SCIENTIFIC SUMMAKT. 
429 
crystallisations of sodic cUoride. The mode in which such crystallisations 
of sodic chloride are produced is well known to he the formation of a small 
cube of the salt at the surface of the brine, to which it adheres by one of 
its faces, causing a depression in the fluid surface because of its density, and 
then the gradual addition to the upper external edges of the crystallisation 
of successive square courses of the sodic chloride. The formation of the 
hollow faces of the octohedra of the new ammoniated chloride of zinc is 
apparently partly similar to this — comparatively large crystals sometimes 
hanging from the surface of the mother liquor by a hollow face. But then 
all the faces of these octohedra are thus hollowed out so that their forma- 
tion can have no necessary connection with crystallisation at the surface of 
the fluid and to make the crystals of sodic chloride similar in their 
hollowed form to these octohedra, the cubical piece at the apex of the 
pyramid would have to be the centre and common apex of six such pyra- 
mids united in the form of a cubical flock with hollowed faces. 
The Coloration of Peroxide of Nitrogen.- — A very interesting note on this 
subject by M. Salet appears in the Comptes Pendus, Aug. 24. The author 
endeavours to explain the curious relation which exists between the dimi- 
nution of density and increase of coloration. 
Volumetric estimation of Zinc. — In a paper presented to the French 
Academy (Aug. 17) M. A. Renard gives an account of his process for the 
above purpose. If, he says, to a determined solution of yellow prussiate 
of potash you add a solution of a salt of zinc, the zinc is wholly precipi- 
tated in the form of a double ferrocyanide of zinc and iron, completely 
insoluble in ammonia. By determining with potassic permanganate the 
excess of prussiate of potash employed you obtain by easy calculation the 
quantity of zinc. 
Chlorosulphuric Ether. — M. Th. de Purgold describes this substance, which 
is procured by directing the vapour of chlorhydric ether through anhy- 
drous sulphuric acid. This peculiar compound has the following formula : 
CaH^ClSO^. 
Persulphide of Hydrogen. — The last number of the Proceedings of the 
B.oyal Society (No. 103) contains a paper by Dr. Hofmann, on the constitu- 
tion of this remarkable body. The views of chemists being known to differ 
remarkably in reference to the chemical composition of this substance. Dr. 
Hofmann was led to examine carefully a compound which he accidentally 
discovered, and which appears to throw some light on this subject. On 
adding a cold saturated solution of strychnine in strong alcohol to an 
alcoholic solution of polysulphide of ammonium, brilliant crystalline 
spangles soon appear, and after twelve hours the walls of the vessel are 
covered with beautiful orange-red needles often a centimetre long, and 
which have only to be washed in eold alcohol to render them perfectly pure. 
Analysis of them has led to the formula : — C 31 H 22 N 2 O 3 , H 2 S 3 . Hence Dr. 
Hofmann concludes that the crystals are a compound of one molecule of 
strychnine and one of persulphide of hydrogen of the composition H 2 S 3 . 
That this is really the constitution of the compound is proved by the fact 
that in contact with concentrated sulphuric acid the crystals are decolorised 
and an addition of a small quantity of water, colourless transparent oily 
drops of persulphide of hydrogen are separated, sulphate of strychnine 
