TRANSACTIONS OF THE SECTIONS. 61 



ing a solution of ferrocyanide of potassium to one of chloride of anti- 

 mony ; at the request of the Professor, Mr. R. Phillips undertook to 

 examine the pigment in question, and has communicated the following 

 observations. 



" Having by me some chloride of antimony, which I employ on or- 

 dinary occasions, I added to it some ferrocyanide of potassium, and im- 

 mediately produced the blue precipitate. This solution had, however, 

 a very slight yellow tint, and remembering that Professor Clarke had 

 shown me that hydrochloric acid very much deepens the colour of 

 perchloride of iron, I suspected its presence ; I therefore prepared some 

 chloride of antimony from hydrochloric acid, and a protoxide which I 

 believed to be pure. I obtained a perfect colourless solution, and in 

 this no blue precipitate was formed by ferrocyanide of potassium. 



" To show that the chloride of antimony, which I first employed, 

 contained peroxide of iron, I decomposed a portion of it by the addi- 

 tion of water; the solution gave a much deeper blue precipitate than 

 before, while the oxychloride of antimony, re-dissolved in hydrochloric 

 acid, gave scarcely any blue tint whatever ; and the slight one which 

 it did yield was evidently owing to the adhesion of a small portion of 

 peroxide of iron precipitated with it ; for, again precipitating with water 

 and dissolving in hydrochloric acid, this minute portion of peroxide of 

 iron was almost entirely removed. 



" It is therefore evident, that the blue pigment is merely Prussian 

 blue, largely diluted and rendered pale by ferrocyanide of antimony." 



The author again adverts to the curious fact, already alluded to as 

 pointed out to him by Professor Clarke, of the colour imparted to hy- 

 drochloric acid by perchloride of iron. A few drops of the perchloride 

 were rendered perfectly colourless by half an ounce of water, while 

 three ounces of colourless hydrochloric acid acquired a considerable 

 yellow tint by the addition of a similar quantity of the perchloride. 



Oh tlie Blue Pigment of Dr. Traill. By C. T. Coathupe. 



Mr. Coathupe stated other experiments which confirm the conclusion 

 of Mr. R. Phillips, that the colour in question could not be produced 

 from pure chloride of antimony. 



A new case of the Chemical Action of Light in the Decoloration of 

 Recent Solutions of Caustic Potass of Commerce. By R. Mallet. 



The author of this paper has examined chemically a large number 

 of specimens of commercial caustic potass, with a view to determine 

 the reality of the cause usually assigned to the deep green colour 

 of its aqueous solutions, namely, the presence of manganese, in the 

 state of manganesiate of potdss. The colour of these solutions gra- 

 dually fades in close or open vessels, and in light or darkness, an effect 

 which has been ascribed, as above, to their containing mineral ca- 



