotton in mines. Mr. John 
Scott Russell’s paper on “ Gun-cotton,” in the last number of ‘ The 
Journal of Science,’ contains all the most recent information on this 
explosive compound. 
MINERALOGY. 
W. C. Bischoff* has shown that the basic silicates of alumina are 
more refractory than the acid silicates. Alumina artificially obtained 
and chemically pure, is less refractory than chemically pure silica ; 
but natural alumina is more refractory than natural silica as found in 
quartz rock-crystal and amethyst. Herr Bischoff has also discovered 
that the mineral pyrolusite may probably be found to be a new source 
of the rare metal thallium, a specimen in his collection giving 1 per 
cent. of this new element. 
H. Haidinger has communicatedt to the Académie Impériale des 
* «Journal d’Erdmann et Werther.’ ‘ Annales de Chimie.’ 
t+ ‘Ann. der Chem. und Pharm,’ vol. exxix. p. 375. 
