303 Royal Society .— 



hydrochloric acid by baryta-water, and by drying in vacuo the pre- 

 cipitate thus obtained. The peroxide of barium thus procured is 

 perfectly pure, with the exception of a trace of carbonate. In ap- 

 pearance it resembles magnesia. 



To prepare the peroxide of benzoyle, the chloride of benzoyle and 

 the peroxide of barium are taken in equivalent proportions and mixed 

 in water. A mutual decomposition takes place ; and a substance is 

 formed which, after crystallization from anhydrous ether, gave the 

 following results to analysis : — 



Carbon 69-23 



Hydrogen 4*10 



Oxygen 26-67 



100-00 



The calculated numbers for the peroxide of benzoyle are 



C„ 168 69-42 



Hjo 10 4-13 



O, _64 26-45 



242 100-00 



This substance contains an atom of oxygen more than the anhy- 

 drous acid, and (reducing the formula to its simplest expression) one 

 atom of hydrogen less than the hydrated acid. Thus we have 

 C,^ H,„ O3 anhydrous benzoic acid, Cj , H,„ O, peroxide of benzoyle, 

 and C^ H„ O^ hydrated benzoic acid, C^ H^ O., peroxide of benzoyle, 

 as we have H„0 water, and H2 O, or HO for the peroxide of hydro- 

 gen. This body crystallizes from ether in large and brilliant cry- 

 stals. Heated a little above the boiling-point of water, it decom- 

 poses, with a slight explosion and the evolution of carbonic acid. 

 Boiled with a solution of potash, it is resolved into oxygen gas and 

 benzoic acid. 



The peroxide of acetyle is prepared by mixing anhydrous acetic 

 acid and peroxide of barium, in equivalent proportions, in anhydrous 

 ether. The mixture is to be effected very gradually, being attended 

 with evolution of heat. The ether, after filtration from the acetate 

 of baryta produced, is to be carefully distilled off at a low tempera- 

 ture, and the fluid which remains washed with water. After three 

 or four washings, the water ceases to be acid, and a viscid liquid re- 

 mains, which is the peroxide of acetyle. This substance possesses 

 the following properties: — It is extremely pungent to the taste ; the 

 smallest portion of it placed upon the tongue burns like cayenne 

 pepper. The substance suspended in water immediately decolorizes 

 a solution of sulphate of indigo. It instantly peroxidizes the prot- 

 oxide of manganese, and converts the yellow prussiate of potash into 

 the condition of red prussiate. Baryta-water poured upon the sub- 

 stance is converted to the condition of peroxide of barium, with for- 

 mation of acetate of baiyta. Lastly, a single drop of the substance 

 itself, placed on a watch-glass and heated, explodes with a loud re- 

 poit, shivering the glass to atoms. 



To analyse the peroxide of acetyle, I availed myself of its decom- 



