PHYSICS. 231 



nitrous oxide at its upper part. Upon increasing the pres- 

 sure to 209 atmospheres, streams of liquid were seen flowing 

 down the lower portions of the tube. When they met the 

 mercury, they seemed to turn back. At 310 atmospheres, 

 the mercury, being in contact with the cooled part of the 

 tube, was frozen, and on quickly removing the refrigerating 

 apparatus it was seen covered with frozen air. 



Pictet has determined approximately the density of liquid 

 oxygen, and finds it to be the same as that of water, thus 

 confirming an d priori conclusion of Dumas. Knowing the 

 volume of the generator, of the conden sing-tube, and of the 

 potassium chlorate used, the temperature of the generator 

 when the decomposition was complete, the pressure before 

 and after condensation, and the variations of the manometer 

 after two or three consecutive jets, up to the point where the 

 limit between the liquid and gaseous states is attained, and 

 combining these data with the density of the gas, its pres- 

 sure and temperature, Pictet finds that at 146, the tem- 

 perature of the carbon dioxide bath, the pressure required 

 to liquefy the oxygen is 74.26 atmospheres. The weight of 

 liquid oxygen contained in the tube was consequently 45.467 

 grams, and it occupied a volume of 46.25 cubic centimeters; 

 hence the density is not far from unity. 



Thorpe, in a note to Nature, calls attention to a long-neg- 

 lected paper of Mr. Perkins, which was published in the Phil- 

 osophical Transactions for 1826, having been read on June 15, 

 in which Mr. Perkins announces that he had liquefied atmos- 

 pheric air, having obtained pressures of upward of 1000 at- 

 mospheres in an apparatus quite similar to that of M. Caille- 

 tet. The paper describes the appearances as the pressures 

 were gradually increased, and says: "At 1200 atmospheres 

 the quicksilver remained three quarters up the tube, and a 

 beautiful transparent liquid was seen on the surface of the 

 quicksilver, in quantity about , 2 J u part of the column of air." 

 Subsequently carburetted hydrogen was liquefied in the same 

 way. This was in the year 1822. 



Garnett has called the attention of physicists, in an article 

 in Mature, to the peculiar form of the rosettes obtained when 

 a drop of water is placed on a red-hot surface, as in Leiden- 

 frost's experiment. The outline of the drop did not form a 

 continuous curve, but was beaded in character, while within 



