108 
POPULAR SCIENCE REVIEW. 
Spontaneous Conversion of Gun-cotton into Pectic and Parapectic Acids . — 
Under this title a very interesting paper, by Professor Divers, appears 
in the journal of the Chemical Society. The discovery was, in part, the 
result of accident. A quantity of pyroxylin which had been prepared 
from Swedish filtering paper, and which was quite free from adhering 
acid, was exposed for about two years to the influence of diffused light. 
When the bottle was opened at the expiration of this period a quantity of 
gas escaped with violence, and the fumes of nitrous acid were developed. 
Having been left by for a considerable time, with the orifice of the bottle 
partially closed, the contents deliquesced into a consistent jelly. The 
gelatinous material was then submitted to repeated washings, which were 
of an exceedingly acid character ; both jelly and washings were preserved, 
and from their conduct with various reagents the author has arrived at the 
conclusion that the former was pectic and the latter parapectic acid. 
The Origin of Nitrites. — In a comparatively recent communication to 
the Academy of Sciences of Munich, M. Schoenbein put forward a very 
valuable explanation of the mode in which these salts are formed. “ If * 
pure water be boiled in an open vessel — a porcelain capsule, for example, 
and a few grammes of the vapour thus formed be condensed by holding 
over the vessel a cold flask or a sheet of filtering-paper saturated with 
distilled water, a liquid may be obtained which, when acidulated with 
sulphuric acid, gives a feeble but appreciable stain to starch solution con- 
taining iodide of potassium.” This reaction, M. Schoenbein asserts, is due 
to the presence of a small quantity of nitrite of ammonia. The same 
results are arrived at more decidedly when paper steeped in a solution of 
potass has been employed. And this effect is also produced when the 
water is evaporated at a much lower temperature, as, for example, 40° or 
70° per cent. If water be evaporated at 40° or 50° during a period of twenty- 
four hours, and that the condensed vapour be continually poured back 
into the retort, it will be found that at the end of that time the liquid con- 
tains a large quantity of nitrites. The author showed that even at the 
ordinary temperature the same formation of nitrites occurred. These salts 
are converted, through the action of ozone into nitrates, and hence if 
potash be present ordinary saltpetre will be formed. It follows from this 
discovery that soils — particularly those of warm climates — are being 
constantly supplied with ammoniacal salts ; on this account M. Schoen- 
bein says there is much reason to believe that Baron Liebeg is correct 
when he states that it is useless to furnish plants with a large quantity of 
ammoniacal manure, inasmuch as it is only necessary to supply the 
purely mineral ingredients of soils. M. Schoenbein supposes that plants 
must also contain nitrites in large quantities. He finds that the freshly- 
pulled leaves of Leontodon taraxacum , bruised and mixed with water in the 
proportion of one part by weight of leaves and a hundred of water, form a 
liquid which, when acidulated with sulphuric acid, gives a deep blue with 
the iodide of potassium and starch. The leaves of the following plants 
possess similar properties : — Lactuca sativa , Senecio vulgaris, S. erucaefolius, 
Dactylis conglomerata, Plantago major, Mentha piperita, Thymus ser- 
pyllum. Spinacia oleracea, Datura stramonium, Hyoscyamus niger, 
Nicotiana tabacum, Helianthus annuus, and Papaver somniferum, exhibit 
