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POPULAR SCIENCE REVIEW. 
stances under certain circumstances. If a few drops of a solution of a salt 
of arsenic, or arsenious acid, is put into a few ounces of dilute sulphuric 
acid, and the mixed solution agitated at intervals with recently ignited char- 
coal, for an hour or two, the clear liquid obtained by filtration does not 
manifest any reaction of arsenic when tested by Marsh’s process. Lignite 
has not the same efiect as charcoal, though absorbent of weak acids and 
bases generally, as Mr. Skey has before shown. Timgstic acid also from 
acid solutions is removed by charcoal applied in like manner, and is given 
up to a solution of caustic alkali. 
An Aniline Marking-ink, said to be indelible, is now commonly prepared 
in France by mixing the two following solutions : — a, cupreous solution — 
8'52 grm. of crystallised chloride of copper, 10’65 grm. chlorate of soda, 
and 5 ’35 grm. of chloride of ammonium, are dissolved in 60 grm. of dis- 
tilled water ; h, aniline solution — 20 grm. of hydrochlorate of aniline are 
dissolved in 30 grm. of distilled water, and 20 grm. of a solution of gum 
arabic (1 of gum to 2 of water) with 10 grm. of glycerine are added. By 
mixing in the cold four parts of the aniline solution with one part of 
the cupreous solution, a green liquid is obtained, which can be used im- 
mediately for tracing characters upon linen; the marks, however, alter 
after the lapse of a few days. It is necessary to keep the solutions separate 
until required for use. If the fluid does not flow easily from the pen, it 
may be diluted without fear of diminishing the intensity of the tint, which, 
at first green, gradually darkens and becomes black. Heat causes the change 
to take place instantaneously ; a steam heat is sufficient, and is better for 
the fabric than a hot iron. Afterwards the linen is washed in warm soap 
and water. This ink resists acids and alkalies, and is remarkably permanent. 
Organic appearances in Colloid Silica . — At the meeting of the Chemical 
Society on April 2, Mr. W. Chandler Eoberts read an extremely interesting 
paper on this curious subject. The colloid silica was, of course, obtained by 
dialysis. The results arrived at were very remarkable, and were elucidated 
by a series of specimens, both of artificial and natural origin, the structures 
of which were demonstrated by the aid of a microscope and illustrative 
drawings. In experimenting upon somewhat large quantities of soluble 
silicic acid prepared in Graham’s dialyser, a portion of the liquid product 
was evaporated slowly in air to compare with the forms of hydrous silica 
left by a more rapid operation conducted in vacuo. All the specimens of 
jelly dried in air exhibited dendritic forms, varying in size from 0-2 to 0*5 
m.m. ; these were at first supposed to afford indications of the passage of 
colloid into crystalloid silica, but when magnified 90 linear they appeared 
as radiating fibres, and upon being further magnified 700 times each fibre 
resolved itself into a collection of elongated beaded cells, with clusters of 
circular cells at intervals. Such a structure would indicate a vegetable 
growth, and the author concludes that the markings, which are similar to 
those seen in moss agates and Mocha stones, are due to the growth of fungi 
or mildew in the partially solidified jelly. The spores of organic life were 
probably derived from the air, since no evidence of similar structm’e was 
visible in the specimens of hydrous silica obtained in the desiccator. These 
last-named products were very like the opal from Zimapan, but contained 
21 ’4 per cent, of water. 
