272 ANNUAL OF SCIENTIFIC DISCOVERY. 



with considerable lustre, and as granules that are so dark-colored as to ap- 

 pear almost black. When heated to 212 deg. F., with water, the crystals are 

 not altered in their characters, but when gradually heated to 302 dcg. F., 

 they become almost black, and are then quite insoluble in bisulphide of car- 

 bon. When the altered crystals are melted, and the mass cooled rapidly, it 

 again dissolves completely in bisulphide of carbon. The density of the 

 crystals before being heated was 4'46 or 4 - 509 at 59 deg. F., after being 

 heated it was 4'7. The density of selenium crystallized from a solution of 

 selenide of sodium was from 4 - 7GO to 4*788 at 59 deg. F. 



It appears that the selenium crystallized from selenide of sodium and the 

 granular crystalline selenium arc identical, and essentially different from that 

 crystallized from bisulphate of carbon. In this respect selenium is analo- 

 gous to sulphur, which also exists in two isomeric states, but selenium has a 

 much greater stability in its isomeric states. 



The crystals of iodine obtained in various ways have always the same 

 form, and do not present any of the peculiarities observed in sulphur, 

 selenium, and phosphorus. The crystal form is a rhombic octohedron. 



The crystal form of phosphorus is a regular dodecahedron. 



Very fine crystals of phosphorus may be obtained by exposing phospho- 

 rus to sunlight in a tube either exhausted, or filled with a gas which cannot 

 oxidize it. Professor Mitscherlich states that he has never observed the 

 emission of light from phosphorus during volatilization when oxidizing sub- 

 stances were excluded, so that the emission of light would seem to be essen- 

 tially connected with oxidation. The crystals of sublimed phosphorus soon 

 acquire a red color in sunlight, without alteration of form, but generally it is 

 only the outside that is altered, and the change does not consist in the pro- 

 duction of the isomeric phosphorus described by Schiotter. 



ON THE FOKM OF CARBON, KNOWN AS " GAS CARBON." 



At a recent meeting of the American Academy, Dr. A. A. Hayes pre- 

 sented the following paper, on the form of carbon deposed in retorts used 

 for decomposing coal. 



" This form of carbon has been supposed to result from the decomposition 

 of olefiant gas by heat ; olefiant gas being one of the products of coal de- 

 composition, under certain conditions, olefiant gas is represented by C 4 H 4 , 

 the equivalent being four volumes, and when it is exposed to a temperature 

 above redness it deposits carbon in considerable quantity. If exposure and 

 heat be continued, the final result is carbon, as a precipitate, and hydrogen as 

 a gas, free from carbon. 



" To render probable the supposition of olefiant gas being the source of 

 the gas carbon, it has been generally stated that this bicarburet loses t\vo of 

 its four proportions of carbon by heat, and becomes converted into marsh 

 gas, or light carburet of hydrogen, the formula of which is C-H 4 ; and thus 

 the definiteness of an exact result is presented. 



" In the manufacture of gas for lighting, an increased temperature in the 

 retort diminishes the illuminating power of the gas, and hence it has been 



