746 REPORT—1896. 
The following Papers and Reports were read :— 
1. On Reflected Waves in the Explosion of Gases. 
By Professor H. B. Dixon, E. H. Strance, and E, Granam. 
The authors exhibited some photographs which show the return sound-wave 
produced by the explosion-wave in gases when it reaches the end of the tube. The 
gases were fired in a thick glass tube closed by a steel plug. The flash was photo- 
graphed on a very rapidly moving film. By measuring the velocity of these 
sound-waves the authors estimate the maximum temperature of the gases immedi- 
ately in the wake of the explosion-wave. The maximum temperatures lie between 
3,000° and 4,000°C. They are thus of the same order as those given by Bunsen, by 
Berthetot,and by Mallard and Le Chatelier for the temperature of the explosion itself. 
2. The Action of Metals and their Salts on Ordinary and on Réntgen 
Rays: a Contrast. By Dr. J. H. Guapstone and W. H1ssert. 
This paper is an extension of previous work on the special properties of metals 
and salts, and may be considered as an application of Réntgen rays to chemical 
research. 
In regard to the rays of ordinary light solid metals absorb them completely, 
and are therefore opaque. If, however, the metals combine with an electro- 
negative radicle, they lose their power of absorbing light, except a few which show 
the phenomena of selective absorption. Solutions of salts resemble the crystallised 
solid in their action on light. 
With regard to Réntgen rays, on the contrary, metals exhibit every degree of 
opacity or transparency, from lithium—which is practically non-absorptive—to 
such metals as gold and platinum, which are practically opaque. The salts of 
these metals are not transparent, but the metal in them seems to have the same 
effect on the Réntgen rays as in the uncombined condition. This seems to be 
equally true when the salts are dissolved in water. 
The order of absorption follows that of atomic weight, as found by Barrett and 
others, not that of density or combining proportion. The absorption of the 
Rontgen rays by a salt solution appears to be that of both constituents of the salt 
added together plus that of the solvent. 
The work was principally carried on in the laboratory of the Polytechnic, 
Regent Street, London. Photographs were exhibited. 
3. Limiting Explosive Proportions of Acetylene and Detection and Measure- 
ment of the Gas in the Air. By Professor Frank Crowes, D.Sc. 
(Lond.) 
The value of acetylene as an illuminant and the discovery of its ready pro- 
duction from calcium carbide have led to the manufacture of this gas in some 
quantity, and acetylene will probably be dealt with in still larger volume in the 
near future. It becomes, therefore, important to devise methods of detecting its 
presence in the air, arising from leakage and escape, and to measure the percentage 
of the gas present at any place. It is also important to ascertain what proportions 
of the gas, when present in mixture with air, will lead to explosion if the mixture 
should be kindled. 
The Detection of Small Proportions of the Gas will not be readily effected by 
its smell when it is prepared in a state of purity; at present the smell is made 
much more pronounced by the impurities which the commercial gas contains. 
Further, the smell will not in any case furnish a means of measuring the pro- 
portion present in the air. The method. applied by the writer to the detection 
and measurement of five-damp and coal-gas in the air, however, serves for 
detecting and measuring acetylene as well. A small hydrogen flame jet to 
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