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POPULAR SCIENCE REVIEW. 
deposit afterwards. The three colours are not destroyed, for each can he 
separated by analysis with the characteristic properties. 
Action of Sulphurous Acid on silver Compounds. — In a communication to the 
Chemical News (Aug. 21) Professor J. S. Stas gives an account of his recent 
observations on this subject : — A current of sulphurous anhydride, prepared 
by means of the combustion of sulphur in dry air, or by the decomposition 
of sulphuric acid by copper, mercury, carbon, or wood, produces a white 
precipitate of sulphite of silver in an aqueous solution of nitrate or sulphate 
of silver; the liquid remains colourless. A solution of sulphurous acid, 
newly obtained by passing the anhydride through boiled water, and ^’ro- 
tected from the action of the light, behaves like the anhydride. The sulphite 
of silver produced, kept from the light, seems to him to keep indefinitely at 
common temperatures ; but under the influence of light, or of an excess of 
sulphurous acid, it changes into a mixture of sulphate of silver and metallic 
silver. A current of sulphurous anhydride, or a fresh saturated aqueous 
solution of this anhydride, does not precipitate sulphite of silver from a 
solution of nitrate or sulphate of silver, dissolved in water acidulated by a 
sufficient quantity of sulphuric or nitric acid ; the liquid remains colourless. 
In complete darkness, the liquid may even be kept for a long time at 100° C., 
without the slightest precipitate or change of colour. A solution of sul- 
phurous acid in pure water, whether boiled or not, after being left for some 
time in the light, gives a grey precipitate with sulphate and nitrate of 
silver; in a few moments the supernatant liquid becomes successively 
yellow, brown, and black, and at length throws down sulphide of silver. 
He has seen such a solution of altered sulphurous acid precipitate, in dark- 
ness, metallic silver from a solution of nitrate or sulphate of silver in dilute 
sulphuric acid, and even in dilute nitric acid. 
A new ammoniated Chloride of Zinc. — In the course of some recent re- 
searches on a new class of zinc compounds Dr. Edward Divers succeeded in 
discovering a pentammoniated chloride of zinc. This discovery is of no 
inconsiderable importance since it adds another to the three zinc chlorides 
already described by Sir Robert Kane. The following is the process by 
which the new compound is obtained : — Solid zinc chloride is dissolved in 
the strong solution of ammonia of commerce, and as the solution of the first 
portions of chloride is attended with a marked rise of temperature, it is 
advisable to add the salt gradually, to close the vessel tightly to prevent 
expulsion of the ammonia, and to cool the vessel by a stream of cold water. 
When the solution of the zinc chloride becomes exceedingly slow, ammonia 
gas is passed into the liquid. If this is kept cool a crystalline precipitate 
soon forms ; if, on the contrary, the liquid is not kept cool by the application 
of external cold, the liquid usually remains clear for some time. When the 
liquid in the cold state contains a moderate amount of deposit, the passage 
of ammonia into it must be stopped ; then on closing the vessel containing 
it, and heating gently and shaking, the crystalline deposit may be redis- 
solved. On cooling, the solution gradually yields the new chloride in large 
crystals of remarkable appearance. They are regular octohedra, with 
perfect angles and edges, but with deficient faces ; that is to say, the faces 
are hollowed out in a series of steps from the edges to the centre of the 
face, so as to exhibit a structure similar to that seen in the hollow pyramidal 
