SCIENTIFIC SUMMARY. 
197 
Solid Carbon in Luminous Flames. — Dr. Heumann lias continued his re- 
searches upon luminous flames, and in a recent memoir considers the 
question of the cause of luminosity in the flames of hydrocarbons, and comes 
to the conclusion that it is the presence of solid incandescent particles of 
carbon. He founds this opinion on the following proofs : the increased 
luminosity produced by chlorine, which, as is well known, has the property 
of separating carbon ; the fact that a rod held in a flame gets coated with 
soot only on the lower side, whereas if the carbon were present as vapour 
it ought to be condensed by cooling, and therefore all round the body ; the 
fact that a body when held in the flame is coated with soot, even though kept 
in a state of ignition ; the fact that the particles of carbon can actually be 
seen in a flame when it is made to strike against a second flame or an ignited 
surface — the particles then become aggregated together to form larger 
masses, which become visible in the luminous mantle of the flame as so- 
many brilliant points : the fact that the transparency of the luminous portion 
of a flame is not greater than that of a layer of smoke of the same thickness 
arising from the flame of burning oil of turpentine, which is known to be 
filled with particles of carbon ; and that flames which unquestionably owe 
their origin to the presence in them of solid particles, give a shadow with 
sunlight precisely as do those of hydrocarbons, while luminous flames com- 
posed of gases and vapours only throw no such shadow (“Liebig’s Annalen,” 
December, 1876). 
Alterations in Glass. — M. V. de Luynes finds that glass, when exposed to 
atmospheric action, may undergo very considerable alterations. Some glass 
from a skylight in the Conservatoire des Arts et Metiers, which appeared 
unaltered when looked at perpendicularly to its surface, showed, under 
certain angles, numerous strise of remarkable regularit} r . When slightly 
heated, both surfaces of this glass exfoliated in the form of scales, the total 
weight of which was about — of the whole weight of the glass. Analysis 
showed that the scales contained 77*8 per cent, of silica, whilst the un- 
altered glass had only 65 per cent. When a fragment of the glass was 
placed in hot water, the latter penetrated by fissures from the circumference 
to the centre of each scale. In other specimens the additional proportion 
of silica in the scales was approximately the same, namely, 776 and 78‘4 
per cent, against 65-8 and 68 per cent, in the unaltered glass. Prom the 
examination of his specimens, M. de Luynes has ascertained that the glass 
in them is hard to cut, that they act generally upon polarized light like 
tempered glass, and that some of the scales show distinctly coloured fringes. 
He thinks that the preservation of transparency even in glass so profoundly 
altered may lead to an explanation of the efiect produced by the use of acid 
as a preventive of the irisation of window glass (“ Comptes rendus,’ 7 
February 12, 1877). 
GEOLOGY AND PALAEONTOLOGY. 
Microscopical Examination of Sands and Clays. — At present the investi- ' 
gation of the minute structure of various rocks, especially those of the so- 
called igneous and metamorphic series, is greatly attracting the attention 
