1870.J Physics. 427 



charcoal at Laud, the jeweller took coal for heating the muffle for 

 euauielliug, an operation which succeeded most perfectly ; but on 

 taking the buttons from the muffle, the jewels had become perfectly 

 black, and no amount of rubbing or friction restored them to their 

 pristine state. The jeweller was therefore obliged to dismount the 

 jewels, which looked like plumbago, and to send them to Paris, 

 when by the first touch of the lapidary's wheel they became restored 

 to their former beauty ; while, curiously enough, their weight had 

 not changed. Professor Morren who, through the kindness of MM. 

 Laurin, jewellers at Marseilles, was enabled to experiment with 

 several diamonds, placed them on a small platinum boat in a pla- 

 tinum tube, and tried the effect of a high temperature simultaneously 

 with different gases. Heated in coal-gas the gems become blackish, 

 increase in weight, and are found to be coated with a strongly- 

 adhesive layer of carbon, such as is deposited in gas retorts ; in 

 pure hydrogen, the gems may be heated almost to the melting- 

 point of platinum without undergoing any change ; heated in car- 

 bonic acid gas, the gems become dull and lose a little weight. The 

 carbonic acid gas was found to be dissociated into carbonic oxide and 

 carbonic acid ; this, the author found, was caused by the platinum 

 and not by the diamond. When the diamond is placed in oxygen 

 gas and ignited, it continues to burn, but remains white, appearing 

 as a piece of unpolished glass ; the stone does not blacken, nor swell 

 up, and, if it is free from flaws or cracks, does not split asunder. 



Dr. Janssen, who, it will be remembered, went to India for the 

 purpose of observing the total solar eclipse, has communicated some 

 observations on the artificial production of ice in India. In many 

 parts of the Indian continent, the natives dig shallow pits in localities 

 which are freely open to the sky and distant from trees. The pits 

 are lined with straw, and upon the straw are placed dishes (made 

 of a very porous earthenware) filled with water. During the calm 

 and clear nights prevailing in the period from November to the end 

 of February the water placed in the dishes freezes, yielding a solid 

 cake of ice, while the temperature of the air is -j- 10°. Dr. Janssen 

 has investigated this curious subject experimentally, and has found 

 that the freezing is principally due to the radiation during the night ; 

 but the evaporation of the water, aided by the porosity of the 

 earthenware employed, is at the same time not to be overlooked. 



In order to exhibit the effect of the expansion of water when 

 freezing, F. Kiidorff fills with distilled and previously well-boiled 

 and cooled water a cast-iron cylinder, having the following dimen- 

 sions: — Height, 160 millimetres ; diameter (external), 50 millimetres; 

 thickness of solid iron, 15 millimetres. After having been filled 

 with water this apparatus is closed by means of a plug screwed into 

 the neck, and the cylinder is next placed in a mixture of three parts 



VOL. VII. 2 G 



