1817.) On the Decomposition of the Earths. 91 
This expedient consists in nothing more than in having ascreen 
made of deal planks, which are 1+ inch thick, and reach about 12 
feet from the floor of the laboratory. It is so constructed that one 
half of it opens like a door; the other half remaining fixed. The 
blow-pipe is placed behind the half that is fixed ; anda small hole 
is bored through this half, which is barely large enough to allow the 
jet and stop-cock to pass throagh. By means of the door, the 
operator has, at all times, access to the piston for compressing the 
gas ; and when this door is closed, the gas may be ignited without 
a possibility of danger. If an explosion happen, the screen protects 
the operator. This screen may be also placed before a window; if 
its height and situation be such as to secure persons without from 
any consequences of an explosion; and in this case, as the force of 
the explosion acts generally in the opposite direction to that of the 
flame, any part of the copper box which may be driven off will 
escape without repercussion. 
The drawing which accompanies this will show the situation of 
the gaseous reservoir of the blow-pipe before the door of the screen 
is closed upon it. (See the Plate,) 
AB is the deal screen, in two parts;.A being made to open; 
and B a fixture; before the window, C. 
D represents the gaseous reservoir of the blow-pipe. 
E the bladder containing the gaseous mixture for compression. 
¥ the hand of the operator upon the stop-cock of the jet, on 
the outside of the screen. 
GH a tube of glass, or of brass, for the jet. 
I the spirit lamp for igniting the gas. 
The great advantage of this screen over the plan of having cases, 
or covers, for the blow-pipe, is this; that the experiments are not 
interrupted or delayed by the necessity of removing from the appa- 
ratus the bladder and piston~every time that a fresh supply of the 
gaseous mixture has been compressed into the reservoir. All that is 
required, previously to condensing the gas, is to open the door; 
and, previously to its ignition, to close the same, asa security from 
danger, . 
In this manner, as I have before stated, I have been enabled to 
continue my experiments. The new results, which I have obtained, 
will perhaps interest your readers; and, consistently with my former 
communication, t will endeavour to state them with as much brevity 
as the nature of the subject will admit. 
* Further Experiments with the ignited Gas. 
_ A. Sand Tubes of Drigg, in Cumberlund.—This experiment was 
made at the suggestion of H. Warburton, Esq. I had maintained 
in my Lectures, before the University, that the substance investing 
the interior of these tubes was not a vitrified hody, bat a siliceous 
concretion analogous to hyalile or pearl-sinter. ‘The result of its 
exposure to the ignited gas has confirmed me in this opinion. Its 
fusion was instantaneous; and similar to. the fusion of hyalite ; 
leaving a bead of pure limpid glass; containing bubbles; like rack 
crystal after fusion, 
