TRANSACTIOXS OF THE SECTIONS. 76 



contact with each other. Most other organic iodides may be substituted for the 

 allylic iodide, those of amyle or etliyle for instance. Tlie reaction is, however, 

 slower in these cases, and sometimes requires an elevation of temperature. The 

 crystals mentioned contain no organic substance ; they are freely soluble in ether, 

 and show exactly the composition of one atom of bromine and one atom of iodide 

 for one atom of mercury. They form rhombic prisms exactly isomoi'phous with 

 the yellow unstable modification of biniodide of mercury. Dr. Grothe found the angle 

 otp : ju=114° 25', while for the yellow iodide Mitscherlich determined ^ : />=114°, 

 the corresponding angle in the bibromide being = lll° 2G'. The angular differences 

 of the three isomorphous compounds do not therefore correspond exactly with their 

 chemical differences. 



It is quite evident that this iodo-bromide is not an isomorphous mixtiire, but a 

 chemical individual, although the author has not been able as yet to give the most 

 decisive proof of it by taking the vapour-density of the compound, its boiling-point 

 being considerably higher than that of mercury ; this being also the case with the 

 biiodide and bibromide of mercury. The bromo-iodide is, however, a very stable 

 compound. It may be sublimed without breaking up into the bromide and iodide ; 

 and what appears decisive, its melting-point lies just in the middle between the 

 fusing-points of the bromide and of the iodide, viz. at 229'C. 



The fusing-point of Hg Br, is situated between 222° and 223°C., and that of Hg I^ 

 at 238°. The latter compound is transformed into its yellow modification between 

 148° and 154°, the bromo-iodide shows no such changes. Lastly, it should be 

 remarked that when the quantity of bibromide of mercury acted upou by the or- 

 ganic iodide is insufficient to produce the reaction described, 



C3 H, I+Hg Br, = C3 H, Br-hHg I Br, 



then crystals of red iodide of mercurj' are formed at the same time, but never any in- 

 termediate bromo-iodides, save the one described. Its existence may therefore be 

 fairly taken as an additional proof for the atomic weight of mercmy, such as it is 

 now generally accepted. 



The author has been particularly careful to ascertain the complete absence of bro- 

 mine in the crystals of iodide of mercury formed along with it, because they show a 

 peculiarity not hitherto observed. The red crystals, although belonging to the tetra- 

 gonal system, show the phenomenon of double refraction, but this evidently only in 

 consequence of a certain pressure they were subjected to in the mother-liquor from 

 which they crj'stallized. The reaction described is by no means the only one 

 which engenders the bromo-iodide of mercury. When coiTesponding quantities of 

 Hg Br, and Hg I, are dissolved in acetone, the same compound will crystallize 

 out ; as also when iodine is added to an acetonic solution of the bibromide. 



On the SoliibiliUf of Lead and Copper in pure and impure Water. 

 By Dr. T. L. Phipson, F.C.S. cJt. 



In this paper the author compares the action of certain natural waters upon 

 various metals. The waters were — Surrey spring water, yielding 17 to 24 gTains of 

 solid matter per gallon ; spring water fi-om Crawford, yielding only 10| grains per 

 gallon ; pure distilled water, and Thames water as supplied to the inhabitants of 

 Putney, yielding 40 to 49 grains per gallon. The metals were submitted to pro- 

 longed friction, and to contact of air whilst these waters acted upon them. They 

 were iron, lead, union metal, copper, tin, and zinc, of various qualities, both pure 

 and commercial varieties. The most important conclusion anived at in these ex- 

 periments was, that in the above conditions all these different waters attacked and 

 dissolved lead, union metal (an alloy of lead, antimony, and tin), copper, and per- 

 haps zinc. The method of experiment consisted in placing some 5 to 10 gi-ammes 

 of the metal, cut into small pieces, into a pint stoppered bottle, three-fourths full 

 of the water to be tested. The whole was submitted to violent shaking for about 

 36 hours ; the liquid was then filtered through the finest Swedish filtering paper, 

 and received in a white porcelain capsule 6 inches wide. A drop of sulphide of 

 ammonium added to the filtrate showed that metal had been dissolved by imme- 

 diately giving a brown tinge to the whole liquid. The experiment was slightly 



