162 Scientific Intelligence. [Fex. 
VII. Improvement in the Oxygen and Hydrogen Blow-pipe. By 
Dr. Clarke. 
(To Dr. Thomson.) 
DEAR SIR, 
It may concern your chemical readers to be informed that, by an 
improvement which I have made in the mode of using the gaseous 
blow-pipe, for burning compressed hydrogen and oxygen, I have 
been able to add greatly to its power of fusion; and have removed 
an obstacle which has occasioned failure, in some instances, for the 
reduction of the earths to the metallic state. 
Instéad of using water, in the pneumatic cylinder adapted to the 
instrument by Professor Cumming, I have used oi/; pouring in 
barely a sufficient quantity of sallad oil to cover the wire-gauze. It 
must have been obvious that the water was calculated to prevent the 
possibility of reviving the metals of the earths, in all instances 
where it was forced out of the jet, and came into contact with the 
fusing mass. ‘The oz/ on the contrary rather tends to aid the expe- 
riment: it moreover sustains a more tranquil ebullition during the 
passage of the gas. The explosions which take place occasionally 
in the cylinder do not communicate combustion either to the oz/, or 
to the gas within’ the reservoir. I caused three explosions, pur- 
posely, by suffering the gas to burn out ; but not a drop of the oil 
was driven out, and the consequences were only very slight detona- 
tions within the cylinder. The other part of the improvement con- 
sists in substituting for the brass tube a thermometer tube with a 
very large diameter; in the use of which there is no danger; but 
the volume of the flame is such that I have fused 100 grains of 
platinum into a single brilliant globule upon charcoal; and in your 
next number IJ will point out a method of extending the use of this 
apparatus to the arts and manufactures. The combustion of iron, 
with it, affords one of the most splendid and striking experiments 
that can be conceived ; causing a shower of fire. 
Cambridge, Jan. 12, 1817. Epwarp Danievt CLarKE. 
VIL. Height of Table Mountain, 
The altitude of Table Mountain, at the Cape of Good Hope, 
above the level of the sea, is 1087 yards. 
EX. Benzoic Acid as a Re-agent for Iron. 
Mr. Peschier, a skilful chemist and practitioner of pharmacy at 
Geneva, has found that the benzoic acid, and still better the alka- 
line benzoates, are very good and useful tests of the presence and 
quantity of iron contained in any solution. ‘They precipitate iron 
readily and entirely, and, being cheaper and more easily obtained | 
than the succinates, which are commonly employed for that pur- 
pose, are considered by Mr. Peschier as deserving the preference in 
chemical analysis, Another very-valuable property of benzoic acid 
