Chemical Society. 341 



and given away among his friends ; Dinneford was also employed to 

 make it, and also an agent for the sale of it in Manchester.' " 



The following is Mr. Mercer's mode of preparing this oxide : 

 — " Take a quantity, say one pound of the common crystallized pro- 

 tosulphate of iron, dissolve it in water, and add nitric acid in sufficient 

 quantity to peroxidize it, and afterwards expel carefully all excess of 

 nitric or nitrous acid by boihng. To this add one pound of protosul- 

 phate of iron, with water sufficient for its solution. Pour the mixture 

 into a solution of caustic potash sufficient in quantity and strength to 

 decompose the whole, and then boil. The precipitate thus thrown 

 down consists of a mechanical mixture of the protoxide and peroxide 

 of iron atom to atom; raise the temperature of the mixture to 212° 

 Fahrenheit, and their chemical union is effected. That such is the 

 succession of changes is proved, by dipping into the mixture, pre- 

 vious to boiling it, a piece of clean cotton cloth, which, after ex- 

 posure to the air for a few minutes and washing in water, exhibits 

 the buff stain peculiar to peroxide of iron precipitated upon cotton 

 fibre. But if this is performed after the boiling a dirty black stain 

 is obtained, indicating the formation of the black oxide," 



This fact is further proved by the oxide, after boiling, having 

 a crystaUine structure, when examined under the microscope, the 

 minute plates having a brown colour and being transparent, although 

 the edges of the crystals are not sufficiently defined to trace the form. 



Mr. Thomson adverts to the apphcation of the artificial magnetic 

 oxide of iron, either in a dry or moist state suspended in water, as 

 a substance well adapted, from its extreme susceptibility of mag- 

 netic influence, to indicate the direction of magnetic or galvanic 

 currents, the magnetic curve described by Dr. Brewster being beau- 

 tifully exemphfied by the use of this oxide. 



" On the Influence of Water in Chemical Reactions," by Mr. 

 E. A. Parnell. 



Nov. 16. — The following communications were read : — 



"On the Analysis of the Oils of Laurel Turpentine, Hyssop, and 

 Assafoetida," by Dr. John Stenhouse. (See Memoirs, Vol. I., Art. 7.) 



An extract from a letter from Dr. Clark, " On the Revision 

 and more exact Determination of Atomic Weights." 



Dr. Clark finds, that when the proper correction, for weighing in 

 a vacuum instead of in air, is applied to the weighings made by 

 Berzehus, in his experiments on the formation of water, by passing 

 hydrogen gas over ignited oxide of copper, the results are very sen- 

 sibly altered. " Berzelius gives 



" Copper (metal) 39.''r0 Water produced 11 2-433 1 Mean 112-491 



Peroxide of copper 495-0 ... 112-C19 I ^- -128 



Increase, oxygen ToO ii„. „„ I" i i^o^.n^^"' ~ '^^^ 



' '° llciice liydrogcn 12-49 



" But if weighed In a vacuum the increase of 100 for oxygen and 

 the weight of 1 12-491 for water would both have lieen greater. The 

 following would be the corrected numbers: — oxygen, 100-02G6; 

 water, 1 12-013 ; or oxygen being 100, water will be 1 12-583. Hence 

 hydrogen 12-.';83, in air 12-491, correction + 0092. As to Berze- 

 lius and Dulong's experiment.? on the specific gravity of gases, how- 



