Chemical Science. 235 



dry chloride. The hydrate itiay be decomposed, and a pure 

 chloride obtained, by distilling: the mixture from a sufficient quan- 

 tity of conceutrated sulphuric acid. — Dumas, Ami. de Chimie, 

 xxxiii. 360. 



14. Preparation of Oxide of Chrome, as a Pigment^M. Nasse 

 recommends that a chromate of mercury should be formed, ac- 

 cording^ to the usual process, by precipitation from a chromate of 

 potash and a nitrate of mercury, as neutral and concentrated as 

 possible. The oxide of chrome, obtained by heating" the chromate 

 of mercury, will have the greatest perfection of colour, if it be 

 put into an unglazed porcelain crucible, and exposed to the heat 

 of the furnace during the time required for baking the porcelain. 

 The oxide produced will have a fine grass-^een colour. 



The following directions are given for the preparation of the 

 blue oxide : the concentrated alkaline solution of chrome is to be 

 saturated with weak sulphuric acid , and then to every 8lbs. is to be 

 added lib. of common salt and half a pound of concentrated sul- 

 phuric acid ; the liquid will then acquire a green colour. To be 

 certain that the yellow colour is totally destroyed, a small quan- 

 tity of the liquor is to have potash added to it, and filtered ; if 

 the fluid is still yellow, a fresh portion of salt and of sulphuric 

 acid is to be added : the fluid is then to be evaporated to dry- 

 ness, re-dissolved and filtered ; the oxide of chrome is then to be 

 precipitated by caustic potash. It will be of a greenish-blue 

 colour, and being washed, must be collected upon a filter. — 

 BuU. Univ. E., vi.275. 



15. Separation of Iron from Manganese, — The novelty of situ- 

 ation in which the chemical analyst is frequently ])laced, in pur- 

 suing his intricate experimental inquiries, often renders one process 

 for the separation of substances useful, when another of a gene- 

 rally superior character is inadmissible. It is for this reason that 

 we insert at present a mode of separating iron from manganese, 

 proposed by M. Quesnevile, jun. : — Dissolve both oxides in muri- 

 atic acid, and boil the solution for some time, to expel all excess 

 of acid, in order to render the solution as neutral as possible. 

 Dilute the solution with a large quantity of water, and pass 

 chlorine gas through it, to peroxidize the iron entirely ; then pre- 

 cipitate the liquor by arseniate of potash : the precipitate is of 

 a greenish-white colour, and consists entirely of arseniate of iron. 

 After some hours, filter the liquor, and wash the precipitate with 

 a large quantity of boiling water ; dry it, and calcine it strongly, 

 to obtain the oxide of iron ; evaporate the solution, which con - 

 taius the arseniate of manganese, almost to dryness, and add water to 

 it ; if there remain by accident any traces of arseniate of iron, it 

 separates : then filter and decompose the solution by caustic 

 potash, and the oxide of manganese, when well washed, is then 

 i^erfectly pure. — Jour, de P/iar., Sept., 182(5. 



