ON PYROXYLIN. 
23 
Stokes, the term fluorescence has been applied by their discoverer, and to the phenomena 
brought forward this evening at the Royal Institution, it was proposed to apply the 
term calorescence. * 
It was the discovery, more than three years ago, of a substance opaque to light, and 
almost perfectly transparent to radiant heat—a substance which cut the visible spectrum 
of the electric light sharply off at the extremity of the red, and left the ultra-red radia¬ 
tion almost untouched, that led the speaker to the foregoing results. They lay directly 
in the path of his investigation; and it was only the diversion of his attention to subjects 
of more immediate interest that prevented him from reaching, much earlier, the point 
which he has now attained. On this, however, he can found no claim; and the idea of 
rendering ultra-red rays visible, though arrived at independently, does not by right 
belong to him. The right to a scientific idea or discovery is secured by the act of publi¬ 
cation ; and, in virtue of such an act, priority of conception as regards the conversion of 
heat-rays into light-rays belongs indisputably to Dr. Akin. At the meeting of the 
British Association, assembled at Newcastle in 1863, he proposed three experiments by 
which he intended to solve this question. He afterwards became associated with an 
accomplished man of science, Mr. Griffith, of Oxford, and, jointly with him, pursued the 
inquiry. Two out of the three experiments proposed at Newcastle by Dr. Akin are im¬ 
practicable. In the third, Dr. Akin proposed to converge the rays of the sun by a 
concave mirror, to cut off the light by “proper absorbents,” and to bring platinum foil 
into the focus of invisible rays. It is quite possible, that, had he possessed the instru¬ 
mental means at the speaker’s disposal, or had he been sustained as the speaker had been 
both by the Royal Society and the Royal Institution, Dr. Akin might have been the 
first to effect the conversion of the dark heat-rays into luminous ones. For many years 
the idea of forming an intense focus of invisible rays had been perfectly clear before the 
speaker’s mind ; and in 1862 he published experiments upon the subject. The effects 
observed by him in 1862 at the focus of invisible rays were such as no previous experi¬ 
menter had witnessed, and no experimenter could have observed them without being 
driven to the results which formed the subject of the evening’s discourse. Still publica¬ 
tion is the sole test of scientific priority; and it cannot be denied that Dr. Akin was the 
first to propose definitely to change the refrangibility of the ultra-red rays of the spec¬ 
trum, by causing them to raise platinum foil to incandescence. 
ON PYROXYLIN. 
BY MM. PELOUZB AND MATJREY. 
The attempts made during the last twenty years to substitute gun-cotton for ordinary 
powder for firearms and mines have resulted in most opposite conclusions. In France, 
after numerous experiments, it has been discarded on account of its detrimental effect 
on the metal of firearms, and accidents from spontaneous combustion and explosion, first 
brought into notice by a memoir presented by us to the Institute in 1849. 
In Austria, General Lenk has continued to occupy himself with the manufacture and 
use of this explosive material. He prepares it by a process which has been followed on 
a large scale at Hirtenberg, and which remained for some years a profound secret. But 
during the last year papers on this subject have been published by German chemists and 
by General Lenk himself. 
It would appear from these papers that the Hirtenberg pyroxylin does not decompose 
spontaneously, like that made in France at the Bouchet powder-factory, and moreover 
differs from the latter in its composition, and in the circumstance that its explosive 
power may be regulated by particular arrangements. We will now examine the value 
of these assertions, giving the results of some experiments and analyses we have made 
with the co-operation of MM. Faucher and Chapoteaut. 
Processes followed at Hirtenberg and at Bouchet .—The pyroxylin made at Hirtenberg 
by General Lenk’s process is, like the Bouchet pyroxylin, the product of the immersion 
of cotton in a mixture of monohydrated nitric acid and sulphuric acid at 66 . The 
two methods, however, differ in several respects. 
Thus, the proportions of the two acids are not exactly the same, Lenk’s mixture being 
