^14 TRANSACTIONS OF THE [APRIL 5, 



The cavities in wliieh these crystals occur are usually lined 

 with small minute crystals of quartz. Small particles of" obsid- 

 ian were also seen disseminated through the mass. 



From the same county have been sent some transparent 

 quartz crystals, two inches in length by one inch across, coated 

 with chlorite, and penetrated in every direction by crystals of 

 byssolite. 



Dr. H. Carrington Bolton spoke upon 



PEROXIDES 01- potassium AND SODIUM. 



A Lecture Experiment. 



The peroxide of potassium, K,0^, and the peroxide of sodium, 

 Xa^O,, were known to Gay Lussac and Thenard ' as early as 

 1810, by whom they were obtained in minute quantities in vari- 

 ous ways. They have been analyzed and closely studied by 

 Vernon Harcourt,' who prepared them by burning the re- 

 spective metals in dry oxygen gas, 



I have devised a simple method for exhibiting to a class the 

 formation And some of the characteristics of these peroxides. In 

 a test-tube suspended by a wire from an iron stand, a quantity 

 of potassium nitrate is melted over a Bunsen burner and heated 

 until oxygen gas is freely liberated; on dropping into the melted 

 nitrate small pellets of clean potassium, the metal burns with a 

 bright light, and forms the yellowish peroxide; this gradually 

 sinks beneatli the surface of the melted mass and dissolves 

 therein, communicating to the whole a deep, rich, red color; 

 the color is easily shown I)y the aid of transmitted light. On 

 allowing the melted mass to cool and solidify, the color disap- 

 pears, but reappears on again applying heat. 



If sodium nitrate and metallic sodium be used, similar phenom- 

 ena are observed, but the solution of the peroxide has a yellow- 

 ish-red color. The action of sodium on melted saltpetre pro- 

 duces a brown-red solution quite intense when sufficiently 

 heated. On cooling, in each case the mass loses its color. 



These reactions are quite consistent with the properties of the 

 peroxides as described by Harcourt; potassium peroxide, he 

 says, is '^ deep orange-yellow and fuses to a black fluid "; sodium 

 peroxide is white when cold, becomes "full yellow" on heating, 

 and when fused is " black while hot, brown on cooling." More- 

 over, we prepared a small quantity of sodium peroxide in the 

 ^sual way, by burning the metal in dry oxygen, and ascertained 



' Recherches physico-chimiques, i., 133. 

 •-' Quart. J. Chera. Soc, xvi., 267 (1861). 



