320 
POPULAR SCIENCE REVIEW. 
be detected in tbe ash. left upon burning tbe washed and dried cotton. 
Similar experiments made upon wheat, French beans, and walnuts gave 
like results, much phosphoric acid and magnesia being discovered in the 
aqueous solution. 
Sow to know 'pure Glycerine. — A writer in an American Pharmaceutical 
periodical makes the following remarks relative to the best mode of testing 
the purity of a sample of glycerine : — “ I should regard a glycerine as unob- 
jectionable for medicinal purposes, if it forms a colourless mixture with twice 
its volume of strong alcohol and of sulphuric acid ; and if, after previous 
dilution with distilled water, it yields no turbidity, either cold or on heating 
to the boiling point with sulphuretted hydrogen, ferrocyanide of potassium, 
nitrate of baryta, oxalate of ammonia, or nitrate of silver. This last test I 
regard as an important one, since 1 believe that all those compounds, which 
impart to common glycerine a peculiar rancid odour, will reduce the silver 
salt and impart a colour to the liquid on boiling, even though that odour may 
be scarcely apparent, while pure glycerine is not affected by boiling with 
nitrate of silver, although, like nearly all organic and many inorganic 
compounds, it gradually assumes a darker colour on exposure to light. 
Chloride of Silver in the Estimation of Iodine. — M. Kraut has devised a 
useful mode of determining the iodine contained in organic hydriodates, of 
which the Chemical News gives a short account. Herr Kraut digests the 
solution for several minutes with a known quantity of recently precipitated 
chloride of silver ; the increase of the weight of the chloride of silver is in 
proportion to the amount of iodine. This method has the advantage of not 
altering the substance beyond the removal of its iodine, which is replaced by 
chlorine. — Zeitschrift fur analytische Chemie , iv. 167. 
A Chemical Method for effectually cleaning Glass is given in a recently 
published work on one of the processes of photography. It is simple, reliable 
and completely efficient, and will we doubt not be found very useful by our 
readers. It is as follows: — Dilute the ordinary hydrofluoric acid sold in 
gutta-percha bottles, with four or five parts of water, drop it on a cotton 
rubber (not on the glass), and rub well over, afterwards washing till the 
acid is removed. The action is the same as that of sulphuric acid when used 
for cleaning copper $ a little of the glass is dissolved off, and a fresh surface 
exposed. The solution of the acid in water does not leave a dead surface on 
the glass, as the vapour would ; if a strong solution is left on long enough 
to produce a visible depression, the part affected will be quite bright. This 
method is recommended in some cases for cleaning photographic plates. 
Vide the u Tannin Process,” by Major Russell : R. Hardwicke, 192 Piccadilly. 
Capillary Action and Chemical Decomposition. — The relation of the two 
phenomena has been well demonstrated in a recent experiment by M. 
Becquerel, who shows that both decomposition and combination are 
influenced by capillary attraction. He takes a tube with two branches re- 
versed, and makes in it a fissure, the width of which is infinitely small. He 
pours therein a solution of nitrate of copper, and has found that no liquid 
passes by the fissure ; but when placed in a vessel containing liquid pro- 
tosulphuret of sodium, an electrical action takes place, and decomposition 
and recomposition ensue, manifested by the crystals which appear on both 
sides of the fissure. M. Becquerel has demonstrated the new and curious 
