92 
POPULAR SCIENCE REVIEW. 
the makers use paper containing suhcarbonate of lime, sesquioxide of 
iron, &c. Now suhcarbonate of lime also colours litmus blue, and this 
compound gives up its base to acids with much greater difficulty than the 
blue potash-compound does. Therefore, in order to prepare the most 
delicate blue litmus-paper, the latter should be first soaked in hydrochloric 
acid, and then well washed, before applying the litmus. Ordinary red 
litmus-paper is much more sensitive to alkaline reaction than blue paper 
is to acid. M. Chevreul said that the most delicate means to detect 
acidity was to put a freshly-cut piece of campeachy-wood into distilled water. 
If free from alkali, the. colour will be yellow, but if there is a trace of 
alkali present, the tint is purple ; then add a minute quantity of acetic acid 
on the point of a quill, when the colour will turn yellow. This liquid 
becomes purple with a trace of alkali, and acids change the purple to 
yellow. 
Analysis of the Waters of Pergeze. By M. A. Bechamp. — We learn from 
our contemporary, the Chemical News , that M. Bechamp has discovered in 
these waters considerable quantities of acetic and butyric acids. This is 
the first time that organic acids have been found in a French spring. Upon 
examining the deposit of this water under the microscope, a considerable 
number of mobile corpuscles were observed, similar to those seen in native 
chalk. M. Bechamp supposes that these are the causes of the formation of 
the volatile fatty acids. 
The Compounds of Niobium. — M. Marignac, in a recent memoir, endeavours 
to disprove the existence of ilmenium. He believes that the niobic acid 
extracted from columbite is not a mixture ; that its density is about 4 - 5 ; 
and that the two products, obtained by M. Hermann, having densities of 5 
and 8 - 8, are mixtures of this acid with bodies of a greater and less density, 
chiefly tantalic and titanic acids. 
Detection of Free Sulphuric Acid in Acetic Acid. — The following simple 
process for this purpose is given in Boettger’s Polytechnisches Notizblatt : 
Boil about fifty cubic centimetres of the acid to be tested in a retort with a 
very small quantity of starch, until half the liquid is distilled ; after it has 
cooled, add a drop of tincture of iodine. If, under these circumstances, a 
blue coloration be produced, no sulphuric acid is present. If the blue colour 
does not appear, it may be concluded that sulphuric acid is present, which, 
by reacting on the starch, will have transformed it to glucose. With tinc- 
ture of iodine, glucose gives no particular coloration. Sulphuric acid, thus 
detected, may be estimated by the ordinary processes. 
A Neio Form of Gunpowder. — This peculiar compound, the invention of 
Herr G. A. Neumeyer, is said to possess the following properties : — 
1. The powder bums, but does not explode, if the air has access. 
2. Neither pressure nor percussion will cause it to ignite. 
3. Its explosive force is equal to that of ordinary powder or even greater. 
4. - It leaves behind less residue than ordinary powder. 
5. It does not attract more moisture from the atmosphere than ordinary 
powder. 
6. It leaves behind less powder-smoke than ordinary powder. Its smoke, 
moreover, is light, disappears quickly, and has no injurious effect on the 
health of the workmen. 
